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Race Tech's Motorcycle Suspension Bible

• Suspension Tuning, Repair, and Maintenance • Designing Custom Suspension Systems • Modifying and Upgrading Stock Suspension • Tuning Components for Your Riding Style • All Motorcycles: Dirt, Street, and Track

Race Tech's Motorcycle Suspension Bible

Paul Thede and Lee Parks

n__,__.

Dedication T his book is dedicared to those wirh an open mind and a thirst fo r knowledge.

Fo r rhe enrhusiast who wanes co go fas rer or smoorher o r safer o r all of the above.

Firsr published in 20 I 0 by Mororbooks, an imprint of MBI Publishing Company, 400 First Avenue No reh , Suire 300, Minneapo lis, MN 5540 I USA

Copyrighr © 20 I 0 by Paul T hede and Lee Parks

All righrs reserved . Wi rh rhe exceprion of quoring brief passages fo r rhe purposes of review, no pare of ch is publicarion may be reproduced wirhour prior wrirren permission fro m rhe Publisher.

T he informarion in chis book is rrue and complere co rhe besr of o ur knowledge . All recommendarions are

made wirhou r any guaranree o n rhe pare of rhe aurho r o r Publisher, who a lso disclaim any liabili ry incurred in

connecrion wirh rhe use of chis dara o r speci fic derai ls.

"Race Tech," "Gold Valve," "Emulacor," and ocher rrademarked

Race Tech products used by permission of Race Tech.

We recognize, further, that some words, model names,

and designarions menrioned herein are rhe properry of the trademark holder. We use them for idenrificarion purposes o nly. This is nor an official publicario n .

Mororbooks rides are also ava ilable at d iscounrs in bulk

q uanri ry for indusrrial or sales-promotional use. For derails wrire co Special Sales Manager a t M Bl Publishing Co mpany, 400 Firsr Avenue N orrh, Suire 300, Minneapolis, MN

5540 1 USA.

To find our more abour our books, jo in us online ar www.mororbooks.com.

ISBN-1 3: 978-0-7603-3 140-8

Presidenr/CEO: Ke n Fund Publisher: Zack Miller Senio r Ediror: Darwin H olmsrrom

Edicor: Perer Bodensreiner C rea rive Direcro r: Michele Lanci-Alromare

Design M anagers: Brad Springer, Jon Simpson, James Kegley D es igner: Danielle Smith

Prinred in China

About th e authors

Paul Thede is widely considered mororcycling's preeminenr suspensio n guru. H e is rhe owner and chief engineer of Race Tech, rhe largesr mororcycle suspension modifier in rhe world. Paul lives in Corona, Cali fo rn ia.

Lee Parks is rhe besr-selling aurhor of Total Control. Based

on his inrernariona lly renowned Tora! Conrrol Advanced Riding Clinics, Total Control is considered by many co be rhe riding skills bible. Parks lives in Apple Valley, California.

Contents Author's Notes . .. . . ........... . .. . .... •. . . .. .. . .. . .. . .. . . .. . .. .. . . .. . .. . .. . 4

CHAPTER 1

CHAPTER 2

CHAPTER 3

CHAPTER 4

CHAPTER 5

CHAPTER 6

CHAPTER 7

CHAPTER 8

Suspension Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Springs .. .. .... . ..... . ....... . .. .. . . .. ... ..... . ..... . .. 9

Damping . . . ... ... ..... . .... .. .. . .... . .. . ........ . .. . . . 26

Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

Troubleshooting and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Tools and Equipment for Suspension Service ......... . .. . . . 108

Suspension Service Department ... . ................ . .. . . . 113

Appendix 1: Lowering .... . ........ . . ...•. . .. ............. . .. .. .. . ......... 238

Appendix 2: Swingarm Length . .. . .. .. . . . • ... . . .. . .. . .. . .. . .. . .. . .. . .. . . .. .. 239

Appendix 3: Glossary .... . . .. .......... .•.. . ..... .. . .. . .. . .. . . .. . .. . . . . . . . . 240

Appendix 4: Race Tech Motorcycle Suspension Bible Testing Log .. . . .. .. . .. . .. . .. 248

Appendix 5: Race Tech Tool List .. . .. .. . . . • ... . . .. . .. . .. . .. . .. . .. . .. . .. . .. . .. 250

Appendix 6: Resources .. . .. . .. . ........•. . . . . .. . .. . .. . .. . .. . .. . .. . . . . . . . .. 252

Index . ..... . .. . .. .... .. . .. .. . . .. . .. . . •. . . .. . .. .. . .. . .. . .. . . .. . .. .. . . .. .. 253

Authors' Notes

I first swung a leg over a mini bike at the age of 10 and was hooked. My life instantly had direction. I raced

professional motocross, stud ied hard in school because I wan ted to work in the industry, went to college and studied harder, graduating summa cum laude with a bachelor of science degree in mechanical engineering from Cali fo rnia Polytechnic University in Pomona. I started a business with partners buildi ng high-perfo rmance motors and suspension and then opened Race Tech in 1984.

I r d id n't rake long to realize I could drop lap times fa r fas ter by setting up suspensio n than by bu ilding superfast motors. Somewhere in this rimeline I realized I wasn't going to be the next natio nal champ, and while I continued to race, I really enjoyed helping others go fast and stay on the rubber side.

Back in the early 1990s, we tu med ou r attention to road race and street bikes and were blown away with the results. l invented the Gold Valve and the Gold Valve Cartridge Emulator back then and starred to produce products­includ ing a line of suspension tools-chat would help others tune suspension. In 1994 I created the fi rst Technical Edge Suspension Seminar and have taught more than 100 seminars

and rhousands of srudenrs around rhe world.

T hrough the years I've had the privilege of working with many top-level riders like Doug D ubach, Gary Denton, Mike Beier, Jeremy McGrath , Tallon Vohland , Rodney Smith, Ty Davis, Danny "Magoo" Chandler, Jamie James, James Rando lph, Tom Kipp, Lee Parks, Rich O liver, David Anthony, Micky Dymond, Darryl Arkins, Benny Carlson, Josh Brooks, M ike Merzger, Jordan Szoke, Bonneville legend Paul Livingston, M ike and Jeff Alessi, Jake Weimer, Eric and Ben Bostrom, Kerry Peterson and the Peterson gang, Malcolm and Alexander Smith, Brando n T hede (my six-year-old son),

and riders li ke you. In the fo llowing pages, I promise to avoid big words

as rhere is very little value in you being impressed with my vocabulary. In some cases, you may want to read a section more

4

than once, and in face, you may want to read the book many times. I encourage you to use che fo rms available to download free on www.racerech .com. Refer to che Troubleshooting and Testing chapter as you are testing, because ir can "jog the marbles." Use our website to look up suggested spring races and see what's available fo r your model. Feel free to contact Race Tech and ask questions about your specific bike-we have great technical support. Lastly, if you are really in trigued, rake advan tage of our suspension seminars-many of the world's top tuners have done just that.

Ir has been my experience over the years char much of the information availab le o n suspension was hard to understand, incom plete, or contrad ictory. In fac t, much of the most importan t information was sim ply no r out there fo r public consumption. For rhar reason, mosc people fi nd suspension tuning a "mysterious black arc." My goal is to help yo u understand this challenging subject ar a higher level than yo u do now. Be will ing to lea rn someth ing new, and keep in m ind char there is always a "next level" of understanding as well as suspensio n performance. T here's always room for improvement. "The bes t you've ridden is the best yo u know."

Ir is my opinion thar almosr any brand of suspensio n can be made to work well. T his depends mostly on serup. H owever the maximum poten tial can be lim ited by its design. I have immense respect for other suspension manufacturers and tu ners and my hope is that this book complemen ts and enhances rheir work too.

People with many different levels of interest and u nderstanding will read this book. Perhaps you simp ly want a little clarity on a mysterious subject, or maybe you are reading this because yo ur kid races. O n the o ther hand, you might work on suspensio n fo r a living (or you may want to). If you want to become a great suspension ru ner, you will need to be many thi ngs: a detective, a sa lesman, a psychiatrist, a technician, and mosr of all, a student (l ike my son Brandon).

Good luck and great riding. - Paul Thede

Authors' Notes

T o understand the genesis of the Race Techs Motorcycle Suspension Bible is to peer into the minds of three

en thusiasts who love all things that go fas t and smell of ho t o il: Paul T hede, Al Lapp, and myself.

Jn my first book, Total Contro4 it was my mission to demystify the art of advanced riding-as part of that project, l took the bold step of including two chapters on suspension theory and setu p. I did this because so much of proper rid ing technique is about minimizing suspension movement so that the lim ited amoun rofwheel travel remains available to maintain traction . Ir seemed obvious then that part of the advanced riding equation wou ld be to help riders ge t their suspension systems set up properly. And, because I'm a big believer in teaching people how to fish as opposed to simply giving them a fish, we spend an entire hour on suspension in my Total Control Advanced Riding clinics (www.totalcontrolrraining.net).

W hen consulting an expert to help design chis portion of the clinic's curricu lum, there was really only one choice- Paul T hede. Paul has forgotten more about suspension than mos t people will ever know. His abili ty to make that knowledge understandable in a real-world context is surpassed only by his exhaustive understanding of mechanical engineering.

My challenge was co cake a small piece of Paul's depch of knowledge and creace a book that regular motorcyclists would understand .

A true pio neer in motorcycle suspension, Paul shares his knowledge in a most unselfish way. H e teaches many of his most creasured secrets to those who attend his interna tionally acclaimed Race Tech Suspension Seminars (www.racetech.

com). T his means he has trained a huge majority of his future

customers as well as his com petito rs. Ir's virtually impossible to see a modern suspension com pany in business today that has no t been significandy inAuenced by him .

As a form er professional photographer, l knew I'd have no problem with the many how-to photos in the studio, but there was one more critical part chat the book needed­technica l illustrations. For this mammoth task I needed someone with tremendous talen t- enter " Big Al" Lapp. Al is a lo ngtime fr iend , racing buddy, and incredibly talented illustrator. Fo rtunately he is also a big ti me gearhead , equally at home at the con trols of a welder o r lathe as he is with the tablet of his M ac. Al was ab le to make the words and ideas come alive in ways only someone who both understood and loved the material cou ld.

Mark Kalan video taped Paul's six day seminar, which was used as the basis fo r the book. Many people spent cou ndess hours transcribing, whirding down, and editing the information and photos into workab le-sized chunks. l wou ld like to thank Matt Wiley, Tracy M artin , Michael "Pilot" Nelson, Rachel Westfall, Jim Barg, and Lenny Albin fo r their sizeab le contribu tions to the project.

Finally, l hope that when you complete this treatise on

suspension, you will nor so much be impressed wirh whar we know, but be genuinely impressed with what yoi1 know. Too m any authors of technical books have forsaken the average reader in the hopes of impressing their peers. W hi le I hope that we can achieve both, we have gone to great lengths to make chis materia l accessible to the layman as we ll as thought provoking to the engineering elite. If we have fa iled at either one, it was no t fo r a lack of effort.

- Lee Parks

5

Chapter 1 Suspension Basics Why do we need suspension anyway? After all , go karts

go precry darn fasc wichouc any. The simple answer? Bumps. (Well, ho les coo.)

Back in che beginni ng, che wheel was revolutionary, bur wooden wheels and solid axles didn't g ive che mosc com forcab le ride. Springs were added and char was muc h bener, bur che wheels scill kind of bounced around a bic. Pneumatic cires were a huge breakthrough in boch comfort and grip, bu r che wheels scill bounced arou nd roo much. Nexc, che damper was added ro contro l che oscillacio ns, and che modern suspended system was born.

THE GOAL If we were ro describe che ideal suspension, ic would have max imum craccion, minimal harshness (or maximum plushness), contro lled bonoming, consistency (ic would nor fade), control che picch (front-co-back movement) of che bike, have a proper "feel" fo r che road, and so on. Nore char some o f chese characceriscics are concradicrory-like m inimizing

harshness and resisring borroming-and you' ll see rhar we've goc quire a challenge on our hands.

T he basic goals of suspension are rhe same in every vehicle, from a mororcycle ro a car ro a semi rruck. Of course, we wouldn'r sec up a cru iser rhe same as a superbike, and

direction of travel

• •

motorcycle and rider

we wouldn't sec up a crail bike li ke a supercrosser, bur rhe

description of che perfect ride is che same-a bump is a bump and craccion is craccion.

Lee's scare wich che defin itions of sprung and unsprung

mass. Sprung mass is che mass above che spring. This includes che engine, mosc of che frame, che gas rank, sear, rider, and so on. T he unsprung mass is che mass char goes up a nd down wirh che wheel. This includes che wheels, ax les, lower slider on a telescopic fork, brake caliper, pare of che swingarm, and so on.

The rwo essential com ponents in che suspension-the spring and che damper-can cake many forms, bur chey all have che essential job of iso lating che sprung mass from che ground.

In genera l, in che perfect world, che sprung mass should move along in a scra ighc line (or a smooch a rc around a cum) , and che unsprung mass should move up and down, fo llowing che ground. Ideally, when going over bumps, che load berween che tire and che grou nd should remain

co nstant, with the same load on the up side as the down side. (One of che few exceptions to this is in supercross "whoop" sections where the fastest way across is ro get "on rop" of che bumps and never lee che wheel drop inro the low points between bumps.)

uncontrolled oscillation causing loss of traction

severe loss of traction on back of bump

1.1 Without suspension the wheel is solidly attached to the chassis. When the wheel hits a bump, the chassis is displaced violently (it's harsh). It continues upward past the crest of the bump. The wheel loses contact with the ground. When it comes back down, it bounces.

6

T he techno logy required to create the perfect ride is still

no t here (this is particularly true fo r mo to rcycles), bu t this is

the goa l.

Now fo r the millio n-do llar q uestio n: how do we accomplish this? To begin , le t's look at the forces involved

with suspensio n. Certa inly there are ine rtial fo rces-bo th linear and rotatio nal- but lee's focus o n t he three main fo rces

in suspe nsio n com ponents: sp ri ng fo rces, damping fo rces, and frictio nal fo rces . Thar's it. T ha t's all there is. Suspensio n

is sim ple! Now befo re you skip to the end of the book to see how it rums out, le t's take a close r loo k.

direction of travel • )Ii

sprung mass

unsprung mass

spring only

SPRING FORCE T he two basic types o f springs a re mechanical and air.

M echa nical springs come in t hree different fo rms: co il, leaf,

and to rsio n bar, with co il springs being che most commo n

o n motorcycles. The fo rce o f a co il spring depends o n wi re

d iameter, coil d iameter, number o f coils, and materia ls .

Air springs, o n che ocher hand, have p ro perties like

initial pressure, compressio n ratio, and effecti ve p iston

area. The main thing to know about spring force is that it is dependent on position, meaning the distance the spring is compressed.

less upward acceleration, smoother ride

uncontrolled osci llation of sprung mass can pull wheel off ground, causing loss of traction

1.2 When a spring is added, notice that the chassis initially moves upward but not as much as without suspension. It is not as harsh. Once it moves initially, it oscillates uncontrollably. The wheel still loses contact with the ground but not as much. When it comes back down, it doesn't bounce quite so much.

direction of travel • )Ii

sprung mass

unsprung mass

spring and

damper

smoothest ride

minimal loss of traction

no uncontrolled motion

1.3 When a damper is added, notice that all the unpleasant characteristics are minimized but they're not gone. The sprung mass only moves upward slightly. The wheel still loses contact with the ground but for a much shorter time. When it comes back in contact with the ground, it remains in contact.

7

en c: en ~ m z en C5 z m ~ 0 en

en (,)

~ CICI z 0

~ w Cl.. en :::> en

DAMPING FORCE Damping forces depend on o il viscosiry, o rifice sizes , piston size, valving, shim co nfigurarion, and mosr of all , velocity.

I r is worthwhile to nore rhar we are referring to damper

ve lociry-how fasr rhe damper compresses or rebounds-nor vehicle veloci ry.

FRICTION FORCE Fricrional forces depend o n rhe marerials in conracr (rhe coefficienr of fricrion) , rhe normal fo rce (rhe force perpendicular to rhe surfaces in conracr) , and wherher rhere is movemenr o r nor (if rhe forces are sraric or dynamic).

ENERGY On rhe energy level, springs score energy. In ocher words rhey rurn kineric energy (energy due ro morio n) inro porenrial o r

direction of travel

• • unsprung

mass

spring and

damper

stored energy. D ampers and fr icrion borh rurn kineric energy inro heat. W hy in the heck are we looking ar energy? Ar a basic level suspension setup is force and energy management.

A su btle no re at chis poin t, if rhe shock gees hoc during use, it's do ing its job. More damping means m ore hea r. The mo re and rhe bigger rhe bumps a re and rhe faster you hit rhem , rhe mo re energy is converred inro hear. T he m ore hear, rhe horrer rhe shock gers. Many ride rs have misrakenly rhoughr rhar if rhe shock gers ho t , something is wrong.

In rhe fo llowing pages we will rake some of rhe mystery our of rhe black arr of suspension. Keep in mind char "suspension is simple." Thar may seem like a joke, bur once yo u ger a clear grasp of rhe fundamenrals, ir will be much easier ro comprehend the more complex aspecrs. Lee's srarr wi rh springs.

sprung mass moves in a straight line

maintains perfect traction

J 1.4 In the perfect world, the center of gravity of the sprung mass doesn't move vertically. The wheel remains in contact w~h the ground at all times. This can only be achieved with active suspension where the wheel is sucked up on the face of the bump and pushed down on the back side. The technology to do this is not here yet, but this is the ideal ultimate goal.

8

Chapter 2 Springs While everyone knows basically whac a spring is, few

understand how spring forces affect suspension accion. In che fo llowing pages, we' ll cake a closer look ac spring fo rces

a nd che d ifferenc cypes of springs used on mocorcycles.

SPRING FORCE Springforce is che flrsc of che chree forces in suspension we will

look ac. When seccing up your suspension, geccing che co rrecc

spring race and preload is crucial, so ic should be done before

a ny ocher changes are made.

T he mosc importanc ching co know abouc springs is

chac che spring fo rce is dependent o n how much che spring

is compressed-chis is referred co as spring displacement. For

example, if it cakes I 0 kilograms(kg) o f force co compress a

spring l millimecer(mm) , che spring's race would be I Okg

per mm. So if you wane co compress chis parcicular spring

Smm, how much fo rce would ic cake~ The answer is 50kg.

Ten millimecers of spring compression would cake IOOkg

o f force, and so on. T hus, che amounc of force the sp ring

pushes back is dependent on how far it's being compressed.

[e's importanc co remem ber chac springs are displacemenc (o r

posi cion) sensicive.

T he coca! spring force creaced in telescopic front fo rks

is a bic more involved. T his is because chere is a volume of

air trapped inside che fork cubes chac acts like an addi cional

I ~ ~ ~ free

length ~

l ~ .;::=::

K (spring rate)

spring compressed

20 mm

10 kg 20 mm

spring. W hen front forks are compressed, the air pressu re inside che fork increases, even if no inicial air pressure was

used in che fo rk. T he more the fork compresses, che more

progressive che "air spring" becomes. Basically, the front forks

have cwo spring forces: 1) the mechanical spring force, and 2) che air spring.

SPRING RATE Spring rate is che "sciffness" of che spring, co mmo nly measu red

in kilograms per millimecer (k/m), pounds per inch, o r

newcons per millimecer. One way co resc spring rate is co flrsc

measure rhe spring's "free lengch" (the un installed length),

t hen puc a known amount of weight o n che spring , and

measure che amount ic compresses. Spring race is calcu laced

by dividing che fo rce by che displacemenc. Noce: Spring race is

more commonly measured by compressing ic in displacement

increments and measuring che add itiona l load.

By placing increasingly heavier weighcs on che spring

and measuring how much ic compresses, a graph of force

versus displacement can be plorced. If we place a I Okg

weighc on the spring and ic displaces 20mm, che spring race

is calcu laced as fo llows: 10kg/20mm = .Skg/mm. A I kg/mm

spring would displace lOmm wich che same l Okg weighc

added : lOkg/IOmm = I kg/ mm. More on chis in che seccio n

on measuring spring races.

.5 kg/mm

2.1 One way spring rate can be calculated is by applying a known amount of force and then dividing that amount by the distance the spring travels.

9

100

90

80

70 en

..:.:: - 60 LL

G,) y

50 ... Cl

LL en 40 c: ... c.

(I) 30

20

10

/ /

/ / r spring rate: 1 the slope of the

l 1.0kg/mm ~ I/ line represents the spring rate

y -------~

v ~ ..----

v ..---- ~

------ ~ spring rate: 1 v ------....-...- 0.5 kg/mm j

P-~ 0 0 10 20 30 40 50 60 70 80 90 100

Spring Travel (D) mm. 2.2 This is a force-deflection curve for two different-stiffness springs. The blue spring requires 5kg additional force for each 10mm increment through its entire range. The red

~ spring is twice as stiff, so it has twice the slope, requiring an additional 10kg for each 10mm increment. z a: Cl.. en

T here are three basic types of spring designs: straigh t-rate,

dual-rare, and true progressive. A straight- rate sp ring maintains

a co nstant rate th roughout its travel and is very co mmon in

racing applications. The co ils on a straight- rate spring are spaced

evenly. Each additio nal displacemen t increment (m illimeter o r

inch) takes the same amount o f additional force to compress it

as it goes th rough its en tire travel.

Progressive springs , by co ntrast, change thei r rate in

relatio n to where they are in the travel. Progressive sp rings

come in two main va rieties: dual- rate and true progressive.

A dual- rate spring co mmo nly has two differen t co il spacings

alo ng its length- one is closer together, whi le the other end

has the coils spaced further apart. As the spring co mpresses,

a ll the co ils co m press at the same rime. The closer-spaced

co ils run ou t o f travel soo ner (the co ils touch each other and

therefore have no travel remaining). They are then " blocked

o ur," making the spring stiffer. Stacking two different sp rings

o n top o f each o ther can also create a d ual-rate spring.

A true progressive spring has coils that start out close

together, and then are spaced progressively further apart with

each successive coil. Initially, the sp ring fo rce changes o nly a

small amo unt with each incremental change in displacement.

As the spring compresses, the coils are progressively blocked out,

making its rate change gradually. A progressive rate can also be

accomplished by using tapered wire, but a t a much higher cost.

10

[teiiii"ersP!§J

crossover spacer

coil alignment spacer

( main spring J

A B c 2.3 One method of creating a dual-rate spring is to stack two springs on top of each other. We can control the crossover point with different length spacers that block out the secondary or "tender" spring.

100

90

80

70 en

..:.:: - 60 LL

G,) y

I I

J v l straight-rate l / spring

/} / ~ r dual-rate 1 ~~ 50 ... Cl

LL en 40

l spring

~~ ~ ~ ~

c: ... c.

(I) ~ A 30

20 ~ v "' ~ J pro~ressive 1

l spnng 1

10 ~ ~ ~ -- ~

~ ~ ~ 0

0 10 20 30 40 50 60 70 80 90 100 Spring Travel (D) mm.

2.4 Progressive springs gradually increase force through their travel, while dual-rate springs have a distinct "crossover point" where they change rates. Straight-rate springs have a constant spring rate.

From left to right: straight-rate, single spring dual-rate, stacked dual-rate, and true progressive rate springs.

W hich sp ring type is berrer is a marrer of app licarion

as well as opinio n, bur Race Tech recommends srraighr- rare

springs in mosr relescopic forks. Here's wh y. W hen serring

up rhe spring rares on suspensio n, rhe ideal serup is o ne rhar

is progressive eno ugh yer nor roo progressive. A spring rare

rhar is nor p rogressive eno ugh will rend ro be a compromise.

I r may have a rendency ro feel roo harsh o n sma ll bumps

and addirionally may bo trom out when hirring a large bump.

A spring rare rhat is roo progressive wi ll cause rhe suspension

ro drop rhrough irs rravel roo easily during rhe first parr of

movemenr, causing a mushy feeling. Addirio nally, as rhe

suspension conrinues ro compress, ir may become roo stiff

roo fast and feel harsh.

Remember char in relescopic forks there are two main

spring forces: the mechanical coil spring and the air spring.

By irs very nature the air sp ring is very prog ressive and can

easily be tuned wirh o il level. Race Tech has fo und rhar

rhe combinarion o f a srraigh r-rare spring and rhe narurally

occurring, progressive air spring offers the besr combinarion

of fro nr suspension p rogressiveness. In facr, if more

progressiveness is desired, a simple increase in fork o il level

may be all char is necessary.

On rhe rear o f d irr bikes and ATVs w irh no linkage,

resring has shown char progress ively wound springs o r even

dual- and rriple- rare springs perform the besr. This can

m ake rhe wheel force curve similar ro rhar o f a linkage

setup. Srreec a nd road race rear suspensio n does nor require

much, if a ny, rise in rare and work fi ne wirh srraighr­

rare sp ri ngs.

Straight-wo und springs a re also easier ro understand in

terms of their spring rare. Conversely, the only way co acrually

see how rhe fo rce of a progressive sp ring cha nges is by using a

spring cescer co map o ur the spring forces.

11

en Cl z a: Q... en

For example, if a simple dual-race spring is marked as

a 0 .5 to 1.0 kg/mm spring, its ini tia l race is 0 .5kg/m m . Bu e

chere's a problem : where does che 1.0 kg/ m m race scare?

W ichou c consulcing che manufac turer o r tescing it yourself,

yo u wouldn'c know.

Many peop le mis takenly ask whac che in itial and final

races are. T his information is very misleading. To illustrace

chis pro blem look ac Figure 2.5. We have plo cced ch ree dua l­

race springs. All o f them scare wich che same inicial race o f

.5kg/mm and all o f chem end wich a race o f 1.0 kg/mm.

T hey are, however, dramatically differenc, simply by vireue

o f having differenc crossover po incs. (The crossover po inc is

the po int in the travel where the rare changes.) Notice thac

wirho uc chis in fo rmation , the initial and final rates are almost

worthless in describing the spring. W here the rare change

occurs causes a huge difference in how the suspension reacts,

so it's noc so simple.

A st raight- rare spring is much easier to underscand (a

0 .5kg/mm spring will always rake an additional 0.5kg o f

force co move it each additio nal millimeter) , so you end up

with suspension chac is easier co ru ne.

Keep in mind char we wane eno ugh p rogressio n bur na e

coo much. On the rear of mo corcycles, there are linkages with

very lirrle rise in rare as they are compressed. Some franc

A-arms o n ATVs have che same problem. In chese cases a

-LL

Cl) (.) ... Q

LL en c::

·.:::: c. en

progress ive o r d ual-rare spring-or even a triple-rare spring­

can be appropriate.

How do you know what spring rare is correct fo r your

motorcycle? Use che mechods ou tlined in che " how ro measure

sag" section lacer in chis chapcer to determine if the existing

spring race is coo hig h o r coo low, and then cake a n educaced

guess as co whac your ideal spring race sho uld be.

An easier way is to go ro www.racecech.com and use

che o nline spring race calcu laror-jusc look up che make,

model, and year o f che motorcycle you wa n t for a spring race

ca lculacio n . Selecc che cype of riding and enter the rider's

weighc wichouc any gear. T he recommended spring race

shown on che calculacor sho uld be wichin a few perce nc of

che ideal sp ring race, cho ugh ic may na e be exact. Jusc selecc

che available race rhac is closesc co the recom mended rare. The

scock race is shown as well fo r comparison.

STACKING SPRINGS A number o f design paramecers affect spring race. One o f these

is che number o f coils. By increasing che number o f spring coils,

the spring race becomes sofcer. This is contrary co what many

riders ch ink abouc springs-chey think chac more coils (sp ring

material) sho uld equal a s tiffer spring race, bu r che opposite is

crue. Imagine rhac you have a sp ring wich a rare of l Okg/mm

and you puc l Okg o f fo rce on ic-ir would compress lmm.

10 20 30 40 50 60 70 80 90 100

Spring Travel (D) mm. 2.5 Shown are three dual-rate springs all having the same initial (0.Skg/mm) and final (1.0kg/mm) spring rates but having different crossover points. This illustrates the challenge of naming these springs. Note: This could also be created with stacked springs instead of being built into individual springs.

12

Imagine taking ano ther identical !Okg/ mm spring and

stacking it o n top of the fi rst. If we put I Okg o n the first

spring, bo th springs will compress Imm for a total of 2mm.

T hus, the combined spring rate wo uld be 5kg/mm (K =force/

displacement o r ! Okg/2mm = 5kg/mm). T he combinatio n

o f both springs lowers the o verall spring rate. T his is called

springs in series.

T he fo rmula chat governs this is:

I I 1 I -=-+-+-+ K, K, K2 K ...

K, - To tal Spring Rate K

1 - Spring Race of First Spring

K2

- Spring Ra ce of Second Spring

K .. . - Ere. Spring Race

In o ur example of rhe two stacked ! Okg/mm springs, the

formula would look li ke this:

I/ K = I / I O+ I / I O= 0.1+ 0.1 = 0 .2

K = 110 .2 = 5kg/mm

Perhaps it's easier to visualize a torsio n bar spring like

the one used in the VW Beede rea r suspensio n. T he spring is

noc a coil buc a scraighc, round sceel bar. Imagine che torsion

Q) (.) ... Cl LL Cl

= ... Cl. en

combined spring l force is coil spring ' plus air spring

... ~

~ ~

....-

d~ ~

bar was clamped in a vise and the other end had a hex nut

welded to it. You could put a torque wrench o n the end and

app ly a specific torque and then determine the spring rate by

recording the amount of rotation. Now if rhe bar were rhe

same diameter bur twice as lo ng, it would rotate twice as far

with the same amount o f to rque applied.

The length o f the torsio n bar relates to the number of

co ils in a spring-the fewer the coils (or the sho rter rhe piece

of bar stock), the stiffer the rate . T he greater number o f coils

(o r the lo nger the bar stock), the softer it is. Again, when

two springs are stacked, the number of total coils is increased ,

causing the spring rare to be reduced.

Conversely, rem oving co ils makes the rate stiffer. Race

Tech has a triple- rate fork spring kit tha t illustrates the

concept. T he kit is no t m ade to be progressive, as it wou ld

firs t seem. Rather, it is made to provide m o re tha n o ne

rate. It comes w ith o ne main sp ring-a regu lar, fu II- length ,

m ain fork sp ring, a nd two s ho rt, secondary sp ri ngs that can

be stacked o n top o f the m ai n sp r ing. This allows the user

to choose different combinatio ns o f sp rings a nd change

the spring rate. Using the m a in spring by itself provides

t he stiffes t spring rate (0.46kg/mm in this exam p le). If

o ne of the sm aller springs is added to the main spring,

t he new sp ring rate is 0.43 kg/mm. I f all three springs are

stacked up , the resu lting rate is about 0 .40kg/mm. With

the additio n o f each spring, the combined rate becomes

sofcer. By removing springs, che race gees sti ffer.

/ /

/ r combined 1 I spring force~ v

~

v ~ ...........-

/

/' v ~ k ~

~ l coilspri~

air spring ~ ~

>------L---~"' ' l---~

Fork Travel 2.6 The total spring force is a combination of mechanical spring and air spring.

13

en Cl z a: Q., en

Ir's in teresting and important to note rhar two springs placed in parallel (as used on front fo rks) add ro each o ther, stiffening rhe overall o r com bined spring rare. If you are running rwo .46kg/mm springs in you r dirt bike fro nt end, rhe combined rare is .92 kg/mm . T his technique is commonly used to "split" rares. A .95kg/m m spring in o ne leg and a 1.0 kg/mm spring in rhe other gives a to tal of 1.95 overall. T his is equal ro two .975 springs.

AIR AS A SPRING AND OIL LEVELS All telescopic motorcycle forks contain an air space-as rhe fo rk is compressed , rhe air space gets smaller and its pressure increases. W hen o il is added in rhe fork rube, rhe air space is reduced , and rhe compression ratio is increased. T he air spring inside rhe fork rube works in parallel with rhe mechanical springs, and therefore rhe fo rk oil level has a direct relationship to rhe overall stiffness.

On motorcycles with air valves built into rhe fork caps, iris nor generally recommended to use air as anything more than an emergency tuni ng variable. T his is because adding air can increase harshness no ticeably (due to additional seal drag or excessive topping out) and , unless the added pressure is excessive, only yields a relatively small beneflr in bottoming resistance. Adding air is almost like adding spring preload (nor spring rare). On touring bikes, however, rhe use of additional air pressure is quite effective for temporarily changing the load-carrying capacity

for riding rwo-up. The air valve also is handy for bleeding off excess air pressure that can build up because of temperature and altitude changes as well as air leakage past the seals.

Changes in oil level affect the total spring fo rce. Due to the progressive narure of the air spring, rhe change in spring force will be noticed more in the last part of rhe stroke as rhe fork reaches rhe borrom .

SPRING DESIGN AND MANUFACTURE Coil-type springs are used in most motorcycle suspension. However, springs can rake on many forms, including torsion springs (round bar stock rwisred axially), leaf springs (flat o r curved metal bars, mostly used on o lder cars and trucks),

Belleville diaphragm springs (conical washer-shaped springs char are used o n some motorcycle and automobile clutches),

and finally air or ni trogen bladders o r chambers. Springs can be made of a variety of materials, including

steel, titanium, or even carbon fiber. Heat-treated steel

14

springs are by far the most common o n motorcycle and ocher powersport vehicles.

H igh-performance springs are rhe most desirable and rhe most difficu lt to produce. O ur defin ition of a high­performance spring is one rhar is physically light for its given rare. T he fo llowing is the formula char manufac rurers use to design coi l springs using rou nd cross-section wire:

d4 x G K= ----

8 D3 x N

K - Spring Rate d - Wire Diameter G - Modules of Rigidi ty, a material property

(G for chrome silicon spring steel-8, 102kg/ mm 2

o r 11.5 x 106 lbs/in 2)

N - Number of Acti ve Coils (Squared and Ground subtract 2 Coils) D - Mean Coil Diameter (mid coi l)

This can look a bir com plicated, bur if we take a moment, ir can explain a !or. Notice char wire diameter is in rhe numerator (top of the fraction). T his means as we increase wire diameter, rhe rare gees stiffer. Notice also rhar N (nu mber of active coi ls) is in rhe denominato r (bottom half of rhe fraction). T his means that rhe more active coils a

spring has, the softer it is (we d iscussed this when we talked

about stacking springs in series). This means springs can be designed very differently and end up wirh the same rare. Two designs, one wirh heavy gauge wi re and lots of coils o r a second design wirh chi n wire and few coils, could be rhe

same stiffness. How is this important in rhe real world~ First, think

abou t how much rhe spring ac tually weighs. The sp ring wirh the heavy gauge wire and lots of coils wou ld be considerably heavier than rhe light gauge wire wirh fewer coils-thus; rhe

fi rst design would nor be preferred. Secondly, rhe spring wirh the ligh t gauge wire wirh fewer coils wi ll have more travel.

The downside to small wire diameter is char much higher quality (and more expensive) material must be used. Also,

because o il level is genera lly measured wirh the spring out, this difference in volume affec ts rhe air compression ratio in the fork (a spring chat weighs more rakes up more volume = higher com pression ratio= higher effective oi l level).

The top spring here has heavy-gauge wire and a lot of coils and is a low-performance spring. The lower spring is a high-performance spring that has small-gauge wire and fewer coi ls. It may be surprising, but these two springs have identical spring rates.

35

6F ( 6F2 - 6F1)

30 - K.,v = - = 60 ( 602- 601)

po int 2

25 = .:.:: -u.

20 G,) c.:I ... Q u.

= 15

(change in force) 40mm, 20kg - spring rate = 02, F2 (change in displacement)

~ / / J(l.

/ c: -... Q,

(I)

10

/ point 1

/ 6F=F2- F1

10mm, 5kg ~

01, F1

5 n / / 1'7

/ ~ [ 1

~

/ ..... 60=02- 01 ,?

0 0 10 20 30 40 50

Spring Travel (D) mm. 2. 7 Calculate Spring Rate ·Average spring rate is the slope of the force-deflection curve.

Here is a rather o bscure rea l-wo rld example of why using

a h ig h-performance sp ring can really m ake a d ifference. O ld

35mm Ha rley-Davidson fo rks are pretty small in d iameter fo r

a 600-po und motorcycle, so the fork tubes have really thick

walls to help suppo rt all that weight. W ith a small tube and

very thick walls, there is little room inside to accommodate

the spring an d mainta in the correct oil level.

Some aftermarket springs that a re ma nufac tured fo r

these fo rks use thick wire: they are low-performance, bu t less

expensive to make. T he p roblem is that these springs rake up

too much volume, so much rhar there isn't eno ug h vo lume

left inside the fo rk fo r the o il to cover rhe dam ping rod. If

you use che recommended o il level and the suspension is

com pressed , the air space is used up and the fo rk " hydrau lic

locks." T his means char rhe suspension bottoms o n the o il

even tho ugh there should be suspensio n travel left.

T h is brings us to a very fine poin t. A sp ri ng rakes

up a certai n volume within the fork depe nding on its

d imensions-if che spring is changed, and the new spring

d isplaces a different vo lume, the o il level wi ll have to be

adj usted accord ingly.

To calcu late the volume che spring d isplaces, you cou ld

weig h it and divide by its density. For exam ple, if a steel spring

weig hs 292 g rams and the density o f steel is 7 .87 grams per

cc then , you would di vide 292 gram s by 7.87 grams, to gee

37. lee. In 4 1 mm forks, lOcc is equal to approximately I Omm

of oil level. I f you were to swap in springs rhar displace mo re­

going from 37cc to say 67cc-rhis equals a 30cc change. The

result is like changing your o il level 30mm . T har's a lo t.

Ano ther thing char is critical to sp ring perfo rmance is rare

tolerance. "Industry standard" spring rare to lerance is plus o r

minus 5 percent (+/- 5 percent) . T h is m eans if a shock spring

is rared at 5 .0 kg/mm, the spring could actually have a spring

rare between 4 .75 and 5 .25kg/mm. A sp ring marked 5.2 could

be 4.94 to 5.46. As you can see, the rates can overlap. T he only

accurate way to confirm the actual spring ra re is with the use

o f a ca lib rated spring rester. Race Tech springs are stringen tly

rested, so our tolerances are much , much righter. T his provides

significantly mo re consistency and easier suspension nming

bur also obvio usly costs us a bi t mo re.

Sometimes springs will get sho r ter with use-this is

known as spring sacking. T his used to be q u i ce a p rob lem, and

consequently service manuals commo nly have a m inimum

spring lengrh tolerance fo r refe rence. Ir is impor tant to no te

rhac sacked-out springs have nor lost their race, o nly their

length. (This is no r true fo r engine valve springs: they sack

because of exposure to high temperatu res.)

If the length decreases, the preload decreases and the

suspensio n fee ls softer. Race Tech springs are p re-set (sacked

o ur) at the facto ry, so they won't change lengths when in use.

The p rocess of pre-setting a spring involves compressing the

spring co coil bind (this occurs when all the sp ring's coi ls

15

en Cl z a: Q., en

touch each other) a few times until the spring "sets" to its fina l length. Once a sp ring takes a set, it is done sacking. T his virtually elimina tes the problem.

MEASURING SPRING RATE T he fo llowing table and graph will help you understand how to measure spring rate. If we test a spring on a spring tester we measure travel (displacement) and force. Unlike the first example, we measure the fo rce at incremen tal known displacements. (Previously, we put on a fixed weight and measured how much it compressed .) Average spring rate between two points (K) is defined as the change in fo rce divided by the change in displacement.

Calculating Average Spring Rare between Two Points from Test Dara

Kav = ~ = (F2 - F l ) g t.D (02 - 01)

(change in fo rce from point 1 ro point 2)

(change in displacement from point 1 to point 2)

We have arbitrarily decided to use 1 Omm increments fo r displacement. The first point is zero displacement. Ar rhis point che load cell would show che weighc of che spring. We subtract chis weight off of all measurements by "zeroing" rhe load ac chis po int.

If you are serious about working with suspension for a living, lntercomp makes this compact digital spring tester. A fork spring tester kit can be added on to this base unit as well.

16

Next we crank che spring down 1 Omm and read che force. In chis example ic reads 5kg. If we compress ic to 20mm, ir reads lOkg. If we compress ic to 30mm, ic reads 15kg, and so on. T his fo rce data goes in che "force" column.

O nce we have displacement and force data, we can plot the daca on che graph and calculate che spring race. In che table to che right, we've done rhe mach. The t.D column is the incremental change in displacement. T he G reek symbol delta (t.) is quire often used to designate "change." We also ca lculated rhe incremental change in force in the t.F column.

Spring rate K is equal to che change in the fo rce d ivided by the change in che displacement. As you can see, che race in this example is 0.5kg/mm. Ir is imporcanc to note char we are actually calculating che slope of rhe line. Notice chis is a srraighc-rate spring as rhe Une is straight. In rhis "perfecc­world" example, we could have used any two points and gocren the same 0.5kg/mm result.

Wich a straight-rare sp ring, the fo rce increases as you compress ic, but rhe rare doesn't change.

We plorred rwo springs on Figure 2.2. W ich che blue ploc, when we crank this spring down 1 Omm, we'll have 1 Okg of force. If we crank rhe spring down 40mm, we have 40kg. Putting chis data into rhe fo rmula, we calculate rhar rhe spring has a rare of l .Okg/ mm. As previously mentio ned, rhe spring rate is rhe slope of rhe line-if rhe spring has a steeper slope, it is a stiffer spring. In the case of rhe spring on rhe graph, ir is rwice as stiff (and thus

the line is twice as steep) as the softer spring shown .

SPRING PRELOAD Spring preload is one o f che most misunderstood concepts when discussing suspension. Often we hear riders talk abou t adjusting their mo torcycle's spring preload to make rhe spring stiffer or softer. T his is a misconception: changing spring preload does nor change rhe spring rare ac all. T he spring has rhe same rare regardless of how rhe preload adj ustment is ser.

Let's look at what really happens. W hen a spring is installed in either rhe front or rhe rear suspension, the spring is typ ically compressed a small amount. T he length rhe sp ring is compressed is referred ro as preload. Specifically ir is defined as rhe distance rhe spring is compressed from ics free (or uninsralled) length to its installed length wirh the suspensio n fully extended, Most vehicles, including motorcycles,

use positive spring preload (negative preload means rhe suspensio n compresses before hitting rhe spring). T his is true even for bikes rhar don't have external preload adjusters. Even

suspensio n wirh rhe external preload adjusters backed our all rhe way commonly still have some preload.

Let's now introduce rhe concept of preload fo rce (which is different rhan preload length) . Preload force is rhe in itial fo rce rhe spring exerts o n rhe end of rhe fork rube- or rhe spring co llars of a rear shock-with rhe suspension fully extended. This fo rce is easy to calculate:

Fo rce= Spring Rare x Displacement

Point Displacement (mm) Force (kg) Change in D (tiD) Change in F (tif) tiF/tiD Spring Rate

0.0 0

2 10.0 5 10--0=10 5--0=5 5/10 0.5kg/mm

3 20.0 10 20-10=10 10-5=5 5/10 0.5kg/mm

4 30.0 15 30-20=10 15-10=5 5/10 0.5kg/mm

5 40.0 20 40-30=10 20-15=5 5/10 0.5kg/mm

6 50.0 25 50-40=10 25-20=5 5/10 0.5kg/mm

7 60.0 30 60-50=10 30-25=5 5/10 0.5kg/mm

8 70.0 35 70-60=10 35-30=5 5/10 0.5kg/mm

2.8 Theoretical "perfect world" spring test data.

100

90

80

70 en

.:.:: - 60 u.. Q)

___....,.. ~

7~v

c,)

50 ... = LL en 40 c ·a:: =-(I)

5~v 30

20

3~~ 1~ ~

10

0 0 10 20 30 40 50 60 70 80 90 100

Spring Travel (D) mm. 2.9 This graph shows the theoretical raw data points and a line "connecting the dots."

W ith a given amount o f preload fo rce on the spring, it will

rake that same fo rce to ini tiate suspension movement w hen the

suspensio n is fu lly ex tend ed. As preload is increased, it takes

more fo rce to cause the fork o r shock to begin to compress.

W hen preload fo rce is decreased , less force is required to

cause movemen t. Ir is important to no te that when the

motorcycle is resting o n the ground with the rider on board,

the suspension is com pressed . W hen preload is changed the

sprung mass is held higher o r lo wer. T h is means more preload

d oes not requi re mo re fo rce to initia te movement o nce the

weight o f the bike has com pressed the suspension.

A consequence of too much spring p reload that results

in the suspensio n being too ex tended is that there will not

be eno ugh travel available for the suspension to ex tend into

holes. T h is can cause tires to lose tractio n as they skip over

d epressio ns in the road 's surface. O n the other hand, too li ttle

p reload squanders ground clearance in corners and can cause

the suspensio n to bo tto m o ut mo re easily.

17

en Cl z cc Cl.. en

pre load

~ •

2.10 Pre load is the amount the spring is compressed when installed with the suspension fully extended. It is the difference between the free length and set length of the spring.

l ~ t I ~ free ~ c=:? length installed

~

l length ~

~ i I~ .;:::::: installed length is ~ I m'"""' w;th ~ the shock fully @ extended

G raph 2. 12 (page 20) shows the difference between

addi ng preload co a sofre r spring (b lue line) compared to a

stiffer race spring (red line). Notice chat the two lines cross

at the 30mm fo rk trave l mark. T his means char bo th o f these

setu ps provide the same amount of fo rce to hold the bike up

at 30mm in the travel. The stiffer spring builds force ata faster

rate (it is stiffe r) but star ts off at a lower initial fo rce. It will

actually "feel" mo re progressive than the sofrer spring with

more p reload. Reme mber, however, chat mo re p rogressive is

no t necessarily be tter.

SUSPENSION SAG T he ma in thing spring preload ad justments rea lly do is

change the ride height. A change in ride he ight affects what

perce ntage o f suspensio n travel is avai lab le fo r abso rbing

bumps a nd fo r ex tending in to ho les o r d ips in the road surface. To understand how chis affec ts the suspensio n's

abi li ty to handle bumps and d ips in the road , you must first

understand suspensio n sag (o r race/static sag). Note a lso chat

it affects chassis geometry and handling. See the geome try

chapter fo r mo re details.

T he concept of sag is simple. W hen a rider sits o n a mo to rcycle, the suspensio n moves downward , o r "sags" under

the rider's weig ht. Sag is the amount that the motorcycle's

suspensio n compresses from fu lly ex tended with the rider o n

board. How much the bike sags depends on che spring rate,

the sprung weight of the bike and rider, and the preload.

Refe rring to Fig ure 2 .13, the line at the bo tto m

rep resents a level road surface. Above the surface o f the road

are potential bu mps chat will be absorbed by the suspensio n

du ring compressio n. Below the road su rface are po tential

18

dips, o r depressions, which the suspension will ex tend into

as the motorcycle moves fo rward. T he illust ration shows the

effect of a three-seep preload adjuster.

Imagine char with o nly the weight o f rhe bike acting o n

the suspensio n (far lefr o f figure) it is nearly "copped o ut,"

meaning 95 percent of the suspension's travel is available fo r

absorb ing bumps. N o tice chat the three-seep ramped p reload

adjus ter is set to its middle setting.

When the weight o f the rider is added (second fro m left) ,

t he suspension sinks dow nwa rd, o r sags. Now 7 5 percent of

suspension travel can absorb bumps, and 25 percen t is left to

ex te nd into ho les. In the next drawing, the preload adj uster

has been set to its lowes t, o r sofrest , setting. This moves the

po int o f com pression and extensio n downward so cha t 65

percent o f the travel is now ava ilable for compressio n and

35 percen t for ex tens ion . (le is impo rtant to no te chat the

total a moun t of suspensio n travel always rema ins the same

a t 100 percent.)

In the last o f the series o f drawings, the p reload adjuster

has been moved to its highest, o r stiffest, setting. The po int

o f compression and ex tensio n has been moved up, a nd now

85 percent o f the travel is available to absorb bumps and 15

percent can exte nd into ho les.

The correct sag fo r motorcycle suspensio n can depend

o n a number o f things-including chassis geo metry and type

o f use-but in genera l it should be somewhere around YJ of the suspensio n's total wheel travel. T his number changes with

application (see tab le o n page 2 1) but it is im po rtant co keep in

m ind chat all these numbers are derived ch rough testing. W hen

we test eno ug h bikes, we find trends. The trends help shorten

t he testing process, but do n't fa ll in love with a particular

number. Every si tuation has un ique elements, and the correct

number depends on the specific applicatio n a nd rider.

Note that a particular sag number can be ach ieved w ith

dramatically d ifferent spring ra tes. Perhaps a spring rate that

is too soft using lots o f preload, o r a really stiff spring using

very little preload . With either of these scenarios, the quality

o f the ride w ill suffer. T he spring w ith a rate that's too soft

will d ive and bo tto m easily. The spring with a very stiff rate

will feel harsh , as it bui ld s fo rce too fas t and will no t move

eno ug h when hitting bumps.

By raking a few sag measurements, the ballpark spring

rate can be determined: we' ll discuss that in more derail later

o n in this chapter. In general, at the rime of this writi ng,

most s treet bikes are se t up with fork sp rings that are too

soft for aggressive riding even o n the street tho ugh there are

exceptio ns. Racers generally use higher sp ring rates w ith less

preload than street riders.

Personal preference, riding conditio ns, and type o f riding

are a ll impo rtant factors to co nsider when setting up sp ring

rates and suspensio n sag. T he stock suspensio ns of mod ern

M X b ikes are all over the place rate-wise as to the ideal rid er

weight. Trail bikes are generally und ersprung. Don't make the

mistake of crying to set up your street bike like a racer, or

yo ur endu re bike like a su percrosser. When in d o ubt, co nsult

www.racerech .com or a good suspensio n tuner.

100

90

80

70 Cl

.::.:: - 60 LL

Cl) u 50 ... 0

So far we've o nly d iscussed static sag. D ynamic ride

heigh t, the amo unt the suspens ion d isplaces when you are

r iding, is actually more important for optimal performance.

As we've d iscussed , static sag is measu red when the mo torcycle

is sta tio nary. D y namic rid e heigh t, as the name would

suggest, is measured w h ile the bike is in mo rio n. Because the

m o torcycle is moving, d ynamic ride height is hard to measure

without data acquisitio n like a Race Tech ShockC lock and

D ynamic G eometry software, but the concepts are important

to understand. Static sag measurements, o n the o ther hand,

are relatively easy to figure our: a ll it rakes is an assistant and

a tape measure.

The main thing preload ad justers do is change the geo metry

of the bike when it is being ridden (see the geometry chapter).

Lee's say the bike is set up perfectly. !fa heavier rider gets

on the bike, the preload ad justers can be used to co mpensate

for the increased weight. If the p reload is nor changed , the

bike wo u ld sag mo re- bo th statically and d ynamically­

when in use. T h is would affect gro und clearance as well

as rake and trail o n the fro nt end and an ti-squa t on the

rear. Prelo ad d oes affect bottoming res is tance, bur if you are

experiencing bo tto mi ng and the sag is in the recommended

ballpark , you probably are no t going to cure the problem

with preload. If the rider weight change is excess ive, the

sp ring rate shou ld be changed.

20 kg more force available to resist bottoming

\ \

~~ --~ ~

----_...----- ,

--~ -----_ .....

~

LL

Cl 40 ,......--- \\ -~ [ 20 kg preload force V -\. --~ - ~~\ -~ -- l the spring is the same, l _ ...

spring rate is .5 kg/mm ---

c 'i:: Cl.. en 30

20

10 --- -0 0 10 20 30 40 50 60 70 80 90 100

Fork Travel (D) mm. 2.11 This graphically displays the effect of preload. The curve is displaced vertically upward. Notice the spring rate (slope) remains the same. In order to get 20kg preload force we had to put on 40mm preload on this .5kg/mm spring. Notice the x-axis is now labeled Fork Travel not Spring Travel.

19

100

90

80

70 en

..:.:: - 60 u.. Q) c..:I 50 ... Q u.. en 40 c ·.: =-(I) 30

20

10

0

Ei tensioh ~ompr1 ssion / /

. v Cll [ 1.0 mm/kg sp~~ "' / ~ en

~ :;:: ) v V"'" "' ~ .... en

/ v

~ ~ v v---both springs

/ ~ deliver 35 kg of I-

force at 30 mm

~ of fork travel /

v---"'

;) ~

~ ~ v --'{ 20 kg preload force ]

~ / ~

• - _J 5 kg preload force ]

- • 0 10 20 30 40 50 60 70 80

Fork Travel (D) mm.

~m~kg spring ]

90 100 110 120 130

2.12 In the graph the .5kg/mm spring has 20kg preload force from 40mm preload while the 1.0kg/mm spring has Skg preload force from Smm preload. Notice they both ~ create the same force to hold up the bike al 30mm travel. z a: Cl.. (I)

MEASURING STATIC SAG THE RACE TECH WAY At first glance, measuring static sag seems pretcy simple.

Excend the suspension and measure becween the axle a nd a

near-vertica l point o n the bodywork/frame o n the rear of a

motorcycle or che exposed chrome o n che front end. Have che

rider get o n che b ike and bounce the suspension several rimes,

then take another measurement. The difference becween che

cwo measurements is the static sag.

Unfortunately, this process will nor get you any cype o f

consisten t measurement. The culprit? Friction.

Friction is o ne of the chree forces in suspension. All

m oving parts in a suspension system have friction . On front

suspensio n , fo rk t ubes slide ch rough bushings a nd fo rk

seals slide over fork cubes, all creating friction. Friction is

present in the rear suspensio n as well. Swingarm bearings,

shock linkages, rear shock seals, and internal pis tons a ll

have friccio n.

T here are cwo cypes of friction: scacic and dynamic.

Static friction is che friction that must be overcome co iniciace

suspensio n movement. Static friction is easy to demonstrate.

Scand nexc co your motorcycle, ho ld the front brake, and

slowly load the fra nc suspension chrough che bars. Notice

that ic doesn't move right away. le cakes a certain amount

o f downward fo rce to get the fo rks co move. Once chey just

sca re co move, che scacic friction of che sea ls and bearings has

20

been overcome. D ynamic frictio n , o n che o cher ha nd, is che

resistance encountered during motion. D ynamic friction is

cypically less chan static friction.

All this fr ictio n creates prob lem s in suspension

performance as well as when measuring sag. If the previo us

method fo r m easuring sag is used , che measurement will not be

repeatable because each time the rider sits o n che motorcycle,

che suspension can scop ac a different positio n (wichin a certain

range). Fortunately we can isolace the effect of the friction

and remove ic from the results using che "Race Tech Mechod."

Instead of using just cwo measu rements (fully extended and

rider o n board), we wi ll take three. T he fo llowing procedure

wi ll give you more accuracy and consistency.

Length One (LI) is the first measurement. To obcain

Ll , che rear wheel must be off che ground. If che bike has a

centerscand, chis cask is simple; if nor it may help co have a

few, friends around co lift the bike. If you're measuring a road

race bike, do n'c use a swingarm scand-even chough the cire

will be o ff the ground, the weight of the motorcycle will sti ll

be pushing down o n the suspensio n, causing it to compress.

Fo r che rear suspension m easurement, use a measuring

cape o r a Race Tech Sag Master co measure che dis tance

becween the wheel axle and some point d irectly above it o n

t he bod ywork o r frame. To measure che franc suspensio n,

the distance becween the axle and lower trip le clamp o r

the exposed chrome length can be used. T his value is the Ll measurement.

(These same locations wi ll be used for all three measurements . Use a tape measure that reads in millimeters, as it is much easier to do the math when ca lcu lating static sag.)

T he L2 measurement is next. Put the motorcycle back o n the grou nd and place the rider on board . Have the rider grab onto something to balance o r use a wheel chock, like the Condor Pit-Stop, while the rider is in position. Now push down o n the suspensio n about 25mm (about a n inch) a nd very slowly let the suspension rise back up and stop. If there were no fr iction in the suspension, it would continue to come up further. Where the suspension stops is the L2 measurement (measure between the same two points as L l ). Ir's important that the rider does not move or jiggle around as this will cause the L2 measurement to be inaccurate .

W here the rider is positioned on the motorcycle is critical when measuring static sag. On off-road bikes the rider should be stand ing on the footpegs for consistency. If the rider sits o n the sea t, there is no telling where he is going to plop his butt down, and this will throw the numbers off. On street bikes, have the rider sit down in a normal riding position.

Now lift the sp rung mass of the motorcycle up about 25mm a nd very slowly let it sink back down until it stops. W here it stops is L3. Again , if the re were no fric tion, it would drop a bit more. The mid point between L2 and L3 is where

it would be without friction. Next average L2 a nd L3 and subtract that result from LI to find static sag. Static Sag =

L 1 - ((L2 + L3)/2) If you carefully use this three-step method to calculate

sag, you will be consistent within one millimeter every time. In

addition to obtaining an accurate sag measurement, the three­step measuring method provides other valuable information about the suspension's condi tion (see Stiction Zone).

Recommended Sag Measurements

Front

Road Race Street

What's the idea l sag? It depends o n the type of motorcycle and rider prefe rence. O ur res ting shows the ideal sag is about 1/.1 to Yi of the suspension's total travel. Typically fo r a sportbi ke, sport-touring, o r s tandard motorcycle, sag should be around 35 mm, fron t and rear. Road race bikes may have less sag, usually between 25-35mm . Some cruisers and custom motorcycles wi th limited suspensio n travel could have 25mm or less, especially in the rear. Off-road bikes, with their much longer suspension travel, are between around 60-75 mm on the front and 95-105mm at the rear. Race Tech, however, has used numbers anyw here from 85mm to l l 5mm on the rear, dependi ng on what kind of geometry is needed. Off-road, 80cc minis can have 55-60mm a t the front and 75-80mm at the rear.

Keep in mind that these numbers have come from testing and are very general. Each setup must be speci fic to the bike and rider.

FREE SAG Free sag is the amount the bike compresses from fully extended under the bike weight o nly-without the rider o n board. T his measuremen t, also known as bike sag, is used primarily du ring rear shock se rup.

If there is too much sag in the suspensio n when maximum spring preload is used (you run out of preload adjustment range), a sti ffer spring may be needed . Similarly,

if rhe preload has been reduced to its minimum and rhere is srill too lirrle sag, it may indicate you need a lower spring rate. But, supposing the range of preload adjustment allows the sag to be in the ballpark, how can you tell if the spring is close to the correct spring rate? C hecking the free sag can help.

For example, if we ser the static sag on the rear of a dirt bike to I OOmm and then measure the free sag to be 5mm, what would we do? The sag chart below says the rear free sag for a dirt

Dirt -full size Dirt - mini 80cc

Sag 25-35mm 30-35mm 60-75mm 55-65mm

Preload 5-25mm 10-35mm 3-15mm 3-10mm

Stiction Zone 5-15mm 5-15mm 10-25mm 10-20mm

Rear

Sag 25-35mm 30-35mm 95-100mm 80--85mm

Free Sag, Top-out Bumper 2-8mm 2-8mm 15-40mm 10-25mm

Free Sag, Negative Spring 10-15mm 10-15mm

Stiction Zone 2-Smm 2-Smm 2-5mm 2-Smm

These guidelines are good starting points and are not set in stone.

21

en Cl z a: Q... en

c: 0 ·;;;

"' ~ "'" E 0 .. c: 0 ·;;; c: ., ... ., preload adjuster

middle position preload adjuster lower position

bike should be l 5-40mm, so we are o ut o f the recommended

range. Wo uld we need a stiffer o r softer spring? T he answer is

a stiffer spring but with fess preload. This is because rhe o riginal

spring is too soft and we cranked in an excessive amount of

preload to get the static sag in rhe ballpark. T h is excessive

preload is ho lding rhe bike up when the rider is o ff the bike. As

you can see, suspensio n setup can be co unterintu itive until you

understand the physics involved.

Keep in mind that free sag should be measured w hen the

static sag is alread y set. In o ther wo rds, if the static sag is way

o ff, rhe free sag doesn't mean much.

Note: T hese are good starting points. T hey are no t written

in stone!

Lately there is a trend for suspensio n manufacturers to use

lo ng, soft, to p-out springs. In bo th fo rks and shocks these are

called negative springs and they fight rhe main spring. Top-out

springs will skew the free sag numbers. To further complicate

things, keep in mind chat m any different rates and lengths o f

top-out springs have been used by suspensio n manufacturers.

If they a re very stiff, the free sag numbers will be very

simi lar to a standard elastomer o r rubber top-out bumper.

If the negative spring is very, ve ry soft , it may be similar to a

top-ou t bumper as well if it completely tops o ut with just the

spring preload . When the negative spring is lo ng and fai rly

soft, it will have a measurable effect.

Put yo ur bike o n a center o r chassis stand , ho ld o nto

the chassis, and push down on the swingarm at the axle with

yo ur foo t. If it extends 5 o r 1 Omm, you've go t o ne o f these

shocks (or else the swingarm is so flexible you should swap it

o ut for something stronge r- li ke spaghet ti noodles). I f you

22

preload adjuster high position

2.13 This figure shows the relationship between spring preload and sag. II also illustrates how changing preload changes the percentage of the suspension's travel that is available for compression and extension.

have determined you have a bike with a negat ive spring and

it has a sig nificant effect, then use the free sag guidelines fo r a

negative spring in the cha rt o n page 2 I .

In general, suspension sho uld not top out under rhe b ike

weight o nly (zero free sag). One exceptio n fo r rhe no- top-out

ru le is when setting up shocks for ad ults riding pit bikes like

KLX l l Os . They are co mmo nly topped out under their own

weight because o f the face chat the bike is fai rly light compared

to the weight of the rider. Some o f these riders can be well

over 200 po unds o n bikes o rigi nally designed fo r kids.

STICTION ZONE The difference berween the L2 and L3 is an indicatio n o f the

amount of frictio n presen t in the suspension compo nents.

We call it rhe stictio n zone. T he size o f rhe stictio n zone is

an excellent indicator o f the co nd itio n o f the suspensio n.

In general, the difference in the measuremen ts for a

properly functio ning fro nt suspensio n is 10- 20mm. If the

m easurement is mo re than 40mm, there is a sig ni ficant

problem . T his cou ld be caused by bent fo rk rubes, worn-out

compo nents (fork tubes, bushings, seals), o r a misaligned

front fo rk caused by improper installa tio n o r a crash. See the

chapter on troubleshooting fo r mo re informatio n.

G ood numbers for rear suspensio n are much lower-2mm

is considered good and mo re than 6mm indicates somerhi ng's

wrong. Excessive frictio n in the rear suspensio n could be

caused by a dirty o r worn-out shock linkage o r swingarm

p ivot bearings, o r a bent rear shock shaft o r bad seal. The front

suspensio n's srictio n zone is greater than the rear's because of

the basic design of telescopic fro nt fo rks. Even when rhe bike is

just sining on ics wheels, there is a side load (accually forward load) on the fork bushings cha t tries co lock up che forks. Added co chis is che relatively large area of the fork seals.

If you have mo re than the recommended sticcion, stop, do no t pass GO, do no t collect $200, and give some accencion co your suspension components.

Luggage should also be taken in co accounc. If a backpack o r fanny pack is used, its weight must be presenc for accurate sag measurements. T he fuel-ca rrying capacicy of che motorcycle is also a consideration. Gasoline weighs arou nd seven pounds per gallon, so the amount of fuel presenc during sag measuremencs will make a d ifference-especially on a dual-spo rt motorcycle with an oversized fuel tank. Testing with half a tank of gas is a good compromise. Rear ax le position can also affect these measurements. Be sure co check sag afcer gearing changes.

SETTING PRELOAD Seccing preload on a shock is preccy straightforward. Referring back co Figure 2.1 0, start by measuring the spring free length, installing the spring on the shock and tightening the spring preload collars un til the set length is shorter chan the free length by che amo un t of the preload.

Telescopic fo rks can be a liccle more involved. T here are cwo structural scyles o f forks: righ t side up (conventio nal) and upside down (inverted). T here are cwo basic designs of cop­o ut springs: incernal a nd external. T he fi rst thing you must

know is which rype of rap-out spring you have. Damping rod forks are always external a nd right side up. Upside down fo rks are always incernal cop-out car tridge forks.

T he only uncertain design is a right-side-up ca rtridge fork as it could be either. T his is easy co determine when the

Suspension Free Length

I2

Push Down, Let Up Slowly

fo rk is apart by looking fo r the cop-out spring location. If the fo rk is cogecher, unscrew che fo rk cap. Ho ld the lower slider and pull up on the fork cap. If it is springy, it has an internal cop-out. Ifie is no t springy, it is an external cop-out. This cype should be springy when you pull up on the ch rome cube.

External top-out. Figure 2.1 5 shows the external top-out spring in chis right-side-up dam ping rod fork. T he easiest way co measure preload is to hold che chrome fork cube in che soft jaws of a vise. Unscrew the cap and lee it rest on che spring or spacer. Measure from the top of the chrome cube co the sealing lip on che cap (the part of che cap chat will scop on the top of the cube). T his is a direct measurement of preload. Make sure che preload adjuster is backed out all che way before you do chis.

Internal top-out. T his rype requires you co measure the set length. The set length is the installed length of the sp ring wi ch the fork fully extended. First, se t the preload adjustment to minimum (if available).

Measu ri ng the se t length is best accomplished with the cartridge out of the fork, however, it can be done with the fo rk spring o ut and cap unscrewed fro m the outer tube but still attached co the damping rod. Collapse the fo rk cube. T he set length is measured from the point che spring touches on the cop of the cartridge to the point the spring couches o n the cap wich the rod fully ex tended. (Sometimes the poinc the spring touches on the cap is actually a special washer o r spacer.) A tape measure can be put down the fo rk cube with

the spring rem oved , if you are careful ro make sure the tape is resting on the flange when measuring.

O nce the set length is recorded, measure the length of the spring and subtract. If the spring is longer than the set length, chis is che preload. Be sure to include spring washers.

Pull Up, Let Down Slowly

Average 310 mm

340 mm 300 mm 320 mm

Length 1 = 340 mm Length 2 = 300 mm Length 3 = 320 mm

2.14 This shows the RT method of setting sag. The Stiction Zone is the difference caused by friction when pushing down to get L2 and pulling up to get L3. The Stiction Zone can give you clues as to whether there is a problem with the linkage or suspension components.

23

en C!I z a: Cl... en

External Top-Out Spring Internal Top-Out Spring

2.15 To setup spring preload the first thing you must identify is which type of top-out spring you are dealing with. Shown are the two styles. Pay particular attention to the method of measuring preload. Another variation of internal top-out spring design is a negative spring. See figure 2.16.

If additional washers need to be added, make sure they are

located properly. This can be done with a flange o n a special washer or spacer or by putting them on the bottom of the spring on an upside down fork.

RELAXED PRELOAD Back-in-the-day life was easy. Measuring preload was simple (Figure 2. 15). All you d id was measure the free length of the spring and subtract the set length to calculate preload.

Life is harder now (tell Mom and Dad). T he latest development for sport bikes is "long, soft, top-out springs" aka "negative" springs as in Figure 2.1 6. This means when you install the spring, the fo rk o r shock gets longer or "grows". If the set length grows, the amount of preload you calculated using the previous method is incorrect (the actual installed preload is less than calculated)!

In the old days the top-out sp ring was so stiff the fork barely grew at all , so we didn't have to accou nt for this. W hat to do, what to do?

Let's define some new terms:

• relaxed set length-the measured installed length without the spri ng installed (easy to measure)

• relaxed preload-the calculated preload using che relaxed sec length (easy to calculate)

relaxed preload = free length - relaxed set length

24

• actual installed set length-the length of che spring installed (can be hard co measure)

• actual preload-the length the spring is compressed from its free length when it is installed with the suspension fu lly extended. (hard co calculate because che accual sec length has grown)

actual preload = free length - actu al insta lled set length

One way to deal with chis is co measure che growth of che cartridge when che spring is installed and subcracc chis amount from che calculated relaxed preload. Wich che spring our, che fo rk cap on, and the fo rk cube fully collapsed, measu re from the cop of che fo rk cube co the fork cap. I nscall che spring and measure che distance between chese same two points. The d ifference is che growth .

When getting preload recommendations from che DVS valuing section on Race Tech's website, we give relaxed preload

because ic is much easier. We usually give a note in the Product and Valving Search co noti fy you char you are dealing with long soft cop-out springs. T he difference can be as much as 40mm!

In most cases we recommend replacing the stock "long,

soft, cop-out springs" with our Reactive Spring Series. They are not as sti ff as che o ld days bur are no t nearly as soft or as long as che new fangled ones. Testing has shown che proper top-out spring can d rastically affect traction particularly when leaned over in che cu rns.

free length

1

~ ~ ~ ~

note the length of the top-out spring

relaxed preload

actual pre load

+ +

relaxed set length

growth

compresses when main

+

spring is installed

installed length

2.16 Forks with soft top-out springs get longer when the fork cap is installed. We have coined the term "relaxed preload" to indicate the amount of preload that would be created if the for1< didn't grow. Actual preload is the installed preload.

RIDER WEIGHT

When measuring sag and adjusting preload, both the rider's weight and the weight of his/her riding gear must be taken into account. The rider must be wearing all his riding gear. Typically a road racer's leathers could weigh as much as 35 lbs. A motocross racer typically wears 10-20 lbs. of

gear, and street riders could be all over the place.

25

Chapter 3 Damping When i rcomes to overall ride and handling characteristics,

many p rofessional runers consider damping ro be rhe most critical factor. Ir's a complex subject, so we' ll start with the basics. Damping is viscous friction. Ir turns kinetic energy in to hear and is sensitive only to damper velocity and nor suspension stro ke positio n. T his makes ir funda mentally different rhan a spring, which stores energy and is only sensitive ro the position in rhe stroke.

Damping in modern motorcycle suspension components is created in different ways, bur it almost always involves a fluid. The configuratio n can be as simple as forcing o il through a hole-as with o ld-style dam ping rod fo rks-or can be as sophisticated as a multi-stage, bending shim stack configuration in comb ination with externally adjustable, low­and high-speed compression and rebound circuits.

All forms of damping accomplish one thing: they slow down rhe movement of rhe suspensio n. Compression damping slows down rhe suspension as it co mpresses when rhe wheel encounters a bump, and rebound damping slows

the acrion of the suspension as the suspension extends.

DAMPING AND ENERGY As we d iscussed previously, springs store energy as rhe wheel encounters a bump. When traveling down the back side o f the same bump, rhe spring releases this same amount of stored energy. Damping, however, changes the kinetic energy o f suspension movement into hear. Because energy can only be changed from one fo rm to ano ther (Newtonian physics­ler's leave quantum physics alone for now), the total amount o f energy remains the same.

T his conversion of energy fro m one fo rm into another is easy to observe. When a motorcycle is ridden over bumps it is rhe damping action rhar causes rhe shock to get ho t. Suspension damping converts energy into hear only when the suspension is moving.

POSITION AND VELOCITY Le r's look at what happens when a wheel hits a bu mp. I nirially the t ravel starrsou tat the static ride heigh tat zero suspension velocity. W hen the wheel hits the bump, the suspension co mpresses. Somewhere the middle of rhe stroke rhe compression velocity is at its maximum and then slows down to zero velocity at maximum compression. T he suspension continues to com press even slightly past the crest of the bump. T he fron t wheel goes airborne and, when it is done compressing, the suspensio n starts to extend. Ir accelerates to a maximum rebound velocity and then slows down to zero at fu ll extension.

26

It remains at zero velocity at fu ll extension unti l the wheel hi ts the ground. I r then accelerates to its maximum ve locity and slows down to zero at maximum compression. Ir rebounds a bit slower this rime, because the wheel is in contact with the ground instead of free falling in the air. Ir overshoots on rebound a bit then fi nally compresses back to the static ride height a nd zero velocity.

SUSPENSION OIL One important factor rhar affects damping is oil o r suspension fluid . Oil is incompressible (well, no r really, bur ro a great ex rent we can think of it rhar way) . When pressu re is applied ro a chamber filled with oil, rhe pressure is exerted equally in all directions. If there is a n opening for rhe o il to get our of a chamber, there will be flow and viscous friction (damping o r resistance ro flow). The degree of damping is determined in large part by the flow rare-more damping means less flow and vice versa.

O il viscos ity is a measure of a fluid's resistance to flow. Ir

is commonly thought of as equivalent co the fluid 's thickness (sometimes called "weight"). The more viscous the oil, the more resistance there is to flow.

O ne measurement of o il viscosity is called Seconds Saybolt Universal (SSU) or Saybo lt Universal Seconds (SUS). Ir is named after Edward Saybolt who arrived at his method to measure o il viscosity around 1898. H e rook 60cc of o il , placed it in a specific var, and heated it to 2 l 0 degrees Fahrenheit. H e then opened a calibrated hole at the bottom and timed how lo ng it rook to drain out.

The Saybolt Seconds measurement ind ica tes the number of seconds it too k to drain: the thic ker the o il, the longer the rime, and vice versa. When a specific o il is measured , it wi ll have a specific number ofSaybolr Seconds: 75, for example.

When the Society o f Automotive E ngineers (SAE) got together, they decided it would make more sense to create viscosity ranges: rhar is 5W, ! OW, 20, 30, and so on.

This method of measuring o il viscosity is actually a measureme nt of kinematic viscos ity. (For the purposes of th is book it is no t importa nt to get into a discussion of absolute versus kinematic viscosity.)

In the SI System (In ternational Sys tem of Unirs­betrer known as me tric) kinematic viscosity is commonly measured in cenrisro kes (cSr). The ISO (In ternatio nal Organization fo r Standard ization) has grouped o il viscosities in to ranges labeled as the mid poin t of the ra nge, that is 22, 32, 46, etc.

compression velocity

zero velocity

rebound velocity

bottom out

E E = 0 -en 0

race sag 0..

top out Time

high compression

en --E no motion > = u

0 Ci) >

high rebound

Time 3.1 This motorcycle hit a bump or jump, went airborne, then landed and recoiled. When it initially hit the bump, the compression velocity spiked then slowed down and stopped. It rebounded to full extension until it landed and the compression spiked again, this time to maximum. It then rebounded again and settled in to somewhere close to the static ride height.

Oil viscosiry changes with temperature. Oil thins o ut as ic

heats up and thickens as ic coo ls. The viscosiry index is a num ber

chac cells us how scable che viscosiry is wich cemperature: che

higher che viscos iry index, the mo re scab le ic is.

T he viscosiry index is determined by measuring che

viscosiry at two cemperacures, 2 10 degrees F a nd I 00 degrees F. T he I 00 degree reading is where the "W" (or "winter")

designacion is measured. (Contrary co popular opinio n, "W" doesn't mean weight.) T he viscosiry index number is the n

assigned based off chese cwo measuremencs. In engine o il

cermino logy, if the oil falls into the I OW range ac che low

cescing cemperature and a 30 range ac the h igh cemperacure, ic is designaced as a I OW30 oi l and is called "mulci-grade."

Oil can be made more temperature, stab le using viscosiry

index modifiers, including cercain lo ng chain polymers. You

can think o f some of these long chain po lymers as looking

like sp iders with lo ng legs. W he n the o il is cold, the spider

legs are wrapped around their bodies and their presence does

27

0 l> s: ..,, z C)

not affect the resistance to flow. When the o il heats up, the

spider legs expand and increase the resistance to flow. T his

causes the o il's viscosity to become thicker than it would be

withou t the viscosity index modifier added.

For example, if we start with a l OW unenhanced

petro leum-base o il, it has the viscosity of a 10 weight at 100

degrees F. If we heat the oil to 210 degrees F, i t is thinner and

is still a 10. We could call i t a lOWlO at this point. But if we

add viscosity index modifiers, this same oil can become as

thick as a 30 at the higher test temperature ( 10W30).

In viscosity index nu mbers, the petroleum-base, straight­

rate, u nenhanced o il has a viscosity index o f around 100 .

T he example o f a 10W30 has a viscosity index of about

140. Engineered synthetic oi ls commo nly have a viscosity

index well over 150 without additives. W ith viscosity index

modifie rs, it can exceed 400.

T he base o il is th in , but the viscosity index modifier adds

to the viscosity. As the o il wears o ut, the lo ng polymer chains

break. Ir's like having the spider legs chopped o ff, and the multi­

grade o il starts to revert back to its base oil properties (in the

case ofa 10W30, it degrades to a straigh t lOWl O or 10 weight).

T his degradation of the viscosity index is one reason suspension

o ils have to be changed periodically. T hese oils also suffer

contamination from internal wear (adding things like aluminum

oxide) as well as external contamination past the seals.

As mentio ned previously, standard o il viscosity ratings

are ranges, no t specific viscosities. This means oil viscosity

ratings can vary within a range between manufacturers. A 2

weigh t oi l from o ne manufacturer mig ht actually be thicker

than a 5 weight o il from a different company. Trying to

compare suspensio n o il from different companies is futile

unless you actually test them. T his is co mpounded by the

fact that suspension oils are not governed by the same

laws of classificatio n that engine o ils are-suspensio n o il

m anufacturers can call their oi l anything they want. For these

reasons it is impo rtant to choose a brand and stick with it fo r

consistent resu lts when making internal changes.

W hich o il is the best oi l to use for motorcycle suspensio n?

After much testing with various manufacturers, Race Tech

eventually had its own Ultra Slick suspensio n fluids b lended

back in the mid-1990s and has continued to refine them over

the years. T hese fluids use synthetic-base o il alo ng wi th high­

end frictio n modifiers. T hey are very slippery, temperature­

stable, retain thei r viscosity index fo r a lo ng time, have high

thermal oxidatio n resistance, and provide a lo ng service life.

MEASURING DAMPING Let's take a closer look at damping. As we discussed earlier,

damping is sensitive to damper shaft velocity. A spring is easy

to measure, but how can we measure a damper? Imagine we

have a really long shock: ho ld it horizonta lly, p lacing the end

of the shock o n a scale resting against a wall, then compress the

shock at a steady rate. The scale in our scenario would indicate

the am ount of damping being created at that velocity.

If we then increase the rate of compressio n in increments

and reco rd the corresponding damping in a table, we could

plot these damping numbers against the different velocities.

Fo r this example we have arbitrarily defined compressio n as a

positive velocity and compressive fo rce as positive. For rebound we would have to replace the scale with a

pull scale. We could then start the process over, measuring

rebound damping at incremental velocities. To plo t this data we wo uld recognize that extensio n is a negative direction

and rebou nd damping force is negative. Next we would

3.2 Making damping the old-fashioned way! In reality a shock dyno is used to cycle the shock rapidly while taking data at a very high rate.

28

50

40

30

20

= .lll: 10 -u. 0

Q) (..) ... Cl -10 u.

-20

-30

-40

-50 t -.5

1 1 l l "O - - "C "O ~ - "O Q)

"' Q) Q) Q)

"' Q) Q) Cl. Cl. Cl. Cl.

"' "' "' "' .r:: :;:: :;:: .r:: .~ - - 0 0 >--- - .~ .r:: - - .r:: -- T

~ ~ .A•

./~~:-transition from low speed to -D high speed damping is not

_..,- . .....

a line, but rathe r a zone ....... .......... 2) compression -~ velocity is maximum

....--4,-- J '§::'. 1) shaft velocity r~rt at mid-stroke .,Av I starts at zero \\

) ~ ~ !L l1\ ) 5) shaft velocity _ v reaches zero again at

/ f ~ maximum rebound

3) shaft velocity reaches V zero again at

I f( maximum compression

4) rebound velocity .#' is maximum - ----" ~

~at mid-stroke I

-.4 -.3 -.2 rebound (- )

-.1 0 .1 .2 .3 .4 compression(+)

Velocity(V) meters/second

.5

I-

3.3 This is a damping curve going through one complete cycle. Notice the curve starts from fully extended al zero velocity then accelerates as it compresses-going lo the right- up to a maximum velocity (in this case .5m/sec). It then starts slowing-retracing the curve back lo zero velocity at full compression. It changes direction and starts rebounding up to a maximum rebound velocity at mid-stroke of .5m/sec then retraces the rebound curve as ii slows down to zero again at full extension.

50 mm

50 mm

------------------------------------f --

50 mm

------------------------------------f --

3.4 Bump shape is critical in the creation of damper velocity. The more square-edged it is, the higher the compression velocity will be created, everything else

being equal. Notice also, that the smaller the wheel, the higher the damper shaft velocity.

29

connect the do ts, as in Figure 3.3, es timating the rea l cu rve by smoothing rhe data. T he combination of the smoothed compression and rebound curves is the total damping curve .

Real shock dynos typica lly use a crank on an e lectric motor, hydraulic cylinder, or linear electric motor to stroke the shock in and out. They measure velocity and load at very high sampling rates. In one full cycle of the shock it starts o ut at zero velocity, compresses to a maximum ve locity, slows down and stops, reverses d irection, sta rts ex tending up to a maximum rebound velocity, then slows down to zero. This gives us a lot of data in a single cycle. O n the graph this cycle starts at the origin (0 velocity, 0 fo rce) . Ir heads up the c urve to a peak then heads back down to the o rigin. I r then goes to a maximum rebou nd velocity a nd heads back again to 0, 0 (origin).

In actual use the entire damping curve (the full measured range) is not used on every bump. If the maximum velocity of a particu lar compression hit is very low, it doesn't go up the compression curve very far. On the rebound side, energy is stored in the spring, so the fu rther it is compressed, the faster the maximum rebound velocity will be.

W hen tuning the suspension damping, it is viral to know wha t velocities are occurring. Particu larly on compression, the shape of the bump has as much to do with the velocity as the size of the bump. Bumps can be square-edged, rounded, ramped , or somewhere in between. The more square-edged

a bump is, rhe fasrer rhe suspension musr move ro allow rhe wheel to travel over the bump while keeping the tire pressed on to the road's surface. Even at a relatively slow vehicle

speed, riding over a square-edged bump creares a grear deal of velocity- consider an aggressive parking lot speed bump that abuses you at relatively low speeds.

Conversely, a rounded bump will cause the suspension to move more slowly as seen in Figu re 3.5. Bump shape aside, as vehicle speed increases, so does the suspension velocity. Double the vehicle speed and you'll double the shaft velocity. (Well, not exactly; there are other factors like tire

compression, but you get the idea.) You may no t have the luxury of a ShockC lock or other data acqu isition system, but it is a good idea to start estimating whether the actual velocities are low or high speed.

How much damping is best? Well that depends on how you're rid ing, w here you're riding, and what type of motorcycle we're talking about.

Sometimes the answer is counterintuitive. Most peo ple

think that racers (both MX and road race) need more damping than trail riders or street riders. T hink abouc the back side of

the bump when the wheel is trying to get back on the ground: rhe faster you a re going, the quicker it needs to extend. This means we could actually benefit from less rebound damping at higher speeds. Hmmm ...

In fact, when magazines evaluate a new sportbike at a racetrack, they often wri te something like: "We wanted to lay down a really hot lap at Wi llow Springs, so we added a bunch of

30

compression and rebound damping to help control wallowing at the high speeds." While this definitely controls wallowing, there may be a much greater price paid in traction. When Race Tech technicians provide suspension support at the track, they find that many racers use way too much damping, and as soon as dam ping is reduced, their lap times improve.

Let's turn to d irt applications. Supercross requires bo ttoming resistance as a primary consideration, par ticularly fo r lesser-experienced riders that overshoot o r undershoot land ings. SX whoop sections also benefi t from a fairly high level of compression stiffness to maintain chassis geometry and help a rider "get on top of the bumps." Though it helps in the whoop sectio ns, this high level of stiffness is cou nterproduc tive on braking a nd acceleration bumps. Many tuners feel that a lot of rebound damping is also beneficial, but there is really no reason to have more than that required fo r ou cdoor MX.

Mose current sporcbikes have external adjustments fo r bo th compression and rebound damping, as well as for sp ring preload. Many fo rks use a screw adjustment located on the top of the leg fo r rebound damping (not to be confused with the spring preload adjuster). Another screw o n the bo ttom, near the axle, usually adjusts compression damping. Sometimes two adj ustments are provided fo r low- and high­speed compression damping.

A few street bikes use one fork leg exclusively fo r

compression damping and rhe o rher exclusively for rebou nd damping: these will be labeled as such. T he side used fo r compression damping usually has the lerrers "Comp" stamped on the fo rk cap. Rebound damping is indicated as " Reb," o r often as "Ten" which is short for rension.

Mose modern dirr bikes with twin chamber forks have

the adjusters reversed. The compression damping adjustment is on che rop of the fork legs a nd rebound adjustment is on rhe bottom. T he main poinr is chat it's very important co check

Most cartridge forks have the rebound damping adjuster on the fork cap. It will often be labeled with the letters "Ten" (tension) or "REB" (rebound). A few models, such as the 2009 Yamaha R1 s, FZ1 s, and many Moto Guzzis, have one fork cap for compression and the other for rebound.

50

40

30

[ compression(+) ]

---~ ~ -->----->---bump shape J

20 r high displacement, ,, ,,

[ but low peak velocity ,, ,, ,,

= 10 .lll: -u.

0 Q) (.) ... Q -10 u.

-20

-30

\ ,, ,, -

\ -~ - ----

.,,....--/

v /;'

/ v

/ high displacement .-:._ means higher peak

1" ..r I

rebound velocity

-40 I

I

-50

I rebound (-) ] I I

-.5 -.4 -.3 -.2 -.1 0 .1 .2 .3 .4 .5 Velocity(V) meters/second

50 I I I

40 [ compression(+) J

l ~ ~

I .. -30 >----->--- bump shape J

,, 20

= 10 .lll: -u.

0 Q) (.) ... Q -10 u.

,, I high peak velocity, ~ ,, ,, ,, low displacement J ~ --~

.,,....-v -~ .,,....---IC _,, -~~ ,,

,," -20

,, low displacement ,, means lower peak

-30 ,,

rebound velocity I I

I I

I

-40 I

I

-50

I rebound (-) ] I , I I

-.5 -.4 -.3 -.2 -.1 0 .1 .2 .3 .4 .5

Velocity(V) meters/second 3.5 This illustration shows the effect of the shape of the bump given equal bike speeds. Notice the bumps are the same height as well. The ramped bump will not create as high of compression velocities as the square-edged one. This is shown by the compression not climbing up the compression damping curve as far. On the rebound stroke this shows the effect of the wheel deflecting off the square edge on compression causing ii to use less travel. Less travel used means less energy stored in the spring, so lower peak rebound velocity will result.

31

for these markings o r consult the owner's manual before you

start making adjustments. On rear shocks, the adjusters on the reservoir typically

are for com pression and the one on rhe shaft near the eyele t is fo r rebound damping. These adjusters-often referred to as "cl ickers"-have their limits and typically affect only a small portion of the entire damping ra nge. Tweaking external adj usters will never make up for poor internal va lving.

Most external rebound da mping adjusters adj ust low­speed damping. If there is only one compression adjuster, it is usually low-speed. If there are two compression adjusters, o ne is low-speed and the ocher is high-speed. Making external damping adjustmen ts can never compensate fo r worn-ou c damping components o r worn-out suspension o il. So, if your bike is wallowing like a '62 Cadillac with blown-out shocks, you might wane to do some suspension rebui lding o r replacement before you spend the rest of your li fe playing with the clickers.

, , , , ,

, , , , ,

, , , , , , ,

, , , ,

, , ,

maximum traction

, , , ,

, ,

useful range of adjustment

.. , , .. ..

REBOUND DAMPING Let's cake a closer look at rebound damping. Cha nges in rebound damping affect trac tion, the feeling of contro l, and ride plushness. If you look at Figure 3.6, you will see chat all o f these facto rs are plotted .

First lee's look a t p lus hness. W ith less rebound damping, the wheel moves quickly and the ride quali ty is plush even to the po in t of being " loose." As rebou nd is increased, the feeling of plushness drops off until, at the extreme end, the ride feels harsh.

Notice chat there are no numbers o n either axi.s, as the purpose of the graph is to communicate the concept. Also, the feeling of control is largely subjective, so it is hard to assign numbers co. Having said that, these charts are based on years of testing both on- and off- road machines and hold true in theory for virtually every type of vehicle. Keep in mind most riders do n't ride at the limit of traction, and if you're no t at the limit of

traction, it can be quite d ifficult to cel l if you've lost traction.

.. - -­....

maximum feeling of control

......... ~ ... , e~ .

' ~ ',~~

\~ \ C:O

\ ~ \ ""' \ ~ \ \ \ \ \ \ \ \ \ \

less (qu icker)

Rebound Damping more (s lower)

3.6 This shows the relationship between rebound damping and traction, control, and plushness. Note that when traction is falling off as rebound is increased, the feel ing of control is still increasing. Most riders will beneM from using less rebound damping than they are used to.

32

Looking at the graph, you will notice that with too little rebound dam ping, there is very li t tle traction ava ilable. W hen the tire hits a bump, the suspension compresses and the spring sto res some of the energy. O n the back side of the bump, the stored energy in the spring pushes the ti re back down in a n unconcrolled way. The ci re is free to osci llate and can become so light as it bounces that it literally comes off t he ground. Undamped oscillation is the enemy of tractio n. If the motorcycle is traveling in a straight line, the loss of t raction will me rely be uncom fo rcable . However, if this happens when the bike is leaned over in a turn , the loss of t raction can cause the bike to slide ou c and crash .

Similarly, with an excess of rebound damping there is very lit tle traction available. In this case, as che tire travels up the bump the spring is, again , storing energy. T his time, however, when the tire attem pts to move dow n the back side of the bump-p ushed by the scored energy in the spring­the movement is slowed down excessively by the rebound da mping. If the action is slowed enough, rhe ti re will no c be ab le ro fo llow rhe downside of che bum p fasc enough ro main tain consistent con cacr with the ground . T his will cause a reduc tio n or complete lack of cracrion .

W hen suspension wirh roo much rebound dam ping encoun ters a series o f bum ps, ir can lead co packing. T his means the suspensio n doesn't return fa r enough, not reaching irs original srarcing poinc. T he availab le travel ro absorb

bumps becomes less and less, and ar rhe same rime ir requires more and more fo rce ro in itiate movement. T his can reduce t raction as well as make fo r a harsh ride.

Now lee's suppose the init ial rebound sercing is already ar rhe peak of traction. lf we increase rhe rebound da m ping and rhe rest rider has a leisu rely pace o n a racetrack or th rough a canyon, rhe resu lting loss in traction may nor be recognizable. However most riders will feel li ke there is more control.

Most riders believe char a bike is in control when rhey

don't fee l ic wiggling around in rhe corners. Less wiggles fee ls like more traction, and more wiggles feels like less t raction.

l e is imporcanr ro note on rhe chart char rhe point ar wh ich rhe bikes feels rhe most "in control" is nor when ir has rhe

highest amount of rracrion. Therefore, ar rhe point of highes t traction, rhe bike will wiggle around a li ctle more rhan fee ls

com fortable fo r many riders. T he main reasons why rhe point of maximum feeling of

control and rhe point of maximum rracrion are so far aparc for both dire and pavemen r riders is because most riders are no r riding on rhe "edge" of tractio n. And second ly, mosr don't

relate decreasing rebou nd damping wirh improving traction. For d ire, rhere is also rhe symptom of " kicking." Ir is

rhe most commonly misdiagnosed problem o n rhe rear end. I r is rhoughr ro be a lack of rebound da mping while in face ir is usually caused by either excessive stiffness or excessive bottoming. So rhe bike kicks and, ro fix ir, rhey slow rhe rebou nd. The rider will li kely chink rhe " kicking" is solved, and especially if rhe rider is prone to chinking char slowing

the rebound will cure rhe problem . T he rider never recognizes char he lost tractio n and gets used to the new feel. And, in face, any less damping than ch is will make the bike feel "loose" ro him. T he rebound is never sped back up: after all why would anyone want ir ro "kick" again ? Hmmm .. .

O n rhe paved end , many srreec riders and road racers "resr" rhei r suspension se ttings on perfec tly smooch roads char hardly even need suspension. In such a scenario, an overabunda nce of damping provides rhe least amount of wiggling, add itio nal pi tch contro l (fron t ro back movement), and, fo r chem, the maximum fee ling of control.

T he job of rhe suspension engineer and tu ner is ro make rhe rwo peaks-max traction and max fee ling of conrro l­as close as possible. This is done by reshap ing rhe damping curve and requires an understanding of high- and low-speed damping. H owever, some riders are so used to excessive rebound da m ping, you likely will never ger rhe two curves ro peak ar rhe same poin t.

So where do you want ro set rebound? Some would say where rhe curves cross, buc th is is nor a measurable point. The useable range is between the two peaks. If rhe setting is ro rhe lefr of rhe traction peak, you lose borh rracrion and the feeling of co ntrol. If yo u are ro che right of che feeling of control peak, you are losing borh traction and control. Now, if rhe rider can gee used co a little looser feeling, the gains in rracrion will improve lap rimes and rire life, and his " ideal

feel peak" would be closer ro the rraction peak. Some riders

cannot hand le rhe looser feeling and end up closer ro rhe control peak.

Sometimes it's possible ro "see" d iffe rences in traction o n

d irt bikes. By trying different rebou nd settings in rhe same corner (particularly one wirh poor tract ion) you may notice a d ifferent level of roost coming off rhe rear t ire. T he rider must

use rhe same line and rhe same gea r and enter rhe corner ar rhe same speed as much as possible. W hile many chink a big roost looks li ke traction, rhe opposite may actually be true.

Go back ro our earlier discussion of energy. Energy is rhe abili ty to do work and can be changed from o ne form to another. Power is rhe rare of doing work. T he power created

in rhe engine has ro go somewhere: ir can be turned into either projectiles or propulsion. Marhemarically: P = P + P or Power= Projecti les + Propulsion (si lly bur true) .

All kidding aside, rhe message is imporranr. After a cercain point, mo re dirt flying off rhe back cire means less accele ration for rhe vehicle, and vice versa. Keep in mind char

being in too low of a gear-particularly on an open bike­will cause rhe wheel ro sp in and throw up quire a roost. T his

may look and sou nd fast bu r in fac t is qu ire che opposite. A word of caution: be ing ar rhe limi t of rraccio n is a

delicate position ro be in , and ir is often nor possible co cell any diffe rence in cracrion wirhour pushi ng rraccion co ics lim it. U nder chese circumstances ir's easy ro go roo far and crash. Keep in mind rhac d ifferent brands or models of tires react d ifferently at che edge of traction. Some are very fo rgiving and

33

some go away abruprly. W hile resting, ir is vitally important to keep in mind that while slowing rebound down you might be giving up traction .

We know that too little rebound damping and too much rebound damping can be equally bad when ir comes to both traction and a fee ling of control. At the ve ry least, the optimum range of rebound se ttings is somewhere between the peak of traction and the peak of the fee ling of con trol. W hile there is no owner's manual that can tell you where to set the ad justers for maximum traction, tes ting to find this setting can be qui te rewarding.

HOW TO TEST REBOUND DAMPING So how do yo u find the po int ar which the rebound dam ping settings will provide maximum traction ?

T he first method isa "push tesr."T his test requires that the sp ring se tup is in the right range. Also, iris vical chat friction is minimal: if the suspension suffers from an app reciable amount of fric tio n, this tes t is worthless. (Telescopic fo rks o n rhe fron t end are notorious for excessive friction, so be aware.) T he push rest can be very useful, bu t it may require q uire a bit of testing to get the fee l of ir.

We' ll discuss how to rest the rear suspension, but the procedure is basically the same for the fron t. Stare by measuring sag, paying particu lar attention to che "scicrion zone." If sticrion is excessive, you will not be able ro use ch is method.

Stand next to rhe mororcycle with rhe fronr w heel poinred straight ahead. Push down on the sear fai rly aggressively and warch what happens when rhe suspension rebounds, o r moves

upwards. Ler you r hands fo llow che sear as it comes up: this means you are not holding it down nor are yo u letting your hands completely o ff che sear. You are looking for rwo things: how fas t rhe suspensio n rebounds and che number (if any) of bounces chat ic rakes just after it reaches rhe cop of its stroke.

Too much rebou nd damping looks like rhis: you push down on the seat and you can see che suspension move upward slowly. As ir slowly reaches che top of rhe rebound stroke it stops all movement.

Too licde rebou nd dam ping looks somewhat different: you push down and rhe suspension rebounds nearly as fas t as yo u can remove your hands. In addition to a qu ick upward movement when it reaches rhe cop of irs s troke, it moves back down again and oscillates two or more times.

Here is what a good starting point for rebound damping looks like: after rhe suspension is compressed, ir will rebound. W hen the suspensio n reaches rhe rop of its stroke, ir will barely overshoot and settle down to irs free sag point (a very sma ll, single bounce) .

Keep in mind you can o nly feel low-speed rebou nd da mp ing with this resr and nor high-speed.

If friction is excessive, ir wi ll appear that there is more rebound damping rhan there accually is, and this resr wi ll be misleading! A considerable number of vehicles out there have so much lin kage or bearing frict ion chat yo u can li rerally cake

34

all rhe oil out of rhe shocks, life up the wheel, and it wi ll s tay whe re you place it. In chis case rhe fr iction feels very simi lar to dam ping and can fool you. T his is where a measurement of the stiction zone can be invaluable.

Another rh ing that can change the feel is the stiffness of the sea t. If the seat is soft, the compress io n will fee l softe r and the rebound will feel slower. You may want to fi nd something harder to push on, like a rail section. Using the tail sectio n instead of the sear will give you more leverage and rhe sp ring and compression damping wi ll feel softer. H aving said this, if you do enough push tests and correlate chem with crack testi ng, you can get quite good at initia l setup.

The second, and best, way to adjust rebound dam ping is to go testing and make a series of runs with different rebound adjustments. Create a bracket of settings by changing the adjustment in one direction until ir gees worse. Then go in the o ther direction until it gets worse. If you do this, your setting in the midd le was the best. But remember: if you are not o n the edge of traction , you may no t be aware of the change. T his is not easy. As yo u are testing, pay attention to how che feeling of control changes and select a setting chat gives you the balance yo u like.

O n some bikes with adjustable rebound damping, you can change rhe se ttings and work up co this point. Nor all rebound dam ping adjusters are equal, however. On some motorcycles the range of adjustment is too fa r o ne way or the

ocher. For example, sometimes when rhe rebound adjuster is ser ro rhe maximum (slowest) setting, the resulting rebound

damping is still roo qu ick. T his is quite commo n on street fo rks particularly in the 1990s and ea rly 2000s. On dirt bikes it is just as commo n ro see rear shocks with roo much rebou nd dam ping even ar m inimum se ttings. T his is a tellcale sign the suspensio n needs co be modified interna lly. Vircually all motorcycles can benefi t from afcermarker valving and personalized setup.

If you own a motorcycle without rebound dam ping adjustment, you may still be ab le to make it better simply by changing rhe o il. As we discussed previously, most oil's viscosity will break down with use and the oil will beco me th inner, o r less viscous. This is quite often overlooked. It's also worth noting here char rear shocks on some bikes a re not rebuildable and therefore cannot have their o il changed.

Because you may not know what weight to pu t in (s tock weights may not be viscous enough, or in some rare cases, too viscous), a q uick check ar www. racetech.co m will usually provide the inform ation. Unfortunately, while increasing o il

viscosity may improve rebound damping by slowing it down, it will also increase compression damping. T his may resu lt in excessive co mpression damping, bur forcunacely there are fixes for this.

Remember that externa l rebound adjusters are typically low-speed adjusters. Eve n if yo u gee a good setting fo r traction using them, there may be huge gains to be had from internal va lving changes as well. Noc only is it poss ible to move the

peaks closer together, you can also improve concrol when

using large amo uncs o f travel- li ke o n big bumps o r whoop

sections in the d ire-or make improvemencs in pitch control,

particularly o n the fro nc end o f a street o r road race b ike.

COMPRESSION DAMPING Compression damping is o ne of the most misunderstood

compo nencs o f suspensio n rnning. Understanding

how compressio n damping affects ride quali ry goes a

lo ng way toward demystifying the "b lack arc" of how

suspension works.

A fundamencal difference exists between compression

a nd rebound damping. Compressio n dam ping has to deal

wich a much wider range o f velocities generated by bumps o f

differenc sizes and shapes. Rebound damping, o n the o ther

ha nd, primarily has to concro l the energy o f the compressed

sp ring and , therefore, its adjustmencs are easier to perform.

Compression velociry-and therefore damping-is

affected by the shape, as well as the size, of the bump as well

as the speed at which you hit it. Bumps that have a more

square or sharp-edged shape cause the suspension to move

rapidly upward, while a bump with a gradual s lo pe, o r more

rounded shape, causes slower suspension movement. This

is the reaso n for separate low- and high-speed compression

damping. Rem ember, the terms high- and low-speed damping

useful range of adjustment

refer no t to the forward speed of the motorcycle, but rather

the velocity of the suspensio n movemenc.

In the past, many suspensio n tuners have considered

compression damping a necessary evil, meaning that less was

bercer. Perhaps this way of chinking stems from che limitations

o f old-sryle damping rod forks. D amping rod forks have what is

known as "orifice-sryle" damping, which can be bo th too harsh

and too mushy at the same time. (More o n this in a mo ment.)

W ith the ad vent o f cartridge-rype fo rks found on most

spor tbikes and Race Tech Gold Valve Cartridge Emulators

(aftermarket damping control valves fo r damping rod fo rks),

the ability to control the shape of the compression-damping

curve has improved dramatically.

To study the effects o f compressio n damping we' ll fi rs t

loo k at compressio n damping as a whole and leave the derails

of high- and low-speed fo r later. Compression damping

is virally impo rtant as it affects traction, p lushness, and

bo ttoming resistance as well as con trol. (See Figure 3 .7 .)

Lee's first consider bottoming resistance as it relates to

plushness . Notice that the mo re compression damping there

is, the mo re resistance the suspension has to bottoming out.

Compressio n damping force is added to the sp ring fo rces

to help resist bottoming. Ar the same rime that bo ttoming

resistance increases, the feeling of p lushness decreases making

the ride harsher.

less (softer)

Compression Damping more (stiffer)

3.7 Notice that, as with rebound damping, both traction and control drop off as compression damping is increased. It doesn't fall off as rapidly as with rebound. Notice also that the peak for control is lo the right of traction once again.

35

As compression damping is decreased (left side of the graph), plushness increases up co a poinr. In extreme cases, when very little compression damping is used, the plushness can actually decrease. T his occurs on big bumps when the suspension bottoms and feels harsh. In this case many riders are not aware that the harshness is a result of bottoming. In fact, I would estimate only 50 percent of riders {even really good ones) can tell if the front end bottoms and only 1 in 20 can tell when the rear is bottom ing.

On smaller bumps, less damping results in a plusher ride. It may seem obvious, but you need co have the right amount o f co mpression damping-not coo much, nor coo little. Bottoming resistance and ride plushness are a compromise. You may need co sacrifice one fo r the other. T he job of a suspension designer/tuner is co have the least amount of compromise in both areas. More on this later.

So, more compression dam ping means more bottoming resistance: pretty simple. But the creation of dam ping requi res velocity, so in a situation like bottoming mid-turn on a road racer where there is very little suspensio n velocity (the suspension is being compressed due to centripetal acceleration), compression damping is not the answer co this particular bottoming problem- springs are.

Let's examine the effects of compression damping on traction. Imagine you're riding along and you hit even a small bump. If there is coo little compression damping, the

suspension will noc have enough resistance co upward wheel movement. This means that the wheel sti ll has vertical inertia at the crest of the bump, so it wi ll continue co move upward. Remember Newton's First Law of Motion: "Every object in

a state of uniform motion tends co remain in that state of morion unless an external force is applied co ir." As the wheel conrinues co move upward, it conrinues compress ing the

suspension past the crest of the bump. This causes the ti re co unweighc and possibly even lose contact with the road surface as it crests the bump, causing a loss of traction.

Ac the ocher extreme, excess ive compression damping will give coo much resistance co suspension movemenr, thereby compressing the cire and deflecting the sprung mass upward. Noc only can chis cause an uncomfortab le or harsh ride, hu e chis upward velocity of che chassis unweighcs the wheel, just

like having coo licde compression damping. In extreme cases o f coo much compression damping and a large or square­edged bump, the wheel comes entirely off che ground as it skips over che bumps, causing a dramatic loss of traction.

In bumpy turns at extreme lean angles, you may experience difficulty holding a line as the bike wi ll cend co d rift co the o utside of che turn due co the loss of traction.

If you're hitting a series of bumps with coo much

compression damping, the suspension can actually pump up as che wheels hie successive bumps. This is the opposite

o f packing caused by coo much rebound damping. As che traction curve shows on che graph , traction fa lls off much more quickly with coo much compression damping. So if you

36

have co guess how much compression damping co use, err o n the side of coo little.

Dive is a term used co describe the fronrend compression that occurs d uring braking. In th is case, compression damping controls the race of downward movement. The maximum amount of travel used in the forks is determined by a combination of the spring force (includ ing air pressure) and the com pression damping (a lo ng with friction of course). More damp ing makes the forks compress slower and may use less suspension travel. Less compression damping causes the forks co compress faster and use more suspe nsio n travel.

O ne of the biggest misconceptions abou t compression damping is that che fas ter you ride, the more you need. It is true chat the faster you go, the harder you hit bumps­yo u may need more compression damping co control bottom ing. It is also true thac some racers that are more abrupt wich the application of the brakes and the throttle may prefer a slower compression response race. H owever, if yo u are not boccoming and you can learn co apply the brakes and chroccle more smoochly, you may not need any more compression damping.

Our preferred method is co first determine proper sp ring rates {see che spring chapter or the charts at www.racecech. com) and then use only as much compression damping as you need fo r pitch control (rocking of che chassis fronr and back

during acceleration and braking) and borcoming conrrol. Keep in mind that the shape of the damping curve is

critical. In chis section we simplified our description of symptoms and talked about damping as a whole, but in real life the bike may need more low-speed damping and less high-speed co achieve the best setu p (or vice versa). The

compression side is what good tuners spend a lot of their time on-they're always seeking che right curve to maximize

bottom ing resistance while maintaining plushness and provid ing a good "feel" fo r the ground.

HOW TO TEST COMPRESSION DAMPING U nlike rebound damping, it is hard co push the suspension down fas t enough by hand co cell a Joe about compress io n damping. Therefore, you will need co find a su itable road or section of dire co use fo r cescing. Idea lly ic will have boch large and small, rounded- and sharp-edged bumps on it.

When there is coo much compression damping, yo u wi ll feel the bike hiccing che fronr sides of bumps somewhat like the way a suspensionless bicycle reacts when it hies bumps. The ride will also feel harsh over moderate and even small bumps. Keep in mind, however, chat excessive fr iction or binding can feel the same way.

In che case of coo licde compression damping, che front end wi ll tend co dive qu ickly under braking {lack of pitch co ntro l) . le can have an overa ll mushy or vague feel and may boccom ouc easily. If che suspension boccoms excessively on che front side of a bump, it can lau nch che bike and rider in co

the air. This can feel like excessive compression damping- it can be very difficu lt to te ll the difference. More informatio n o n this discinccion is available in the croubleshoocing chapter.

On a d ire bike ic can be valuab le co wacch che roosc o ff the rear wheel. If you have a rough scraighcaway wich che type of d ire rhac will show a visible roosc, wa tch fo r an even scream coming off the back wheel as the bike is ridden over the bumps. If the roosc stares and srops, ic is no r maintaining t raction. Ofcen, chis is because the compression is too stiff and the suspension is deAecci ng. This can also be caused by a too sofc compression se tting. Nexc make a change in che directio n you think is best and see ifit gets bercer o r worse. Remember, too, that rebound damping can cause this phenomenon.

Another clue o n dirt bikes can be gathered with your ears. O n a rough, choppy section, listen for evenness of the engine. If the rpm are going up and down a lot, the wheel is not o n the ground much. T he two most likely reasons are that it may be deflecting off the bump because it is too stiff, o r it could be skipping over the bumps because che rebound is too slow.

Personal preference has a lo t co do with the " idea l" setup, as some riders like a firmer ride wi th more bottoming resistance while others li ke it plusher. It is noc abouc right o r wrong, it's just personal preference and what will make thac rider the fascest they can be.

DAMPING ROD FORKS (ORIFICE DAMPING) We've d iscussed compressio n and rebound damping,

includ ing what each does and why they are necessary to main rain traction. Now we'll move on to the various types of

fork and shock designs that are used to control da m ping. T he most common fork design is the damping rod. I know,

I know: damping rods? W hy damping rods? If you understand damping rods and their limicacions and solutions, it will be easier to understand cartridges. Once you understand cartridges, it will be easier to understand shocks. This way, once we get to shock design, it won't take much effort to cover the subject.

Damping rod forks have been around fo r years and coday can be commonly found o n most cruisers, standards, trail bikes, dual-spores, minis, and mosc vintage bikes. D am ping rod forks are less expensive to manufacrure but don't offer

much sophistication in the way of damping control.

DAMPING ROD ANATOMY Figure 3.8 shows che components of a damping rod fork design. T he fo rk slider at che bottom is attached to the motorcycle's fro nt axle and the fork rubes are inserted into

the upper and lower trip le clamps. Inside the forks are the springs and damping rods. T he main fork spring is located di rectly on top of the dam ping rod char is fastened ro the fork slider with a bolt ac the bottom. T he main spring supports the sp rung mass of che fro nt of che motorcycle and rider. T here is another smaller spring called a top-out spring located between the bottom of the damping rod and bottom of the fo rk rube. T he top-out spring keeps rhe fork rube fro m banging into the

Fork Cap

0-Ring

Washer

Preload Spacer

Fork Tube

Washer

Ai r Volume

Main Spring

Oil Level

Dust Seal

Snap Ring

Oil Seal

Bushing

Damping Seal

Top-Out Spring

Rebound Damping Orifice

Bushing

Check Valve Passage

Rebound Check Valve

Damping Rod

Oil

Fork Slider

Compression Damping Orifices

Damping Rod Bolt

3.8 Damper Rod Components

damping rod as the fo rks extend full y. Most modern dam ping rod fo rks use a top-out spring.

The top of rhe damping rod is a pisto n and has a pisto n ring chat sea ls on rhe inside of the fo rk ru be. The piston ring keeps suspension o il fro m passing between che damping rod and che inner fork rube.

37

0 l> s: ..,, z C)

DAMPING ROD COMPRESSION STROKE W hen che fork is compressed (Figure 3.9), you can piccuce che fork cube (the upper poccion) moving downward in to chamber A. T he volume of oil displaced is chac which che fo rk cube displaces. (This means che wall thickness, noc che ou cer d iamecec o r inner d iamecer.)

As che fork compresses, che volume in chamber A is geccingsmaller while che volume in chamber Bis geccing largec. T his means che o il pressure in chamber A increases while che pressu re in chamber Bdecreases. H owever, as soon as movemenc

38

check valve opens on compression stroke to easily fill chamber "B"

occurs, che rebound check va lve opens and allows fluid to pass easily inco chamber B. T his means che pressure in chamber B is only slighdy less chan in A, and you can pcaccically consider chambers A and B to be one chamber (AB).

At this po inc, che vo lume the fo rk tube displaces scill needs to gee ouc of ch am bee AB. le escapes ch rough che compress io n damping holes locaced ac che boctom of che damping rod, up ch rough che cencer of the dam ping rod, and ou c into chamber C . l c can also cravel ouc chrough the rebound hole(s) in chamber B, buc this is a much smaller vo lume.

3.9 Damper Rod Compression Stroke Notice the check valve separating chamber A from chamber B is open offering very little resistance to flow.

this orifice acts as a bleed hole on compression stroke

compression damping orifice restricts flow

Compression damping is concrolled by che number and size of che compression damping ho les and che rebound dam ping hole(s) along wich che oil viscosicy. Noce chac che rebound holes accually reduce che overall compression damping caused by che compression holes. This cype of da mping is refe rred co as o ri fice-scyle damping because che resiscance is creaced by forci ng o il chrough holes.

Ic is also imporca nc co noce chac che pressure in chamber C builds as che air volu me decreases. This pressure in cha mber C is dependenc o n che inicial pressure, che compression racio (oil level), and the travel.

A5 long as che compression scroke is noc too rapid, o rifice damping can provide a reasonably comfortable ride as che from wheel h ies small bumps. Unforcunacely, noc aU bumps are rounded and small in size-when a square-edged o r large bump is encouncered, o rifice damping can creace a very harsh ride. Because oil is noc compressible, che fascer che fork com presses, che fascer che oil is fo rced ch rough che compression damping holes.

O rifice-scyle damping increases very rapid ly as velocicy increases. In face, che dam ping fo rce increases wich che square of che velocicy. T his means every ci me che velocicy doubles, che damping increases by four rimes. We have illuscrared ch is (see Figure 3. 10) by showing che chick flow arrow being squeezed ac che en crance of che small orifices on a high-speed hie.

You can see che compression scroke d isplayed on a shock dyno graph in Figu re 3. 11. Nocice chac as che speed builds, che fo rce builds. T his happens slowly ac fi rst but chen increases rapidly before going nearly vercical. Ir is almosc as if the o il flow-and cherefore che fo rk velocicy- reaches a speed limi c. T his is no c absolucely crue, of course, buc because the dam ping fo rce becomes very high, che maximum velocicy che fo rk reaches, in praccice, becomes limiced. This causes che wheel co deflecc off of square-edged bumps and che ride gees harsh, indicaced by che curves going inco the "pain zone."

Another drawback of o ri fice damping occu rs in che low-speed range of movemenc. W hen braking, che fra nc

if orifice damping is set up to be

~~=i~=~ firm at low speed, :==~~ it will be harsh at high speed.

if orifice damping is set up to be

!J::::F=~~==: plush at high speed, :==::::::=~~ it will be mushy at low speed.

3.10 The down-side of orifice damping is it is either too mushy and soft at low speeds or way too harsh on high speed hits.

39

Cl) c.:I .... Cl u.. = c c. E ~ c c Cl en en Cl) .... c. E Cl (.)

Velocity 3.11 This figure displays damping curves for four compression hole sizes. Notice the characteristic "fish hook" shape remains for all the curves. Notice also the tradeoffs involved.

end dives rather slowly in com parison to che high velocities

crea ted o n an abru pt hie of a square-edged ho le o r rock a t

high vehicle speed. Ac chese low dam per velocities chere is no r

much resistance to flow and che forks feel mushy and dive

rela tively rapidly. In face, when going ch rough long du ratio n

dips or gu llies-even if chey are nor very deep-che fo rks

can bottom .

Perhaps you've considered increasing the compression

damping ho le size as che so lu tion for che harshness problem.

T his change in orifice size is illuscraced in che compression

dam ping curves in Figu re 3 .11. Nocice char the characceriscic

"fish hook" shape of che curve remains. W hile less "mushy,"

the smaller hole wil l be excessively harsh o n the square-edged

hi es. T he larger damping hole will be mush ier, tho ugh ic will

be beccer ac high speed. T his scyle of damping seems to provide

che worse of boch wo rlds-harshness and bo ttoming.

Nore also char oriflce-scyle dam ping doesn't require

rou nd holes. Any fixed orifice will do: square, triangular, oval,

and so on.

DAMPING ROD REBOUND STROKE Now we'll take a look at the flow of oil when the fo rk rebo unds

(see Figure 3.12). First the forks extend as che spring pushes

o n the damp ing rod. T he rebound check valve then closes

and chamber B gees smaller, raising its pressu re on rebound

to the highest level in che fork. There are two ways oi l can gee

40

ou t of chamber B: fi rst th rough the rebound orifices routed

to che inside of the dam ping rod and , second, between the

inner d iameter of the check valve and the oucer diameter of

che damping rod directly into chamber A. Rebo und damping

is che resistance to this flow.

C hamber A on che other hand, is getcing larger o n the

rebound stro ke, and therefo re has che lowest p ressure. T hi s

low p ressure in chamber A causes o il to be sucked back in,

refilling ic.

Jusc like on che compression stroke, rebound resistance

on a damping rod fork is created through o rifice damping.

Rebound dam ping, however, is a much simpler jo b than

compression damping. Rebound o n ly has to con trol the

fo rce of che fo rk sp ri ng, whereas compressio n damping

has to deal wich whatever fo rces che road or crack d ish out.

Maximum compressio n velocities o ften range fro m two

to six times greater than those during rebound. Thus the

limitatio ns o f o rifice damping are less critical for rebound

than fo r com pression.

A major pocencial problem of a damping rod fo rk is

cavitatio n (see Figure 3.13). Cavitation is the fo rmation of

vapor bubbles in a flowing Liq uid caused by a decrease in

pressu re. This occurs specifically in areas where the pressu re

of the liquid fa lls below its vapor pressure. T his is che same

pheno menon as boiling, bur in th is case ic is caused by a

decrease in pressure rather than che addition of hear.

check valve closes on rebound stroke

T hiscreares rwo problems. First, irmakes rheo ilcompressible

because ir con rains vapo r bu bbles o r "voids," rhereby decreasing

rhe oil's d am ping characteristics. Seco nd , when rhe void in rhe

o il rapidly collapses, ir p rod uces a shock wave rhar can d amage

and pit rhe su rface of rhe parts (this second issue is much more

o f a problem in shocks rhan fo rks) . The po ten tial fo r cavitation

increases at lower pressu res and higher temperatu res.

On rhe rebo u nd stroke, chamber A is getting larger and

sucking o il back in to ir. T he grea ter rhe resistance ro flow is

ar rhe com p ressio n o rifices (smaller ho les or th icker oil), rhe

3.12 Damping Rod Rebound Stroke The check valve is shut. This means chamber B is a high pressure chamber and rebound damping is created by the flow out through the rebound holes and the clearance between the outer diameter of the damping rod and the inner diameter of the check valve.

rebound damping orifice restricts flow

leakage past check valve

grea ter rhe potential for cavita tio n . Stiffer springs and ho rrer

o il a lso increase rhe po tential p roblem .

THE PROGRESSIVE MYTH This brings us back to rhe age-old q uestio n: "H ow do you

make ir firm a nd plush ar rhe same rime?" M os t suspensio n

tu ners have believed char rhe solu tion was ro m ake ir mo re

progress ive. Perhaps you 've no ticed rhe shape o f rhe o rifice­

sryle dam ping curve and tho ught ro yourself: "W o w, char

cu rve is rea lly p rogressive!"

41

In fac t, o rifice-style da m ping is the most p rogressive type

o f d amping rhere is. Bur w ith the sho rtcomings o f o rifice­

style d ampi ng (harsh ness and bo rroming), you can see rhar

mo re p rogressive isn't necessarily bette r.

Consid er the compress io n d amping cu rve labeled "d igressive" in Figu re 3. 14 . At lo w speed ir has a lo t mo re

com pressio n d amping . This w ill make the action much

fi rmer whe n hi tting the brakes, thereby controlling dive

(rhe fro nt e nd com p ressing du ring braki ng). Ir will a lso help

bo rroming because o n every compressio n stro ke, no matter

42

3.13 This illustration shows cavitation occurring on the rebound stroke when the restriction is too great during refill of chamber A. The effect shows up even more on subsequent strokes.

bubbles are formed by vacuum

cavitation occurs when the orifice cannot pass enough oil

wha t max imum velocity is reached , rh e velocity begins and

ends ar zero . T his means rhe d amper sees low-speed damping

rw ice per stroke, so any increase in low-speed d am ping te nds

ro imp rove bo tto ming resistance.

Also no tice that, a r hig h velocity, t he cu rve d oesn't get into the "pa in w ne." You mig ht th ink, "Yeah, but ir's head ing

there." In actua li ty, there is a max imu m velocity thar rhe

suspensio n sees in the real world . This maximum velocity

is pa rtia lly d epend ent o n the size and shape o f the bumps

being h ir, the veh icle speed , rhe mass of the b ike, and rhe

suspensio n setup. T he highest velocity I've ever recorded o n

the ShockC lock is 15 m/sec on a "sho r t" supercross land ing

(the rider h ie the face, didn't quite make ir) .

Granted , that is very fas t, but it also has some

implications-changes to the damping curve at velocities

over 15 m/sec don't have any practical effec t even in

supercross racing .

GOLD VALVE CARTRIDGE EMULATOR FORK Fortunately for damping rod fork owners, there is an eleganc

way to change rhe shape o f rhe damping curve wirh rhe

addition o f Race Tech Gold Valve C artridge E mulators. I

invenced Emulators back in rhe early 1990s to provide rhe

compressio n dam ping curve o f a cartridge fork, make ir

tunable, and offer ir ar a ve ry reasonable cost.

W ith rhe Emulator, low-speed compression has a much

beccer feeling of control while high-speed compression

absorbs large and sharp-edged bumps without harshness. This

provides rhe rider wirh beccer steering response and causes the

bike to feel mo re planted in the tu rns, yet mo re com fortab le

at rhe same rime.

Yo u can see in Figure 3. 15 char rhe Gold Valve Cartridge

Emulator sirs o n rhe top of rhe damping rod and is held in

place with rhe main sp ring. T he Emulato r perfo rms rwo jo bs:

ir provides a digressive com pression damping curve char is

adjustab le, and separates compressio n from rebo und damping

Q) (,) ... c LL

en c CL

E «I c c c en en Q) ... CL

E c

(..')

so char bo th can be independenrly tuned. Lee's rake a look at

how ir wo rks.

The Emulator rakes over compression dam ping

duties fro m rhe da mping rod. To do ch is rhe damping rod

compression ho les are enlarged and , depending o n rhe model,

increased in number. W ith la rger flow area the restrictio n at

t he compressio n holes becomes negligible. Ir is certainly srill

rhere, bur rhe effect is so sma ll i t is no lo nger significant.

Instead , all the com pressio n damping rakes place in

t he Emulator.

W ith rhe Emulator installed o n top o f rhe damping rod,

low-speed damping is controlled by low-speed bleed ho le(s)

in rhe valve piston (see Figure 3 .15). Oil flows unrestricted

from cham ber A to rhe inside of rhe damping rod , then

up toward chamber C. Ar rhe lowest velocities rhere is nor

enough pressure to open the main valve pisto n and all the o il

goes through rhe Emulator's low-speed bleed ho le .

At higher velocities, particularly when rhe wheel

encounrers a square-edged bump or when landing from a

jum p, rhe fo rks muse move rapidly. The o il pressure builds in

cham ber A and beneath rhe Emulator to a po inr char lifts rhe

Emulator pisto n offi rsseat, allowing rheoil to flow into chamber

C (see Figure 3.16). The o pening pressure is adjustable via rhe

valve's spring preload. C hanging the valve spring rare contro ls

the slope of the damping curve o nce rhe pisto n opens- check

o u t rhe range of adjustment available (Figure 3 .1 7).

Velocity 3.14 Many tuners over the years have erroneously believed that the more progressive the compression damping is the better it is. This style of curve actually gives the worst of all worlds-mushy and harsh. A better solution is a digressive curve for most applications.

43

0 l> s: ..,, z C')

Here is a closer loo k at the details of the Emula to r (see Figure 3. 18). T he m id-speed compression damping adjustment is accomplished by changing the valve spring preload that pushes the piston agai nst the Emulator's valve face. By increasing the va lve spring preload, more pressure is required for va lve opening.

Once installed, making changes is relatively easy. First remove the fork cap and main spring. Use either a long welding rod bent over at the end or a "pans grabber" a nd lift the E mula tor out of the fo rk tube . Adjust the valve spring

44

preload and reinstall. This can be do ne on many bikes with the fo rks still mo unted .

Let's look at rebound (see Figure 3 .19) . Installation of the Emulato r does not change rebou nd damping, therefore, adjust ment o f rebound damping is made by changing the oil viscosity. Though it may no t sou nd like it, this is sti ll a significant cha nge. In a standa rd damping rod fo rk with no Emulator, changing the o il's viscosity will change rebound dam ping, but at the expense of cha nging compression dam ping in a similar way. With an Emulator,

3.15 The Emulator is a compression valve that sits on top of the damping rod and is held in place with the main fork spring. During the lowest compression veloc~ies the damping is created by a small orifice.

low-speed orifice damping is provided by hole in the emulator valve

check valve opens to easily fill chamber B

more and larger holes in damping rod radically reduce orifice damping

it doesn't matter wha t weight o il is used to obtain idea l rebo und damping because co mpression dam ping can be adjusted separately.

So how effective are Emulators? Not only d id Jamie James win the AMA National Road Race Championship in 1994 with a facto ry Yamaha using Emulators, but Lee was part of an endura nce team that won the WERA National Endurance C hampionship in 200 1. T he team had two identical Suzuki SV650s that were ridden by three riders. T he only difference be twee n the two motorcycles was the damping con trols in the front fo rks. One bike used Race Tech Gold Valve Cartridge Emulators on the stock damping rod forks and rhe ocher

mo rorcycle had fu ll carrridge front fo rks. T he lap times were virtually identical between the two seru ps.

Dirt bikes have had similar resulrs. Back when the Factory Suzuki Team was j ust making the swirch ro four-strokes, ir cam paigned DR350s wi th bo th Race Tech carrridges and Emulators. T he feedback from the riders was char bo th were excellenr. Many mini bike, vintage, motocross, and road race championships continue to be won wirh Emularors.

STANDARD CARTRIDGE FORKS Srandard carrridge forks a re more sophisricated rhan damping rod fo rks. From outward appearances, right-side-up sta ndard

3. 16 When the shaft velocity gets high enough, the pressure increases to the level required to open the main valve. Once ~ opens, the damping curve is linear and the rate of increase depends on the valving spring stiffness.

the emulator valve spring can be tuned with both preload and rate changes

supple high-speed damping is provided by opening of the emulator valve

check valve opens to easily fill chamber B

45

-u.. Cl) u ... Cl u.. c Cl en en Cl) ... c. E Cl u

-u.. Cl) u ... Cl u.. c Cl ·c;; en Cl) ... c. E Cl u

gold valve emulator valve spring preload

Velocity (V)

I I i gold valve emulator ] valve spring rate stifler rate

...--,,\ ~_, k:::::

~ ~ ~ ....., ~ ~- 71

~~ ~ __, L_ - softer rate

)

/ Velocity (V)

~ ~ :::::::.-: t::::=---

- gold valve emulator t-+- ---+-----<t---+-- -+-- -+-- ---1

u.. Cl) u ... Cl u.. c Cl en en Cl)

bleed size

~ r---J~::::t~~~l"""~i----j==":i E Cl u

Velocity (V) 3.17 Emulator adjustments of valve spring preload, valve spring rate, and bleed hole size create tremendous tuning flexibility.

cartridge forks look very similar ro damping rod forks, but

the difference is o n the inside.

In standard cartridge forks, the dam ping is done ins ide a

me tal cartridge, hence the name. T he cartridge tube is a ttached

ro the bo tto m of the fo rk leg. T he main spring, located inside

the fo rk tube, sits between the rop of the cartridge and the

fork cap. The drawing shows a small rop-out spring that is

external ro the cartridge.

46

valve

3.18 Emulator Components

low-speed compression damping orifice

check valve

Inside the ca rtridge are two valving assemblies-the o ne

fo r compression is located in the bo rro m o f rhe cartridge. The

va lve assembly that governs rebo und dam ping is located o n

the end of rhe d amping rod ar rhe top. T he ocher end of rhe

damping rod is arrached to the fo rk cap .

Most cartridge forks also have external adjustments fo r

rebo und and compressio n dam ping. T he low-speed rebound

ad justmen t screw is located ar the top of rhe fo rk cap. The

ad justment screw is connected to a long rod that extends down

into the cartridge . T he end o f the rod (or a separate need le)

has a taper char acts as a need le valve, controlling the o il flow

through the low-speed rebo und o rifice. When the adjusanent

screw is turned in (clockwise) the needle is lowered deeper into

the ho le, restricting the flow of o il and increasing damping.

This low-speed adjuster also affects high-speed rebound-as

it con tinues to flow at high speeds-but no t to the extent that

it affects low-speed rebo und.

The low-speed compressio n ad juster is located at the

bo ttom of the fork leg. (On some models the screw is located

o n the side of the fo rk leg.) It works in a similar manner as

the rebound ad juster. We'll take a closer look to see how both

low- and high-speed damping are accomplished, starti ng with

the compression stroke o n a car tridge fo rk.

Let's say the front wheel encounters a small, rou nd­

shaped bump and the fork compresses. Upon compressio n ,

the dam ping rod goes into the cartridge and d isp laces fluid.

T his volume o f oil (rhe volume rhe damping rod displaces)

musr exir rhe carrridge . In a s randard cartridge fo rk it is this

vo lume of fluid thar conrrols compression dam ping.

In Figure 3 .2 1, chamber A is gerring smaller, so ir has

rhe highesr o il pressure . Notice rhat the rebo und check valve

is opened as the fo rk compresses. The check valve creates very

lirrle resis tance ro flow and allows cha mber B ro fi ll easi ly.

T his means chamber B has o nly a slig htly lower o il pressure

than A (norice rhis is very similar to chambers A and B in a

damping rod fo rk). C hamber C has rhe lowest pressure.

Ar very low velociries, all o f rhe flow o ur of rhe cartridge

will pass through the adjustab le low-speed compress io n

3.19 On the rebound stroke the Emulator check valve opens feeding the enlarged compression holes to refill chamber A Rebound damping is created exactly the same way as wijhout an Emulator.

check-valve opens, allowing chamber A to refill easily

rebound damping is unchanged from standard damping rod fork

enlarged compression damping holes reduce restriction to chamber A, reducing cavitation

o rifice. As long as the compressio n srro ke moves slowly

enough, rhe low-speed compression damping circuit in rhe

compressio n base valve will con rrol all rhe flow o f o il.

N ow ler's look at hig h-speed compression. As rhe shafr

veloci ty inc reases, so does rhe resisra nce ro flow rhrough

rhe low-speed adjusrer circuir. T hi s causes rhe p ressure

in chamber A ro increase. At a pressu re determined by

rhe stiffness o f rhe shi m valving stack, rhe shim s deflecr

and the po r t o pens. Note rhar o il still passes rhrough the

low-speed compress io n o r ifice, but wirh h ighe r p ressure,

t he bu lk o f the flow passes rhroug h the high-speed

damping circuir.

47

low-speed rebound damping

needle orifice

cupped washer

check valve spring

check valve plate

rebound damping valve body

seal

check valve port

high-speed damping port

high-speed damping shim stack

base plate & nut

nut

cupped washer

check valve spring

check valve plate

check valve port

seal

high-speed compression damping port

compression damping valve body

high-speed compression damping shim stack

oil feed passages

base plate

low-speed compression damping needle orifice

3.20 Standard Cartridge Fork Components

rebound valve detail

compression base valve detail

In Figure 3 .22 you can see rhar rhe compress io n shi m

srack consisrs o f a series o f special small washers. These small

washers act like springs: as o il pressure exerts force o n rhe

shim srack rhey deflect, allowing o il ro flow past rhem and

o ur o f the cartridge . The ind ividual shi ms char make up

the shim stack can be changed in number, diamete r, a nd

48

low-speed rebound damping adjuster

oil feed passages

top-out spring (external)

bushing/seal

rebound valve

cartridge tube

compression base valve

low-speed compression

damping adjuster

rh ic kness ro conrro l rhe amo unr o f damping. (Ir sho u ld

be no red rhat even rho ugh the drawing shows o il flow ar

t he righ r side of the shi m srack, actual o il flo w takes place around rhe enrire circumfe rence o f the valve. It is drawn

th is way ro illusrrate rwo sets of po r ts, one set flowing in

each d irectio n .)

y~y

c

3.21 Standard Cartridge Fork Low-Speed Compression

:z

check valve open ,

oil passes easily

check valve closed

low-speed movement doesn't create enough pressure to open the shim stack

49

c

3.22 Standard Cartridge Fork High-Speed Compression

50

check valve open,

oil passes easily

check valve closed

high-speed compresion circuit opens when pressure builds enough to deflect the shim stack

REBOUND DAMPING Rebound damping on the standard cartridge fo rk design works in a similar manner to compression damping (see Figure 3.23). As the fo rk extends, the check va lve closes and chamber B gets smaller, making it the highest pressure chamber in the fo rk. Chamber A is getting bigger and therefore has the lowest pressure .

Ar low-speed rebound velocities, there is no t enough pressure to open the rebound shim stack and all the flu id flows fro m cha mber B into chamber A through the low-speed rebound orifice. During low-speed rebound, the rebound adjuster needle contro ls the flow of o il.

During high-speed rebound, the pressure in c hamber B is high eno ugh to open the rebound shim stack (see Figure 3 .24). O il certa in ly co ntinues to flow through the low-speed rebound circuit, bu t the majo ri ty of o il will go through the bending shim c ircuit. Just as with compressio n damping, the rebound shim stack can be tuned by changing the number, thickness, and d iameter of shims.

Let's no t forget the process of refilling chamber A. T he entire vo lume of chamber B gets transferred to chamber A, but this is no t enough volume to completely refill chamber A- it is defic ient by the vo lume of the damping rod. Fo rtunate ly the compressio n damping valve has a check valve that opens , allowing fluid to pass freely from chamber C back in to chamber A.

Ir is bo th in te resting and important ro recognize that the velocity of the rebound stroke is directly related to the amount o f travel used. The more travel used, the more energy is stored in the spring and the greater the force is extending the fo rk. T his typica lly means that low-speed rebou nd damping will be created on smaller displacements and high-speed will be created when lo ts o f travel is used. The exact velocity will a lso depend o n things like whe ther the tire is in contact with the grou nd o r the bike is in the air (probab ly no t with a street bike- I hope) .

MULTI-STAGE DAMPING T here is a va riation on the standard shim stack used in the cartridge fo rk that produces a mo re progressive compress io n damping curve. As you can see in Figure 3.25, the compressio n shim stack has two shim stacks on top of each o ther, separated by a smaller diameter washer. At the lowest velocities the shim stack is closed a nd a ll the flow goes th rough the low speed adjuster. As the velocity increases, the low-speed stack (the o ne closest to the valving piston) opens and oil flows through the compress io n damping holes-the same as a single-stage shim stack.

In the next d rawing (Figure 3 .26) the compression stroke is even fas ter, causing even higher o il pressure in chamber A. With m ore o il pressure pushing on it, the low-speed shim stack is deflected far enough to make contact with the second (high-speed) shim stack, thereby stiffening up the to ta l stack. With two-stage (o r more) shim stacks, the progressiveness

can be tailored. Nore that the more stages there are, generally the more progressive the curve will be. T his style of stack is common on dirt bikes.

D o n't be confused by the termino logy. When we refer to a low-speed and high-speed compression stack, you might wonder if the low-speed adjuster and the low-speed stack control the same velocities. Any time there is an open " bleed" hole, it is the lowes t speed dam ping control. T he po in t at which the low-speed stack opens depends on its stiffness.

Keep in mind that the effects of all of these components overlap. The higher the velocity, the less effect the low-speed adjuster has, though it does sti ll flow and have some effect. We will get in to fu rther derail about va lving stack styles a bi t later in this chapter.

CARTRIDGE FORK MID-VALVES On the com pression s troke of a ca rtridge fo rk, the job o f the check valve on the rebound pis to n is to allow o il co freely pass from chamber A to chamber B. But wha t if we put a valving stack in the place of the check valve and call it a mid-valve? W hat are the possible benefits and limita tio ns?

On the rebound stro ke (Figure 3 .27) it is easy to see there wo uld be no downside to it . Its job is simply to shu t off the flow th rough chose passages, and it would do just that . On the com pression stroke there certainly is flow from chamber A to B, but cham ber Bis getting bigger, so it tends

to crea te a vacuum. If we restrict the flow too much, we

could easily cause the fo rk to cavirate on the com press ion stroke and cause incomplete fi lling of chamber A. If, on the o ther ha nd , we restric t the flow below the level that causes

cavitatio n, we would be adding compressio n damping. W hat's the d ifference be tween adding mo re damping

at the compress ion piston versus adding it to the mid-valve?

Remember that the volume of o il that goes through the compression piston on the compressio n stroke is exactly the vo lume d isplaced by the damping rod . On the compress io n stroke, the volume of o il tha t goes fro m A to Bis the area of the

inner diameter of the cartridge minus the area of the damping rod rimes the length of the displacement. This means that a 24mm diameter ca rtridge with a 12mm diameter damping rod will pass 3 rimes the volume in to cham ber B th rough the m id-valve than out of the cartridge through the compress io n base va lve.

So what is the benefit of the mid-va lve? We have been

talking about o il as being incom pressible, bur that is nor precisely true. Because there is a slight compressib ility of the o il as well as expandabili ty of the ca rtridge rube, the re is a

bi t of a lag between the damping rod entering the cartridge and the da mping being created by o il passing through the compression valve- particularly on very small movements. Because rhe vo lume is so much greater thro ugh the mid-valve, it doesn't ra ke much valving to create a significant amo un t of compression damping. The net resu lt of a mid-valve is rhar the "lag" is reduced.

51

c

3.23 Standard Cartridge Fork Low-Speed Rebound

52

low-speed orifice

"'1!~:::::::=----.--r""'"I creates damping

check valve closed

low-speed movement doesn't create enough pressure to open the shim stack

check valve open,

oil passes easi ly

3.24 Standard Cartridge Fork High-Speed Rebound

check valve closed

high-speed rebound circuit opens when pressure builds enough to deflect the sh im stack

check valve open,

oil passes easily

53

3.25 Standard Cartridge Fork Two-Stage Low-Speed Compression

54

check valve open,

oi l passes easily

check valve closed

low-speed movement generates on ly enough pressure to move the low-speed portion of the shim stack, but not the high-speed stack

3.26 Standard Cartridge Fork Two-Stage High-Speed Compression

check valve open ,

oil passes easily

check valve closed

high-speed movement engages both stages of the shim stack

55

cupped washer

check spring

support shim

primary clamping

shims

refill ports

rebound piston

rebound shim stack

3.27 Mid-valve Components

mid-valve detail

T he mid-valve was first introduced in dirt b ikes. T he

challenge for a mid-valve in a dirt bike is to be able to handle

incred ibly high shaft velocities o n compression . T his makes

for extremely high Aow rates past the mid-valve valving stack

and the shims have to bend very far. In the past there have been

many forks where the m id-valve shims distorted permanently

o nce in use. T his sometimes occurred o n rhe very first ride­

o nce bent, rhey no longer function as a mid-valve. If rhis

happens, why have a mid-va lve in the first place?

T ho ugh there are potential weaknesses, there are also

benefits ro be had if the mid-valve can be crea ted that doesn't

permanently distort and is set up to prevent cavitatio n.

T here are a number of mid-valve designs, bu t lee's look

ar a very commo n o ne. Look at Figure 3.27. T his mid-valve

consists of a shim stack that slides o n a sleeve. This allows

the mid-valve stack ro d isplace before it has to bend. There

is a secondary shim char suppo rts the bending shims a t high

deAections, and there is a coil spring to return the stack back

to the pisto n on the change fro m com pressio n to rebound .

MID-VALVE COMPRESSION STROKE Refer to Figure 3 .28. When the compressio n stroke begins, the

mid-va lve immediately displaces a distance we call the "Aoac,''

"clearance," o r "gap." T his Aoat is provided because o f the

immense Aow rate fro m chamber A to Bon the compression

stroke, particu larly on dirt bikes.

As the velocity increases, the shim stack starts to bend.

(See Figure 3.29.) It bends until it hi ts the secondary shim,

which helps keep it fro m permanen tly distorting. On the

56

travel limit shims

clearance or float

sleeve

a mid-valve is a modified check valve

mid-valve

everything else is the same

rebo und stroke, the entire mid-valve disp laces back ro rhe

pisto n face wirh a little help from the check spring. The

rebo und stack behaves as normal. (See Figure 3 .30.)

In the past I o ften recommended dismantling the mid­

valve and converting ir back to a standard check valve as it

eliminated the potential problems of permanent distortio n

and cavitatio n. Some of the stock designs today have less

problems with permanent disto rtio n , and in these cases we may

recommend no r changing the mid-valve back ro a check va lve.

In other cases Race Tech offers Rebo und Gold Valves

that not o nly have tunab le rebo und valving stacks but also

tu nab le mid-va lves, allowing tremendo us Aexibili ry. Race

Tech HFR (High Frequency Response) Rebo und Gold

Valves fo r pavement u tilize a no n-displacing mid-valve,

so they make the change in directio n from compressio n ro

rebo und very rapidly. T he reason we can get away without a

d isplacing mid-valve on these models is that the compression

ve loci ties are much lower than o n a dirt bike, so the po tential

fo r permanent disto rtio n is dramatically reduced.

Bear in mind that caviration is always a risk- that the mo re

compressio n damping you create at the mid-valve, the higher

t he po ten tial for cavitatio n o n the compressio n stroke. If you're

using a mid-valve and yo u decrease the compressio n damping

o n the compressio n base valve, you increase the chance of

cavira tio n. This is because it is the resistance to the flow through

the compression valve (and our of che cartridge) thac fo rces che

o il fro m chamber A to chamber B. You need to seek a balance

3.28 Mid-valve Low-Speed Compression

3.29 Mid-valve High-Speed Compression

becween having enough compression valving ac the compressio n base valve and no t too much mid-valve valving.

TWIN-CHAMBER AND OTHER PRESSURIZED FORKS AND CAVITATION W ith the ad vent of the mid-valve cam e an increased po tential

fo r cavitatio n. In the old days before che cwin-chamber fo rk, we

used co introduce this subjecc in the shock absorber seccio n of

57

rhe Race Tech Technical Edge Suspension Seminars, bur ch is is

now a big part of fork design too.

As you may remember, cavitatio n is the fo rma tion o f

vapo r bubbles in a Aowing liq uid caused by a decrease in

pressure. T his occurs speci fically in an area where the pressure

o f the liquid falls below its vapor pressure. One way to reduce

the tendency coward cavitatio n is to pressurize the cartridge.

Refer to Figure 3.3 1 number I . H ere we have a shock

shaft artached to a solid piston in a shock body partially fi lled

with o il. T here is a ho le in the piston and the p iston can slide

but seals nicely o n the body. There is no "cop" o n the shock, so

it is open to atmospheric pressu re. Before mo tio n is initiated ,

the pressure in both chambers A and Bare equal at 0 .

If we compress the shock very slowly, the pressure in

chamber B becomes negative (a vacuum) while the pressure

above the piston remains a tmospheric at 0. (It sho uld be noted

char in this example we are using gauge p ressures, not absolute

pressures . Absolute pressure at standard atmospheric pressure is

about 14.7 psi, or I atmosphere. Gauge pressure ac atm ospheric

pressure is 0 psi, o r 0 atmospheres. 0 psi absolu te is an absolute

vacuum.) Ar this very low velocity there is very li crle cavitation ,

bu t with enough resistance chere can be some.

Refer to Figure 3.31 number 2. As we increase che shaft

velocity, che pressure becomes low enough to create voids o r

vacuum pockets in the Auid. T he faste r the shaft is moved,

the mo re cavitation occurs. T he smaller che hole-and

therefore, che greater the damping effecc-che sooner che

cavitatio n happens.

Refer to Fig ure 3.31 number 3. To remedy the problem ,

we could puca Aoacingpiston o n che top of the Au id in chamber

58

3.30 Mid-valve Low-Speed Rebound

A and put a coil spring with preload against the opposite side

of rhe piston. This way the ini tial p ressure in bo th chamber A

and chamber B not o nly start off the same before movement,

but are at a higher pressure. W hen movement is initia ted, the

spring fo rce creates a pressure that helps push the o il through

the o rifice in co cha mber B, thus reducing cavitatio n. If there

is enough initial pressu re created by the spring, cavitatio n

can be completely eliminated . In rea lity this can be a difficulc

so lutio n co assemble, buc ic is used when the pressures required

to eliminate cavitation are fairly low (as in fo rks) .

Refer to Figu re 3.31 number 4. On a shock absorber the

forces are fairly high, so a more practical solution is the use of a

compressed gas instead ofa coil spring co create che pressu re inside

the damping chambers. It is important to note thacwhen the system

is at rest, che pressures in all three chambers (A, B, and the nitrogen

chamber) are the sam e. If che nitrogen pressure is high enough

co overpower che resistance co Aow, cavitation is eliminated . Noce

that as far as eliminating cavitatio n is concerned , ic doesn't matter

whether a piston or a bladder is used in the reservoir.

Lee's go back now co the front fork. Look at Figure 3.32.

If we want co pressurize the cartridge, we need co make room

for a pressure chamber. If we mount the cartridge upside down,

we can attach the damping rod co the bo rco m of the fork. The

cartridge rube and compressio n valve, alo ng with the reservoir

piston, are then attached co the fork cap at the top of the forks.

Notice chac che shaft chac the compressio n piston is

attached to is the sam e o ne che reservoir p iston slides on. Yo u

can see that che reservoir is pressurized with a coil spring.

This illuscracio n is based o n a Showa Twin-Chamber.

Some detail is omitted, buc no tice the necked-down part of

low pressure pulls oil through damping orifice

pressure helps fo rce oil through damping orifice, reducing cavitation

3.31 Cavitation Control

the compression damping shaft just below the fork cap-it

is marked as "assembly groove." This is Showa's solu tion fo r

assembly, and we will discuss the details lacer in the book.

Briefly, w hen the cartridge is initially assembled, it is overfilled

with o il. The d amping rod is then compressed a ll the way,

displacing the reservoir piston and comp ressing the pressure

high shaft velocity creates high damping and strong vacuum causing cavitation

high pressure eliminates cavitation

spring until it reaches the assembly groove. Ar th is point the

reservoir pisto n shaft seal no lo nger seals and rhe reservo ir

p iston stops moving u pward. Any excess o il " leaks past."

W hen the shaft is released , the pressure spring extends and

the reservoir piston moves down and seals again, trapping rhe

correct amo unt of oil inside the cartridge.

59

low-speed compression

damping adjuster

assembly groove

compression damping rod

reservoir pressure spring

reservoir piston

compression valve

compression damping rod

cartridge tube

rebound valve

rebound damping rod

top-out spring (internal)

shaft seal

oil passages

spring

low-speed rebound damping adjuster

3.32 The Twin-Chamber design inverts the cartridge and adds a spring-pressurized reservoir. The value of a pressurized cartridge is it can eliminate cavitation if there is any.

60

As to the functio n of the fork, the damping is exac tly the

same as a standard, no n-pressurized cartridge. O il is forced

through the compression valve and moves the reservoir pisto n

because of thedisplacemen to f the dam ping rod into the cartridge.

T he reservo ir provid es pressure to eliminate cavitation.

It is interes ting to no tice that with this p ressure-sp ring

design , the pressu re in the cartridge starts very low, as the

pressure spring preload is very low. T he pressure bui lds as the

fo rk compresses. This means the resistance to cavitatio n starts

ve ry low and improves d eeper into the travel. Maximum

velocity o n most landings from jumps occurs at YJ to \12

travel-this is w hen the po tential fo r cavitation is a t its

highest. This m ay be a design limitatio n but remember, all you need is enough pressure to eliminate cavitatio n and

no more.

O ther designs o f pressurized cartridges include W P units

o n some KTMs, which use a bladder w ith nitrogen instead

of a pressu re spring. (See Figure 3 .32 .) The pressure in this

d esign builds with the displacement o f the d amping rod and

the compress ion ra tio of the volume o f the reservoir chamber

compared to that o f the damping rod. T his makes it possib le

fo r the pressure to remain much mo re constant compared to

using a pressu re spring, thus the resistance to cavitatio n is

more consistent th rough the entire stro ke.

Other advantages o f pressurized cartridges include the

ability to use different viscosities in the inner cartridge and the

o u ter chamber. Increasing the viscosity in the outer chamber

makes the hydraulic bo nom -out mo re aggressive, if that's what

you need. This can be d one instead of replacing the bottom-out

"lock" ring with a larger diameter aftermarket ring, eliminating

the problem of scoring that these afrermarket rings often have.

There is also a mino r ad vantage with the separation of

the inner and o uter chamber o il in the event that the outer

chamber oi l gets contaminated.

There is, o f course, a downside to all pressurized fo rks:

added com plexity, additional sealing surfaces that increase

frictio n, and the number of places t hat there can be leaks.

Spring replacement is a bi t more involved as well. Remember,

too, that if there isn't any cavitation, the major advantage of a pressurized cartridge is minimized. Also no te that cavitatio n is

a much bigger issue on dirt bike fo rks than it is with street and road race forks because of the high ve locities involved.

Remember that the pressure spring in the reservoir does no r create damping- rather, ir creates pressure to eliminate cavitation and ultimately adds to the main fo rk spring force slightly. The pressure springs are position sensi tive, not velocity sensitive.

Supercross generates higher shaft velocities and more bottoming problems. To deal with it, tuners qu ite often opt for more mid-valve compression dam ping. These harsh cond itions require stiffer pressure springs in the reservoir, but which ones? The problem in answering that q uestion is that it's hard fo r the rider to detect cavitation . Typically the rider may feel it bottom or perhaps feel a looseness due to the decrease in rebou nd damping, but in resting, those symptoms are really hard to pin on cavitatio n. Most shock dynos cannot even come close to creating che velocities required to induce cavitation, so they won't be able to detect it either. T he ru le of thumb is: higher compression velocities and more mid-valve damping requi re stiffer pressure springs or more reservoir pressure. (See www.racecech.com for recommendations.)

OTHER FORK DESIGNS T he 2009 model year saw many new cartridge styles in troduced into the sportbike market. Suzuki and Kawasaki in troduced che BPF "Big Piston" forks with 39 and 37mm

pistons, while Yamaha brought our 30mm cartridges with com pression only in one leg and rebound only in the other.

If the notion of an " imbalance" created with compression

in one leg and rebound in the other seems to pose a problem , you can stop worrying-unless the front ax le flexes app reciab ly, both fo rk legs are going up and down ar rhe same time. In fact, in the 1980s Marzocch i had a series of dirt bike

forks rhac had only one fo rk spring: rebound damping was in that leg and com pression was in the o ther leg. T hough they were never considered the best-performing fo rks, the bikes they were fitted to showed no evidence of turning left better than right (or vice versa), nor did they exhib it any

unusual binding. T hese new designs have shifted from rod displacement to

piston displacement. Th is means that, instead of the damping rod volume displacing the fluid ro create compression damping, they are more like a shock where the entire vo lume

swept by che piston (cartridge inner diameter rimes travel used) is being used to make damping. In theory this provides the same advantage as the mid-valve does in dealing with the "compressibili ty" of the oil and expandabili ty of the

cartridge cube. T he downside, in my opinion, is char che damping

pistons are way too restrictive. The volume of oi l going through che piston on a 39mm BPF Showa is cen and a half times char which a 12mm diameter damping rod pushes in a conventional cartridge. T his means there is a big tendency for the pisto n o rifices themselves to create significant harshness.

But, to be fa ir, everything has upsides and downsides. The most im portant consideration is whether or nor a tuner can make che forks perfo rm, and rhe answer to that question is usually yes. T he degree of performance yo u can wring our of these designs depends on knowledge of rhe problem and ski ll in resti ng and troubleshooting o n rhe part of bo th rhe test rider and the tuner. T his is why Gold Valve Kies fo r these fo rks have radically increased flow areas.

SHOCK DESIGN le may come as a surprise, but rhe study of shock absorber design won't be pa rticularly difficu lt by chis point in che book. If you understand the previous concepts presenced, shocks are easy. T here are six major shock designs we are going to look at, scarring wich rwin- tube shocks.

Twin-Tube Shocks This type of shock is the most popular style on the p lanet by a long shot (see Figure 3.33). If yo u look closely, you can see ir looks very similar co a standard cartridge fo rk, with che shock shaft che equivalent of che damping rod . On che end of rhe shock shaft is a rebound piston wi th a check valve o n the top side. T here is a "base valve" (com pression valve) ac che bo tto m of che cartridge wich a check valve on the top side. Outside the cartridge is a compressible air space to deal wich the displacemen t of che shock shaft. T hese shocks must be

mounted in the orientation shown and cannot be inverted. There are subtle variations, like the addition of a Freon

bag inside the outer chamber instead o f letting the air contact the oi l directly. Contrary to what you might think, the use of Freon as a gas has nothing to do with cooling the shock. T his variation had limited improvement.

There are also designs chat feature a floating piston ring that seals on the outer d iameter of the ca rtridge tube and the inner d iameter of the shock body, allowing che shock to be pressurized through an opening in the seal head. T his is done in an effort to control cavitation and allows the shock co be

mounted in any direction.

Emulsion Shocks Emulsion shocks are single-tube shocks that have no reservoir

and are not quire fu ll of oil because they require an air space to deal wich che displacement of the shock shaft. T hey must be mounted in the orientation shown, with the body up and the shock shaft down. T he compression valving stack is o n the bottom of che pisto n while che rebound stack is on the o ther side.

These shocks are genera lly pressurized to raise the tempera cure and lower the pressure ac which cavicacion occurs wi th in che suspension fluid itself. As you might imagine, the potential for cavicacion and foaming is real-the idea behind the design is that o nce it "foams up," ic will become consistent. Emu lsion shocks can actually work qu ire well but are not co nsidered to be a high-performa nce design.

61

Twin-Tube 3.33 (Above) The twin-tube design looks very similar to a standard cartridge fork. The shock shaft has a rebound piston attached. The bottom of the cart has a compression base valve and there is an air space on the outside of the damping lube.

3.34 (Top right) This illustration shows the effect of shock shaft displacement. The solid shock shaft displaces oil volume in the shock body as it compresses. Because oil is incompressible, there must be a compressible space inside the shock for the entire stroke or ~ will not compress.

3.35 (Bottom right) All of these designs are related lo the original DeCarbon mono-tube design and are considered lo be high performance.

62

nitrogen (gas)

oil (liquid)

DeCarbon Internal

Floating Piston

shock shaft displaces volume inside body

Remote Piston Reservoir

Emulsion

nitrogen compresses r--;=;::::~-..r"

Integral Bladder Reservoir

DeCarbon Reservoir Shocks If we were ro separate the o il from the ni trogen with a floating pisro n in the main shock body, we would have a basic DeCarbon reservoi r shock. I group remote reservoirs,

bladders, and diaphragm reservoirs in ro this group. All are high-performance designs.

When the French scientist Dr. Christian Bourcier DeCarbon invented this design, he used a floating reservo ir

piston in the main shock body, but all the styles mentioned are variations of this rheme. Externally DeCarbon's original design looks like an emulsion shock, but internally it's quite d ifferent.

By pressu rizing rhe nitrogen space, we can reduce o r eliminate cavi tation. Remember that the amoun t of nitrogen pressure required is directly related ro the amount o f compression damping required-this was discussed in the pressurized fork sectio n. N itrogen is used in rhis design because ir's dry, inexpensive, inert, and easily acquired in high­pressu re borrles, bur iris nor rhe only gas rhar can be used.

One of rhe problems wirh rhe original DeCarbo n design for many mororcycle applications was rhar, because rhe floating pisron was in rhe main shock rube, rhe shock was considerably longer rhan a twin-rube or emulsion shoc k. A solution ro rhis was attaching a remote reservoir wirh a hose. Now this idea has evolved inro an integral reservoi r bu ilt inro the body. The integral design nor only sim plified rhe

design, bur it has rhe added benefit of a very short hear path to rhe added su rface area of the reservoir body keepi ng the oil cooler. Thar being said , if the shock doesn't fade appreciably with tempera ture (the shock loses damping when it gets hot), this adva ntage is unimportant.

Shock Adjusters Rebou nd adjusters can be used in a ll rhe shock designs mentioned. The adjusters generally posi tion a tapered needle in an o rifice and are low-speed adjusters. T here are two mechanisms fo r moving the adjuster needle. The first type uses a knob threaded onro rhe eyelet that moves a crosspin resting against the adj usting needle rod. The second type uses a sc rew with a tapered rip rhar pushes rhe rod directly. (See Figure 3.37 fo r details.)

Ano ther rebound ad juste r design has four posirions­th is type has a barrel inside the shock shaft with fou r different size holes in it. One of these holes is a ligned with an ou tlet po rt ro determine which one flows.

W hen rhe reservo ir is a ttached outside the main shock rube, we have the oppo rtunity ro add external compression adj usters. T he vo lume rhar rhe shock shaft d isplaces flows in to the reservoir and-while this may no t be a lo t of fluid­is enough ro influence the shock's behavio r with an adj uste r.

Increasing the shaft diameter increases the vo lume of flow ro the rese rvoir, making the adjuster more effective.

T here are many adjuster des igns: a simple one is shown in Figure 3.37. T he low-speed adj uster is the o ne on the right

and is just a simple tapered needle in an o ri fice. T he high speed adjuster on the left is a coil spring on a valve plate: using rhe adjuster airers rhe spring preload . On rebou nd the refill check valve opens and allows rhe oil ro return ro rhe mai n shock body.

Most production compression adjusters are fa irly ineffective, so much so rhar when doing blind resti ng, most riders cannot rel! much d ifference with any of the settings. T hese findings have been backed up wirh dyno resting. The advantage of ineffective adjusters is that the user can't mess it up-on the o ther hand, they can't improve things much either.

There are no general sta tements rhar can be made about which brands of adjusters are more effective, bur this is where good testing o r dyno work comes in . O ne of rhe design considerations of Race Tech G3-S Cusrom Series Shocks was ro have a significant range of ex ternal compression adjustment. We were ab le ro achieve an impressive range of 33 percent.

Through-Shaft Shocks A simple version of a through-shaft design is a linear steering damper, with compressio n valving o n one side of the piston and rebound on the other. The shock is com pletely filled with o il. Generally speaking, rhere is no compressible air space required because the shock shaft volume going in is equal to the volume going our. H owever, it is preferable ro have

a compressib le space ro allow for expa nsion of the oil with temperature. T his basic design is used in Race Tech Caddies Softail Shocks.

Solid-Piston Shocks Solid-piston shocks can be linear o r rotary vane style. The linear version shown uses a so lid piston in a twin-rube design.

Passages or hoses are attached to the inner and ou ter rube and a valving block can be bu ilt into the shock body o r attached with hoses and remotely moun ted. This basic design is used by Ohlins in its TTX Series shocks (see Figu re 3.39).

This Scott's Steering Damper is a rotary vane damper that does an excellent job of controlling headshake. Even ff headshake is not a problem, the damper allows the rider to relax qutte a btt more.

63

top mounting eye

shock body

threaded preload adjuster

piston

shaft

seal head

bottom-out bumper

low-speed rebound adjuster

rebound base plate

spacer

piston

low-speed rebound damping adjuster seat

low-speed rebound adjuster inlet port

shock shaft

3.36 Shock Valving Components

T he TL! OOOS Suzuki introduced in 1997 uses a ro tary

va ne style damper attached to the swingarm with links and

heim jo in ts. T he spring is attached separately o n a unit that looks li ke a shock but isn't. The valving consists of two

assemblies that look very much like cartridge fo rk valves, with

64

compression adjuster

reservoir oil passage

reservoir

bladder

nitrogen

snap ring

reservoir cap

nitrogen filler

lower spring perch

bottom mounting eye

shaft nut

---- high-speed rebound shim stack

low-speed rebound shim stack

low-speed compression shim stack

high-speed compression shim stack

L...--.....:::::~~:!--- compression base plate

r="'=lr------- low-speed rebound damping adjuster needle

one controlling compressio n and the o ther rebound- in fact, we fit Fork Gold Valve Kits to these when we reva lve them .

T he TL dampers suffer from high friction and a tendency for

the attachment heim joints to get sloppy, but they can be made to

work very well with internal polishing, anodizing, and care of the

Rebound Adjusters

cross pin

adjusting knob

3.37 Shown are the two most common types of rebound adjusters where a rod through the center of the shaft positions a tapered needle into a seat. It is being moved by either a threaded adjusting collar or an adjuster

screw with a point on the end. The high- and low-speed compression adjuster shown is one of many types available. Most of these designs use the flow from the shock body to the reservoir to create additional compression damping. The tapered needle adjusts low speed while the preload on a coil spring pushing onto a piston controls high speed.

if there is only one clicker, it is usually low-speed

Compression Adjusters

clicker adjusts sp ring preload

heim joints. T heir big downfall was a lack o f underscanding by

tuners, who removed the stock damper and easily (and perhaps too

eagerly) replaced rhe spring unit with a complete standard shock.

Ir is notable because it was, as fa r as I know, the fi rst production

version of a solid-piston shock design.

clicker adjusts orifice size

Another version of rhe rotary vane design is a Scott's Steering

Damper. These are nor suspensio n units technically, but they do

dramatically affect handling , and they are a damper. There are

pavement and dirt versions, and they have bo th h igh- and low­

speed damping adjustment and perform very well.

65

Through-Shaft

3.38 Through-shaft shocks don't require a reservoir as the shaft volume entering is the same that is leaving. Reservoirs are only added to compensate for the expansion of the fluid with temperature.

POSITION-SENSITIVE DAMPING SYSTEMS In the Race Tech Technical Edge Suspension Seminars, we delve into linkages and leverage ratios in quite a bit of detai l. Linkages (and, in fac r, all shock mountings) have a leverage ratio curve. The leverage ratio, as we defi ne it, is basica lly the t ravel of the wheel divided by the travel of che shock. W ith a

linkage, the opportunity co vary che leverage ratio through the stroke becomes quite significant.

T his allows the suspension to be plush on the li ttle bumps and stiff on the big ones. T his is, obviously, of particular

significance for dirt bikes. W ithout a linkage, the abili ty to change the leverage throughout the travel becomes quite limi ted. Through testing on dirt vehicles of any type, we've

found that a progressio n of25 to 32 percent is a good range of change berween 50 and 250mm travel.

W ithout a linkage, it is d ifficu lt co gee more than about 12 percent. T his means setups without linkages-including ATVs and automotive A-arms-benefit not only from progressive spri ng setups but also position-sensitive damping.

You might recall that l said damping is sensitive to velocity, not position. T his is precisely true. It is, however, possible to make the damping change th roughout the position of the stroke as well.

66

Solid-Piston, External Valving Block

3.39 Solid-piston shocks come in many forms. In this case the oil is pushed through a valving block to create damping. The reservoir is attached between the valving pistons where the pressure is lowest. This allows a lower required pressure.

There are a number of ways co do this. O hlins uses rwo d ifferent size pistons attached to the shock shaft with the piston on che end o f che shaft going in co a "cup" in the bottom of the shock body at the end of the shock stroke. ln the au tomotive off-road world, King Shocks have external bypass cubes located at diffe rent heights along the shock body. The WP PDS (Position Sensitive Damping System) also uses two pistons similar to O hlins, but both pistons are the same size. W P's design is by far the most popu lar in the motorcycle world , particularly because they come as original equipment on KTM mo to rcycles. KTM removed th e shock linkage and mounted the shock directly from the swingarm co the frame in 1998. This introduced the need to make both che spring rate and the damping change with position.

Referring co Figure 3.40, you can see there is also a metering needle attached to the bottom of the shock body. There are two phases: the fi rst is befo re the needle enters the shock shaft, and the second is after the needle has entered. ln the ini tial movements befo re the needle enters, the o il

oil

A

nitrogen

B

flow goes from chamber A th rough the cencer o f che shafc,

bypasses che "seconda ry" piscon, goes ou c chrough pores in

che shafc and spacing sleeve, and goes ch rough the "p rimary"

pisco n compressio n circuics.

Once rhe shock compresses enough co engage che

m ecer ing needle, che o il in chamber A can no lo nger

bypass che secondary piscon, so ic is forced ch rough ic.

T he damping creaced by che secondary piscon is added co

che damping creaced by che primary piscon because che same

volume o f o il still flows ch rough che prima ry piscon.

3.40 The first phase of a PDS Shock is before the shock has collapsed enough to engage the pin. The oil can flow to the primary piston through the center of the shaft, bypassing the secondary piston. The problem, historically, is the center of the shaft has too much restriction.

PDS needle

oil flow bypasses secondary piston

From my perspeccive, che majo r flaw in chis syscem is

che rescric cion in flow area co che p ri mary piscon chrough

che center of che shafc. I did a series of cescs with che PDS

in 1999 and initia lly, no maccer what I d id with the valving

on the primary piston , ic was always harsh o n square-edged

bumps. Then I removed che secondary p isto n en tirely.

The rider's feedback was chat it was much plusher on braking,

acceleracion, and small, single, square-edged bumps. The

scandard metering needle was no r engaged in chis area! All

char needed co be tested then was to put che secondary p isco n

67

back on and remove the metering needle enti rely- it was ha rsh again. O ver the yea rs WP has increased the bore size in the center of the shaft, and this has helped.

Terry H ay of Shock Treatment (Race Tech's Australian distributor) invented a novel solution that has had worldwide success. One of the problems with the stock metering needle was it was very short and , if it were any longer, the needle would hi t the rebound seat and start des troying thi ngs.

Terry made a metering needle that was much longer than stock and telesco ped in to itself. T his made rhe

oil

nitrogen

B

68

progress io n mo re consistent. Bu r what abou t rhe res triction in flow ra re? H e simply su rrendered ro rhe fact rhar rhe bore of the shaft wou Id be restri ctive and fo rced rhe secondary piston ro flow o n high speed hits througho ut rhe enti re st roke. This required a significant decrease in compressio n damping o n rhe secondary pis ton. In my opinio n (and yes, I a m biased), Terry's Telescopic PDS N eedle alo ng wi rh Race Tech's P Series Progressive Shoc k Springs and a G old Va lve combine to significantly improve the KTM suspension performance.

3.41 Once the pin is engaged, all the oil is forced through the secondary piston on ~sway through the primary piston. The damping created by both pistons is added together. This abruptly increases the damping toward the bottom of the stroke.

POS needle blocks damping rod shaft, forcing oil through secondary piston, creating additional damping

primary piston continues to create damping

rebound adjuster flows slightly

oil

the solution is a telescoping PDS needle

standard PDS needle has a short taper, and is harsh

lengthening the PDS needle taper can cause the needle

inlet port for high­pressure oil, which extends the needle

passageway for low-speed circuit

to strike the low-speed orifice

the telescoping PDS needle collapses when it contacts the low-speed seat

I I

nitrogen

the telescopic needle has a long gradual taper for smooth damping progression

3.42 The Telescopic Needle creates a gradual progression over a longer stroke eliminating the abruptness and harshness. This is enhanced with revalving.

69

<!I z ii: ::!: ci: c

FADE Fade is a decrease in damping duri ng use. Ir is usually caused by one of three things. First is the loss of viscosiry when rhe o il hears up. (Losing viscosiry means char rhe oi l chins our.) T his can be because rhe viscosiry index of rhe oi l is low (poor qualiryoil) or because rhe o il's viscosiry index has broken down with wear (poor qualiry viscosiry-index- improver addi tives) . T his decreases damping, parricularly in rhe low-speed range. Remember char, o n rhe energy level, a shock converrs kinetic energy inro hear, so rhe shock hears up when in use. Fronr forks generally hear up much less than rear shocks because there are rwo fork legs instead of o ne shock, giving rhe fronr forks much more surface area in comparison ro rhe shock. T hey are also up front hanging ou r in rhe breeze cooling off, while the shock is ofren stuffed in and hidden from the wind. On some models the shock is exrremely close to the exhaust pipe, wh ich doesn't help marcers eicher. Fade can also be caused by che o il becoming more compressible as ic hears up.

Another cause of fade is mechanical blowby. T his can happen when d ifferen t materials expand differencly as they heat up. If che shock body is made of aluminum and che pisron is made of steel, che aluminum body expands faste r than the steel pisron as che shock hears up.

T his is nor a problem if che sealing design o n the pisron can hand le thedifference in expansion.A poorseali ngdesign, however,

Cl)

c.:I ... Cl u.. en c =-E ~ c c Cl en en Cl) ... =-E Cl u

can leak. If the oil is going around the pisto n and not through it, the damping decreases and the rider experiences fade.

A common culprit is the energizer 0-ring underneath the piston band . O n KYB and Showa shocks, par ticularly on o lder models (pre-2000), the energizer 0-ring can wear off and form a flat spot, lessening the preload on the piston band-sometimes to no thing. T his problem is hidden because the stock piston band is endless (full-circle hoop) and doesn't expose the conditio n of the 0-ring. Measure the installed outer diameter of the piston band and make sure it is larger than the inner d iameter of the bo re.

Ano ther source of fade is cavitation, an issue we have

d iscussed in quite a bit of detail already. If the shock loses pressu re for any reason, it will show up as a dec rease in damping bo th on compression and rebound.

I remember when a rider came up to me and cold me he had f1Xed the harshness problem on his stock shock. He co ld me he let some of the nitrogen pressure out and now it's great. I asked him how much, and he cold me he only lecouta lin le-he just pressed the valve core and it wenr "pssssssst." T hat might be almost all of the pressure, for all I know. N ow, I wanr to be clear, I'm not

suggesting chat chis is a solu tion fo r harshness. I'm presenting it to describe the effect of cavitation. Any time the compressibility of the oil increases, as with cavitation, the damping decreases. To be clear: chis was not a viable solution to the harshness problem.

Velocity 3.43 Damping curves come in many shapes and styles. The orifice curve is of the classic velocity squared variety. Tapered or straight stacks provide a linear curve. Two-stage stacks increase the rate of change in damping when the low-speed shims touch the high-speed stack. Preloaded stacks are digressive. Freeloaded stacks start open therefore begin quite similar to orifice, however as the velocity increases, the shims bend, and the damping is less than it would be ~the orifice were fixed.

70

VALVING STYLES We are go ing ro look at a number of valving sty les as seen in Figure 3.43. T he major q uestion is: how progressive do you wane it? T he shore answer-progressive enough but not roo progressive. Perhaps not the answer you wanted to hear, but this is what we do when we go testing. We are re-shaping the damping curve. More progressive is not necessari ly better no r is being roo li near o r digressive. The trick is ro fi nd the right shape curve for the specific application. Keep in mind that damping is sensi tive ro velociry, so the shape of the bump is as big a deal as the size. Small square-edge bumps can cause

single-stage flat piston no preload tapered stack

clamping shim

3.44 This is a very common valving style for road race and street bikes.

Q) (,) ... = LL.

= = =-E ~ c = =

damping curves are additive: A+B = C

/

quite high velocities, and rounded bumps hit at very high vehicle speeds can do the same.

Orifice Style Valving We've looked at orifice-sryle damping and its d rawbacks. The fact that it is related to the shaft velociry squared means that when the velociry is doubled, the damping increases by four. The result is a suspension setup that feels both mushy and harsh.As we d iscussed before, both the Emulator and cartridge fo rks were invented to eliminate this rype of damping.

Single-Stage Valving Referring to Figure 3.44 the first rype ofbendingshim sryle valving stack we'll look at is a single-stage, Aat piston, and no preload, tapered stack. Most modern valving systems use some kind of bending shim valving stack on a valve piston . T his rype of valving is inherently linear, meaning that if you double the velociry, the force increases by a consistent percentage. By changing the stiffness of the valving stack, the rate of increase is tuned.

It may seem confusing at fi rst glance but notice that these illustrations only show the left half of the stack and don't show anything on the top side of the piston .

Additive Damping Imagine fo r a moment that we remove the shim stack from the piston entirely and decrease the feed port size. W hat do

I r combined I j dam~~/)~ I "" vv I

7 )v ~ ~ / ~~

.......

"' "' Q) ... / v~ ~ ~ ~

l shim-style r / linear damping

=-E = (..)

~~

/_ ~

/, ~~ / " __ .--~ ~

v _. v ~\_~

~ orifice-style

/ ~ progressive ,,...,.,.., damping

~

""=::>

Velocity 3.45 This shows how damping is additive for a typical piston and valving stack. In this case, curve A is created by the piston orifi ces alone and is proportional to the velocity squared. Curve B is the linear damping created by the single stage shim stack alone. Curve C is the total of both the piston and the shim stack combined.

71

we have? We have orifice-style damping. We've just turned a cart ridge fo rk into a damping rod fo rk. T he po int here is that just because it is a cartridge doesn't mean the valving works well. T here are, in fac t, models that have come fro m the factory with this scenario.

Next, let's replace the sh im stack. As mentioned, shim stacks are inherently linear, so if we install a shim stack on this res tricted , small-port piston, the damp ing of the shim stack is added to the damping of the piston. See Figure 3.45 .

To figure out if a change to a dam ping system adds to o r decreases from the existing damping, the key question to answer is, "Does the same amount of o il flow through that circu it?"

Let's say we added a compression adjuster to a shock and it fu nctio ns on the volume of oil that goes into the reservoir­in th is case it doesn't affect the volume of oil going through the compression va lving. T he compression adjuster therefore adds to the overall da mping. T he add ition of a mid-valve on a fork doesn't change the volume of oil going through the fork com pression base valve and , once again, is additive.

On the other hand, on a carcridge fork, the low-speed compression adjuster bleed circu it is separate from the main compression piston shim stack. Backing out the adjuster and increasing the bleed size increases the flow through this adj uster circui t. T he increase in flow th rough the adjuster circuit comes at the expense of the flow th rough the main piston shim stack

circuit, meaning that rhe overall dam ping is decreased.

Gold Valves We introduced the digressive concept when we introduced Emulators. H ow does this concept apply to cartridge fo rks o r shocks? W hen the piston po rts are overly restrictive (too

small) the damping created by the piston alone may a lready be too harsh on high-speed hi ts. To make matters worse, the

shim stack adds more damping on top of rhar. This may work o k at low speeds, bu t on high-speed hits it's way too stiff.

I invented Gold Valves in the very ea rly 1990s and, at the time of this publishing, we have over 60 unique valve designs

with many different port configu rations. In general Gold Valves increase the flow area. T his increase has a very similar

effect to that found in damping rod fo rks when we drill ou t the stock compressio n damping holes when insta lling an Emulator. The compression ho les on the damping rod serve the same function as the compression dam ping piston ports. Gold Valves put the damping contro l onto the shim stack, a llowing a much greater range of tu ning flexib ility, including the ability to dramatically reduce harshness.

72

Two-Stage Valving We have already looked at two-stage valving in the cartridge fork section. Two-stage valving (Figure 3.46) is common ly

used in dirt bikes where a large range of demands are placed on the suspension. One thing that makes d irt bikes more cha llenging is that they commonly encounter bumps much greater in size than their suspens io n travel. Landing off jumps can generate very high ve locities as well. D irt bike forks on a normal motocross track quite commonly see 7 m is velocity with an average rider. They also have to deal with "no rmal" lower-speed situations like brake dive go ing in to turns. Two-stage valving is a good setup to hand le this range of obstacles.

The smallest-d iameter shim-the o ne fa rthest away from the piston-is called the clamping shim. Its d iameter is the most critical pare of che valving stack because all che ocher "working" shims bend on it. On a two-stage stack chere is a small-diameter shim that separates che low-speed stack from the high-speed stack. This small-diameter shim is ca lled the crossover shim, and both its diameter and thickness are important. Using a larger diameter will stiffen up the low­speed wh ile a thicker c rossover wi ll delay the stiffening support of che high-speed stack, making it softer.

A good rule of thumb is chat che crossover d iameter should be larger than or equal to rhe diameter of the clam ping shim . This helps main tain the crossover gap.

O n dirt bike shock com pression sracks, ir is nor uncommon to use three-stage valving stacks. Note chat genera lly the more stages there are the more progressive the curve will be. The overall suspension stiffness, however, still depends on the stiffness of the specific stack. In other words, a three-stage stack could end up either stiffer or softer, or more or less progressive, than a two-stage stack, depending on the exact shim sizes. How many

low-speed stack

high-speed stack

two-stage flat piston no preload tapered high-speed stack

crossover shim )

clamping shim

3.46 This valving style is commonly seen in dirt bikes where the velocity range is much higher than for street bikes. Landing off jumps as well as rocks and roots can cause particularly high shaft veloc~ies.

stages work bes r is determined solely by resting. T har being said ,

d irr bikes generally use mo re srages rhan pavement bikes.

Preloaded Stacks T here are siruarions where additional low-speed dam ping

is desired bur wi tho ut the additio n o f mo re high-speed

damping. Supermom is an excellent applicatio n fo r this type

o f damping- it requ ires p irch co ntrol because o f irs lo ng

travel and heavy braking. This means controlling rhe fro nr-ro­

back movemen t experienced du ring braki ng and acceleration.

If, wi rh a no n-p reloaded stack, t he stiffness of the stack was

increased eno ugh ro control rhe pirch (a relative ly low-speed

phe no meno n), the ride over square-edged bumps would be

q uite harsh.

Refer ro Figure 3.47 ro see char preloading can be

accomplished a number o f ways. The first illustration shows

rhe use of a flar pisron with a " hoop shim." T h is is a large

inner-diameter shim. T he "nesting shim" is thinner and fits

inside rhe hoop shim . The difference in thickness o f rhe hoop

and nesting shims provide p reload fo r the resr of rhe working

shims. By varying the thickness of the nesting shim as well as

nesting shim

the sti ffness of the resr o f the working shims, the shape of the

damping curve can be conrrolled nicely.

Another method of preloading is "stepping" rhe face of

rhe piston to create a "recessed" piston. The step is like a packer

in rhe piston face. If the step is .2 mm deep and the shim stack

is bolted direcrly o n ro it, the preload will be .2mm .

Instead of stepping the face of the pisto n , a taper can be

machined as we ll. This will produce simi lar results as the rwo

previous methods.

Race Tech's G2-R Gold Valves provide a mo re ad vanced

version of preloading, thanks ro the add itio n of res rrictor

stacks . (See Figure 3 .48.) The G2-R star ts wirh a stepped

p isto n with large por ts, and rhen the restricror srack goes

against the piston face ro contro l preload . In fact, the preload

can be reduced to zero o r even "freeloaded."

T he res tricro r srack can also be cha nged in diam eter

to increm e nta lly restri c t the p isto n por r size. If you're

t hinking rhar I've been saying " b igger is better" through

rhe course o f thi s book, you're rig h t-bur there a re a lso

t imes w he n this isn' r the case. In supercross, fo r insta nce,

o ne of the key requ irements is bo tto m ing resis tance,

3.47 (l eft) Two methods lo create preload are shown. The first is through the use of a large inner-diameter "hoop" shim. The "nesting" shim rns into the hoop shim inner diameter and is thinner. The difference between the thicknesses is the preload. The second method steps the piston face itsett. A variation of this is an actual taper on the piston face.

single-stage flat piston hoop shim preload tapered stack

single-stage recessed piston preloaded tapered stack

3.48 (Below) The G2-R Valve is extremely flexible. It can be preloaded, freeloaded, restricted incrementally. This adds some complexity but offers the highest degree of tunability.

G2-R two-stage recessed piston preloaded very restricted port size tapered high speed stack

restrictor stack

restricted port

G2-R single-stage recessed piston zero preload restricted port size tapered high speed stack

unrestricted port

G2-R single-stage recessed piston freeload unrestricted port size tapered high speed stack

73

because supercross la ndi ngs are typ ica lly rhe h ighest veloci ties recorded in a ll of mororcycledo m . T he key poin t is, w hen shaping a dam p ing c urve yo u wan r ro c rea te rhe best p rogressio n , no r rhe mosr a nd nor rhe leasr. In gene ral I like ro use jusr e no ugh com pression damping and progression ro do rhe jo b (resis t bo rroming, con rro l di ve, a nd so o n) a nd no mo re.

Freeloaded Stacks A freeloaded srack is one rhar starts wirh a small-diameter shim against rhe piston face. T his shim does nor cover rhe feed ports in rhe piston and therefore presents an open orifice ro rhe oncoming flow. I r is rhe mosr progressive sryle of da mping outside of a fixed o rifice.

T his sryle of srack has been tried a number of times over rhe years (including by myself fo r qu ire an extensive period). In my experience, ir never works. Ir exhibi ts the same drawbacks as o ri flce-sryle damping, namely, ir's mushy and harsh . Ir also has rhe added challenge of sealing rhe pisron off o n rhe rebound stroke.

Straight versus Tapered Stacks O ne question rha r comes up commonly in rhe Race Tech Suspension Seminars is, "Why use a tapered srack instead of a srraighr one?" I r is a widely held belief rhat rhe tapered stack is more progressive rhan rhe srraighr one. T his is nor rrue in

the deflection (velocity) range these stacks actually see. T hey are bo th linear stacks, meani ng rhar once rhey open , rhey increase stiffness ar a consranr slope.

Many ru ners m istakenly add thicker o r more shims "deeper" in rhe srack in an arrempr to create a more progressive

high-speed response. T his a rrempr is furi le as rh is is nor how rhese stacks work: rhey are linear. Increasing rhe stiffness deeper into rhe srack or higher in rhe srack makes rhe enri re srack stiffer.

single bend axis is prone to permanent distortion

So why tapered stacks? Simple- this helps prevent rhe permane nt d istortio n of rhe shims (Figure 3.50). On a srraighr stack all rhe shims open rhe same amount and rhey all bend on rhe clam ping shim, so rhe srress is concenrrared ar rhe bending point. Wirh a tapered stack rhe working shims bend ar m ultiple poin ts (on each preceding shim), spreading our rhe stress. Tapered stacks also have more clearance to open before they hi r rhe base plare (thick washer).

Thin Shims versus Thick Shims H ave you ever wondered why shock manufacturers use large numbers of rhin shims aga inst rhe piston face instead of a smaller number of thicker shims? T here is more than one way to create rhe desired stiffness of a valving srack, afrer all. Sometimes fi fteen . 15mm thick shims are used instead of a lesser num ber of th icker shims-why?

No, ir's nor progressiveness, or rhar rhey had a bunch of extras lyi ng around . T he answer is permanent d istortion. If yo u srack up a rhin shim a nd a rhick one made our of identical materials, clamp them in a vise in rhe midd le and starr bending borh of rhem ar rhe same rime, you will no rice rhar the rhicker shim permanen dy distorts before the th inner one.

The reason is rhar as rhe shims are bending, rhe molecules on rhe rop are being srrerched while rhe ones on rhe bottom are being compressed (see Figure 3.51). In rhe m iddle is a "neutral axis" where there is no st ress. The further away from rhe

neutral axis, the more stress on the molecules. The molecules furthest from the neu tral axis are working the hardest. T his means chat a thicker shim , with molecules further away from the neutral ax is, will d istort with less deflection .

So where are the ch inner shims used ? Typica lly they are found in the low-speed stack of a rwo-stage stack. T hey are used in rhar conrexr because rhe shims in rhe low-speed stack have to bend further rhan rhe high-speed srack by the th ickness of the crossover.

multiple bend axes I resist permanent distortion

single-stage flat piston

single-stage flat piston

single-stage flat piston

gap shim "freeloaded" tapered stack

3.49 A "freeloaded stack" has clearance between the first working shim and the piston. I have never seen this work. It is similar to orifice style damping.

74

no preload straight stack

no preload tapered stack

3.50 Contrary to popular belief the tapered stack is not progressive. Its advantage is that it has multiple bending axes that assist in smoothing the abrupt bend of a straight stack thereby resisting permanent distortion (creasing). It also provides more clearance from the base plate.

tension

So the next q uestio n is how does the stiffness va ry with

t h ickness? The stiffness is proportio nal to the thickness

cubed , but keep in mind chis is o nly valid for shims of the same d iameter a nd material. Refer to the chart below

for guidance.

W hat this means is it takes eight . I Omm thick shims to

equal the sti ffness of o ne .20mm chick sh im. This can come

in qu ite handy when compari ng valvi ng stack stiffness, o r

if you find a valving stack with shims cha t a re permanen tly

distorted . If they are distorted and the rider liked it when it

was just revalved , yo u can calcu late ano ther stack wi th the

equ ivalent stiffness o f the o riginal stack but made out o f

chinner shims and , quite possib ly, eliminate the p ro blem.

Rebound Separator Valves O ne of the problems wirh a standard low-speed rebound

adj uster is chat it flows in both directio ns. W hen it is sec

perfeccly fo r rebound , iccan be way coo mushy o n compressio n

and , in certain conditio ns, bo ttom easily. W hen it is nice

Shim Stiffness to Thickness Coefficient for a fixed OD

t t3

0.10 0.001

0.15 0.0034 11 - Stiffness Coefficient

0.20 0.008 oc - is proportional to

0.25 0.0156 t - Thickness of Shim

0.30 0.027

II

1

3.4

8

15.6

27

3.51 When a beam attached to a wall is loaded, it bends. The material on the top surface are being stretched apart while the material on the bottom is being compressed. There is an axis right in the middle that has no stress at all called the neutral axis. The further away the material is from the neutral axis, the more it is stressed.

and firm o n compressio n , it is way too slow o n rebo und,

causing packing and loss of tractio n. The solutio n is to create

asymmetric (different in each directio n) damping. This can be do ne in many ways. I first observed it o n '8 1

Ho nda CR250s and 480s with Showa shocks. Showa changed

the location o f the asymmetric va lve to the inside of the shock

shaft shor tly thereafter. O hlins has had a valve attached to the

end of their shock shafts for a number o f yea rs as well.

In 2004, Terry Hay (yes, the same Aussie with the PDS

Telescopic Needle) created a versio n of chis concept chat could

be incorpo rated o n a stock shock. H e ca lled it a Rebound

Separato r Va lve (RSV) . le was built in to a replacement shock

shaft nut. See Figure 3.52 .

Here's how it works. Starting o n the rebound stroke

there is a check valve that o pens up causing the rebound

to fu nctio n normally, wi th the tapered adjuster need le

co ntrolling the flo w. O n com pressio n the check valve shuts

and the ad justable rebo und circu it is fed with a b leed ho le

specifically sized for the applicatio n thereby giving it mo re

low-speed com pressio n damping. The m odificatio n improves

tractio n and feel as well as bottoming resistance. Race Tech

has utilized Rebo und Separator Valves with im pressive

feedback in all genres.

Other Valving Styles There are a number of o ther styles of valving systems. Am o ng

these are ball bearings covering piston ports chat are p reloaded

by coil springs. T hese springs can be varied in both rate and

length to create the desired damping cu rve. T h is system has

been employed by Works Performance Shocks fo r years with

great commercial success.

E mulators use coil springs preloading a valve piston. As

mentioned previo usly, the valve spring stiffness, preload , and

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the ugly truth comes out: for simplicity, we have ignored that oil flows BOTH WAYS through low-speed orifices on compression and rebound strokes

the solution is the rebound separator valve that creates asymmetric fl ow in the rebound ci rcuit

check valve open, flows freely on rebound stroke

check valve closed on compression stroke

shock shaft

Compression Rebound 3.52 The Rebound Separator Valve solves the problem of an open bleed that flows in both directions. The RSV creates asymmetric flow using a check valve.

bleed size can be changed ro con tro l che shape o f che dam ping

curve q u ite nicely.

T he re are leaf spring syscems and even sys tems chacchange

che o il viscosiry wich a magnetic field. T here are also systems

chat use o n ly electro-magnetism and no fluid. T hese have

po ten tial fo r regenerative features by captu ring che energy and

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recharging batteries. These last two methods seem promising

as we move fo rward into p rogram mable valving systems.

The lesson here is chat I don't care how yo u create che

damping cu rve; all I ca re about is what che cu rve is . If ball

bearings a nd coil springs wo rk, chen chey work. T here are

many, many ways to create a da mping curve.

Chapter 4 Friction F riccion is che resiscance char one objecc encouncers when

sliding over ano cher. The amounc offriccion is dependenc

o n rhe macerials char are in concacc wich each ocher, che

no rmal force, and whecher chere is movemenc or nor. Friccion

cums kinecic energy inco hear. Ic is my opinion char friction is che firsc area char should

be addressed before any ocher suspension cu ning o r secup is do ne. Measure scacic sag and che "sciccion zone" co gee clues as

co che severicy of che problem and work co minimize friccio n

before moving on co springs and damping.

T he main chi ng co remember abouc friccion is: " friccio n ... bad" .

STATIC FRICTION Sciccion, o r scacic friccion, refers co rhe friccion presenc when

rhere is no movemenc becween che surfaces. Sraric friccion is

dependenc on cwo ch ings. The firsc facco r is che coefficienc of friccion µ, which is dependenc on macerials, cemperacure,

surface finish , and so on. T he seco nd faccor is che force

perpendicular co che surfaces ac che concacc poinc, referred

co as che "normal force" [F"0,m) . The fo rmula is Ffr;co;on =

µ X F nornul"

You may have reacced co che face char che surface area

in concacc is no r in che fo rm ula. In mosc cases friccion is

complecely independenc of surface area. There are excepcions

co ch is; mosc significanc is rubber on che road , possibly because

che macerial squishes in co surface irregularicies.

There is a lmosc always a layer o f "scuff" becween che cwo

surfaces, and ic has a big effecc on friccion. The scuff can be

composed of many chings: oi l, grease, mo iscure, oxides, ere. If there's a chin layer o f grease on che surfaces, it can cut friccion

tenfold in comparison co completely clean . If the scuff is

4.1 Surface roughness has an effect on friction but not as much as you might think. It is believed that this has something to do w~h the number of contact points even on a "smooth" surface.

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completely removed, friction forces can be huge, and the two

surfaces can seize together completely.

Just to be clear, the frictional force does no t exist until

the side load is applied. The more the side load , the greater

the friction, until the maximum frictional force has been

exceeded and you get movement.

If we have a block sitting o n a horizontal surface, the

weigh t is pushing down vertically. In this case the normal

force is equal to the weight. If we apply a side load parallel to

the surface [F,;d), this load will cause the block to move if it is

greater than the maximum avai lable frictional force.

No movemenc if: F sidc < F rrictionmu

Movemenc if: F sidc > Ffric1ion nl:lx

W ith this d rawing we introduce the co ncept of vectors.

T he vectors are the arrows representing the fo rces. Vectors

have both magnitude and direction- the size of the force

(magnitude) is represented by the length of the arrow (doub le

the force = do uble the length o f the arrow).

addition of vectors

vecto r B

vector A

A+B=C

4.2 In this example the block is resting statically on a horizontal surface. The normal force is equal lo the weight of the block. When a side load is applied there is an equal frictional resisting force created. As the side load is increased so does the frictional force up lo a maximum value of the coefficient of friction limes the normal force. Al this value ii breaks loose and goes into dynamic friction, which is typically slightly less than the maximum static value.

One of the great things about vectors is that we can add

them together o r break them apart. T h is allows us to solve

complicated things easily. The rule is that if we have two

vectors and we want to see what their combined effect is, we

simply place the tail of the second vector o n the tip o f the first

vector. T he combined effect of both vecto rs is represented by

a new vector starting at the tail of the first vector and end ing

at the tip o f the second. This is called the resultant vector.

This technique can be done with any number of vectors

added to each other. It is often used for breaking forces apart

into perpendicular components, as we will do in a moment.

Now, let's go back to our example . If the b lock is on a n

incline (see Figure 4.4) and we have no o ther external forces,

the normal fo rce is not equal to the weight. The no rmal

fo rce is the component o f force pushing perpendicu lar to the

surface . In the graphic you can see the weight is still vertical,

but we have broken it up into two parts and replaced it with

two fo rces. The first is the component pushing the block

down the hill (F down •h< hH1), and the second is the component

pushing it into the hill (F p«pcnJ;culu •o •hc h;ll).

breaking vectors apart

C=A+B 4.3 R>rces can be represented by vectors that have both magnitude and direction. Vectors can be added together or broken apart into any direction that would help our analysis.

78

F weight perpendicular to hill

F hiclion = µ X F norm al

T he no rmal fo rce is equal to the component of the force

pushi ng it into the hill (note that it is less than the weight). The

same calculatio ns regarding movement still apply. In this case

the side load that could cause movement is the component o f

the weight parallel to the surface (F wdgh• down•hch ill) .

Fork Dynamics Ler's look at what happens in a telescopic front fork w hen the

wheel hits a bump. Upon contact, the fo rce is directed radially

from the point o f comact to the ax le. (See Figure 4.5.)

We can now break this force into two compo nem s: o ne

that compresses the fo rk and o ne that tries to bend it in ha lf.

T he compo nent tha t tri es to bend it in ha lf increases the

no rmal force o n the fo rk bushings and therefore increases

friction that inhibits move ment. The comact actually

does bend the tubes, particu larly whe re it has the most

leverage-right below the triple clamp. Keep in mind that

this bending is tempo ra ry, as t he tube sp rings back when the

load is removed . W ith upside-down forks, th is means the

inner (upper) bush ing must go th rough a kink jus t below

the triple clamp. T his can cause severe binding and excessive wear on the inside of the o uter tube .

On severe hits, particularly o n dirt bikes, the fric tio nal

force can be greater than the damping and the sp ring fo rces

combined . If you are testing to eliminate a harsh fo rk actio n ,

look at frictio n first. Pay particular arrenrio n to the sliding

surface o n the inside o f the o uter fo rk tu be. If the hard

a nodizi ng is wo rn through , this may be the source o f your harshness. If you do n't take care of it, yo u' ll never get the

performance you are looking fo r. We' ll explain mo re o n hard

anodizi ng in a mo ment.

FORK SLIDING BUSHINGS In the beginning fo rk sliders were made of aluminum

a nd contacted the hard-chromed fo rk tubes directly. This

4.4 When the block rests on a hill, the nonnal force decreases. The weight of the block creates a force tending to push the block down the hill. The value of the forces can be calculated by "breaking the force into components• using the concept of vectors. The steeper the slope, the more the downward force and the less the nonnal force. Additionally this decrease in nonnal force lowers the friction available to resist movement.

configuration didn't wear well no r was it very slippery. Next

bronze bushings were introduced , and these problems were

improved somewhat. Modern fo rk bushings are made of steel, coated with bro nze, and then coated with Teflon" (DuPont's

version o f po lytetrafluo roethy lene o r PT FE)-more o n

Teflo n in a mo ment. These provide a dramatic improvement

in bo th frictio n and wear. T he bro nze layer is a built-in safety

designed to provide an adequate surface when the Teflon wears

through. The biggest reason they need to be replaced is they

get imbedded with metal shavings and o ther comaminams.

O ther causes of damage are: disassem bly, dem ed sliders, and

rarely, pure wear.

DYNAMIC FRICTION Once the static frictio n between two compo nents is

overcome and they begin to slide, we en ter the wo rld of

d ynamic fric tio n. Let's look at an example of static versus

d ynamic frictio n. You a re on an icy street and there is a Ii ttle

o ld lady in a ' 62 Cadi llac right next to you. Of course you

want to impress her, so when the light turns g reen, you nail

the th rottle. The little o ld lad y pulls away fro m you like you

a re standing still. This is because you broke static fric t ion

a nd lost tractio n by going in to d ynamic frictio n.

So which is greater-static o r dynamic friction? All

things being equal, static frictio n is greater. " Hooked up"

is grea ter than "broken loose." And in general greater slip

ve loc ity will decrease the friction slightly. T h is is the reaso n

that when yo u push o n your fo rks, it is harder to start your

fo rk wbes compressing than to keep them compressing.

The exceptio ns to this general rule are again tires, especially

ce rtain compo unds, where a little slip can acw a lly create

more frictio n than hooked up but only a little.

Some people think that if you want to go fast o n an

o ff-road mo to rcycle, higher revs and throwing a lot o f dirt

are the way to go. This is o ften no t the case. Fo r example,

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Jean Michele Bayle, at the 1996 U.S.G. P. at G len Helen, won the race with a flat front tire. He hau led around the corners

and only threw up a tiny roost. Everyone chasing him was th rowing up roost that was literally knocking spectators over. JMB pulled away a seco nd a lap with a flat front tire, and he looked like he was our for a Sunday ride .

We're often foo led in motocross because we've got knobby tires digging into the d irt. Most road racers know that when

they are just barely spinning is actua lly when they have the most traction. W hen they're spinning a !or, they're nor going as fas t as they could (and it's pretty hard o n tires too).

T his is very noticeable in racing shifter karts. Lee attended Yamah a's press introduction for its on- and off- road

racing reams in 2002, and everyone tried their hands at go­kart racing. Ir was fascinating to watch the pro supercrossers powersliding through the turns bur always being one to three seconds a lap slower rhan the factory kart racers. The kart pros knew rhar roo much slid ing- though very cool looking­

a lways cost more ri me than keeping the tires hooked up and propelling rhem forward.

COATINGS Hard anodizing is a coating rhar is applied ro aluminum and is quire different than color anodizing. H ard anodizing makes the surface dramatically ha rder, more durable, and more

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4.5 When a front wheel hits a bump with the brake off, the force goes radially to the front axle al an angle as shown. This force can be broken up into components: first is a component that tends to compress the fork and second a force that tries to bend it in half. The fork bends mostly just below the triple clamp where there is the most leverage. This creates a temporary "kink" that the upper fork bushing has a hard time getting through, causing binding and excessive wear.

sli ppery. Ir is com monly used on aluminum fork sliders and shock bodies and is fairly inexpensive.

The quali ty of the hard anodizing can be qui re varied. The less expensive methods can wear our fairly easily. Once rhe coating is gone, the soft aluminum is exposed and the fo rk has much grea rer fricrio n.

Let's go back to the upside-down forks with the kink in rhem. W ith rhe forks disassembled, inspect rhe cond ition of

the anodizing on the inside of the outer fo rk rubes. Take an inspection mirror and a flashlight or a bore scope and inspect fo r wear right where rhe lower triple clamp would be. Using

an inspection mirror is a must: if you don't use an inspectio n mirro r and just look down the rube, you will likely see only reflections and you'll miss the wear. If the anodizing is worn rh rough bur they're nor too bad, rhe rubes can be stripped,

hard anodized again, and polished. Exotic coatings like titanium nitride and DLC (Diamond

Like Carbon) can further decrease friction. T itanium nitride

is nor used much anymore because DLC is slipperier and more durab le. These coatings can get pret ty expensive (DLC for a pair of rubes is in the $600- $800 range), bur if you are looking for the edge, go for it.

An im portant rip on DLC coatings is tha t the newer the fo rks are the better. T his is because rhe fo rk rubes have to be unscrewed from the fork bottoms, coated, and screwed back

o n. If you've got old fork bottoms, you can gall and destroy a perfeccly good sec of fo rk borcoms by caking them apart. T he o lder they are the more chance of damage.

Teflon has been used in many fo rms with good success. T his dry film lubricant can reduce friction d ramatically. Teflon can be fur ther combined with o ther friction reducers like molybdenum disulfide (moly) . le can be combined with o ther materials to bond it co su rfaces. Ni-Tef(nicke!Teflon) is another coating with good resulcs. T he challenge ofall Teflon­based coatings is that they have a tendency co wear ou t with use. Boch Teflon and moly have been added co suspension fluids wi th limited success over the years. One problem is that they have a tendency co settle co the bottom of the fork when no t in use, just like non-stick cookware at ho me.

POLISHING Surface roughness has an effect o n friction, though it is

smaller than most people might chink. Doubling the surface roughness might cause only a few percent change in fr iction. T his doesn't mean surface roughness doesn't matter- it does, and effo rts to reduce friction can really pay off.

T his is particula rly true on o lder right-side-up dam ping rod fo rks; both the outer slider and rhe inside of rhe chrome cube are eligible. Ar Race Tech we have a small-bore engine hone (nor a ball hone) rhar we wrap wirh 500-grir sandpaper and run with a drill motor to polish.

Polishing the inside of a cartridge tube is pretty simple. Ger a %-inch (I Omm) stee l rod ar your local hardware store. Take a hacksaw and cur an axial slot in the end of rhe rod.

Next prepa re strips of cloth abo ut 25mm (I inch) wide. Put one of them in rhe sloe and wrap up enough layers so rhar when you stick ir into rhe rube it has some compressio n on ir. Put rhe rod in a hand drill . Wee rhe clo th and apply some automotive polishing compound. Polish until you see rhe finish you're looking fo r.

SURFACE TREATMENT T here are surface rrearmenrs available today rhac are considered ro be "best kept secrets" by many race reams.

T hey go way beyond simple polishing. My favorite is fro m a company called WPC Treatment. WPC is nor a coating, iris a treatment rhac enhances rhe surface ro reduce friction and strengthen parts. Ir is widely used on engine parts, including

p istons, cranks, gearboxes, and all parts of rhe drive rrai n. We use ir in suspension components, particularly fo rks where fric tio n can be a large part of rhe coral fo rce.

The WPC process fi res ultra-fine particles coward the surface of a p roduct at very high speeds. T he resul ting thermal discharge permanently changes the surface, s trengthening structure and creati ng a harder more durable part. Materials like Teflon can o ften be added and subsequencly imbedded in rhe surface for further friction reduc tion. I use this treatment in rhe engines of my record-se tting Bonneville land-speed racing motorcycles with great success.

As I mentioned earlier, rhe main thing to know about friction is: friction ... bad! As far as suspension components are concerned, rhe less friction you have on slid ing surfaces, rhe better the suspension works. Look for any clues to

excessive fric tion (check the sciction zone in the sp rings chapter) and do your best to eliminate the cause. Mose of this chapter has been discussing front telescopic forks, as they have much greater problems with friction than rhe rear, bur attention ro rhe free operation of rhe linkage, swingarm, and shock can pay large dividends in performance as well. See rhe troub leshooting sectio ns on sticky fo rks and sticky shocks fo r more ideas for friction reduction.

Ir is interesting ro note rhar there have been rimes we have removed a lot of friction from a set of fo rks and as a resulr, they starred ro bo rcom. As you might guess, rhe

solu tion was not to add the fr iction back in! We added stiffer

springs, more compression damping, higher oil level, and so o n until the boccoming was eliminated and the ride was

dramatica lly better. Materials and lubricants affect both static and dynamic

frictio n ro different degrees. I highly recommend using the finest suspension fluids available as they can make a significant reduction in friction for a nominal cosr.

Ar rhe rime of chis writing, I have nor seen afrermarker

fo rk seals char outperform the original equipment. They are either stickier or they leak-or both- bur some are pre tty close ro OEM in performance. Also you should pre-lube you r seals wirh a high-end seal grease like Ultra Slick Grease. In a pinch you can use fo rk fluid, bur rhe seal grease lases lo nger.

Ir is my opinion char friction reductio n is an area rhar wi ll dramatically improve in rhe coming years. Remember­reduce friction first , then go ro springs, then damping.

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Chapter 5 Geometry When we as riders talk abo u t handling, wha t we're

really talking abou t is a fee ling that comes from a combination o f chassis geometry, chassis rigidity, engine characteristics (power, width o f powerband, and flywheel inertia) , mass distribution (center of gravity both horizontally and vertically), mass centralization, tire characteristics, ergonomics (handlebar, seat, and footpeg location), and suspension . These quantities interact and overlap. It can get very con fusing, however, because a change in flywheel inertia, for instance, can fee l very similar

82

self-correcting torque self-correcting torque (M) = L x F

to a change in compression damping. To understand this a li t tle better, let's take a close r look at a majo r component­

chassis geometry. Geometry refers to the physical relatio nshi ps of the

chassis components. So me of the many factors are the wheelbase, wheel diameter, rake (steering head angle) , fork offset, swingarm angle, countershaft location, sprocket sizes, center of gravity loca tion, and so on. From these we can calculate boch fronc and rear t rail , anti-squat angle, and anti­squat percentage.

5.1 A caster has a vertical pivoting axis. This means the

amount the wheel follows behind the axis is a direct measurement of trail. This trail creates a se~-correcting torque when the wheel is out of alignment.

Ir is worth repeating rhar geometry and suspension setup are interdependent. In o ther words, they work together as o ne affects rhe o ther.

TRAIL T he big daddy of all geometry numbers is front-end trail. Ground rrail is rhe distance from rhe center of rhe tire contact parch to rhe point where rhe steering axis intersects wi rh rhe ground. Ir is measured along the ground. In o ther words, it is the amount the contact patch "trails" the steering axis.

Let's look at a caster on a grocery shopping cart as in Figure 5.1. In this case rhe rotating axis is vertical and rhe rearward offset is a direct measurement of trail. I f rhe wheel ge ts ou r of line, there is a torque that self-centers the wheel. Grou nd trail o n a suspended fro nt end is most commonly measured with rhe suspension fully extended.

W ith a telescopic fron t end moun ted at an angle, it becomes a bit more complicated (Figure 5.2) . T he fact that the steering axis is at an angle creates trail even with no offset. Rake, also known as caster angle, is defined as rhe angle of rhe steering axis from vertical. Offset is the distance perpendicular to the stee ring axis rhe front ax le leads the steering axis. Testing has shown that with typical rake angles of 23 to 28 degrees o r more, zero offset actually creates too much trail. Forward o ffset (from now on simply called offset) is added in rhe tri ple clam ps a nd front ax le to decrease rhe trai l (Figure 5.3).

T he more crail a bike has, che greacer che self-cencering effecc of che front wheel. This gives the bike more stab il ity, but it's harder to turn che bars. W ithin a usable range, more

trail generally provides more grip (traction) when cornering. Most people have chis concepc backwards, thinking more

zero offset trail zero offset at the triple clamp and axle create excessive trail, result ing in stable, but very heavy steering

offset means a longer wheelbase and therefore more stabili ty. While rhe wheelbase does grow with increased offset, rhe trail actually decreases a nd therefore stability decreases.

If rhe rake is increased, so is rhe ground tra il (Figure 5.4). Conversely, if rhe rake is decreased, the ground trail is decreased. T his decrease in rake and trail also occurs dynamica lly (when the bike is being ridden) whenever rhe front end dives, such as du ring braking.

All rhar is necessary to calculate ground trail is three th ings: rake, wheel diameter, and total o ffset (triple clamp offset + ax le offset). T here is a free spreadsheet trai l calculator on www.racerech.com in rhe Seminar Student Downloads section. Keep in mind that when any of these parameters are changed, it affects o ther geometry numbers. For example, chan ging rhe front wheel d iameter will change both rake and trail as well as rhe center of gravity, swingarm angle, and rear anti-squat, among other things .

If you s tart measuring wheel diameters, you will find that tires wirh the exact same size markings will be different d iameters, sometimes dramatically so. T his means changing tires, par ticularly changing brands of tires, can have a significant effect on handli ng.

Ir should be noted char, as of chis p rinting, mosrsupermoto bikes have terrible ground trail numbers. T his requires rhe rider to "back it in." When I first measured Micky D ymond's KTM back in 2006 and saw ground t rai l numbers of92mm,

I immediately started making triple clamps to correcc it . He went on to win the Nacional C ham pionship and the Pikes Peak H ill C limb. Next we worked with Darryl Arkins and

Benny Carlson on the works Aprilia Team with similar resu !rs. An improveme nt of one to one and one-half seconds per lap

excessive trail

5.2 ~ the wheel is placed right on the steering axis with no offset and a positive rake is added, it creates too much trail.

83

steering axis

ground trail the distance between the center of the contact patch and the steering axis measured along the ground

more trail means more stability and more force is required to turn the bars

less trail means less stability and less force is required to turn the bars

I

I I

I I

~I o n a 45-second lap cime crack is noc unco mmon, even fo r

riders of chis caliber! Riders o f lesser skill quice o fce n see chree

co four seco nds per lap. T his is a very big deal.

REAL TRAIL We have been calking abouc ground crail. Bur che re is a bercer

way co measure crail-rea l crai l (Figure 5 .5).

T rail is a measurement of rhe length of rhe lever a rm

char provides rhe self-centering torque on rhe front whee l.

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ground trail

center of contact patch moves forward

less trail

5.3 Trail (or ground traiQ is the distance the center of the front wheel contact patch trails the steering axis measured along the ground. An increase in offset moves the contact patch forward, decreasing trail.

Torque is simply a ro tationa l force around an axis. To rque =

fo rce x lever arm length (the perpend icular d istance rhe

fo rce is applied from the rorari ng axis). T he key word here is perpendicula r. Ground trail is measured a long rhe gro und,

no r perpendicular ro rhe steering axis. Real crail, on rhe ocher

hand , is rhe discance from rhe steering axis co rhe cen ter o f rhe

rire contact parch measured perpendicu lar co rhe steering ax is.

T his is a much beccer merhod . T har being said , grou nd rrail

can be valuable as a comparison merhod if wheel d iameter

steering axis

rake the angle between the steering axis and vertical

some manufacturers measure this from horizontal

more rake means more trail because the steering axis is further ahead of the contact patch

and rake are held consranc. This concept of rea l trail was first

introduced to me by Tony Foale, a highly respected frame designer, author, and engineer. He also does an in-depth analysis of anti-squat (covered brie fly lacer on in chis chapter) in his book Motorrycle Handling and Chassis Design.

Trail is most commonly measured with rhe suspension fu lly extended, bur when the motorcycle is being ridden, trail is consrandy changing. T his is due ro both the movement

5.4 When the rake is increased, the trail increases.

I~

of rhe suspension componencs and rhe changing terrain. For example, when a dirt bike is being ridden in sand at slow speed, rhe wheel is pushing sand in fronc of it (Figure 5.6). The effect is char rhe center of the tire contact parch is moved forward and rhe trail is dramatically decreased. In fact, ir can easily produce negative trail, which is dynamica lly unstable. This explains why you feel so uncoordinated at slow speeds in sand (yes, it's really the bike, nor you ). O nce rhe bike gets up

85

real trail the perpendicular distance between the steering axis and the center of the contact patch­N OT measured along the ground

co speed it gees "on cop" of che sand, che contact patch moves

backward , and everything feels stable again . If we look at a supercross rider in a washboard whoop

section (whoops chat are close together), you can imagine it is important co gee "on cop" of the whoops . If the rider slows

down enough and lees the front wheel drop down into the bumps, the tire contact pacch moves fo rward and the crail

goes negative (Figure 5.7). W ith chis in mind, you can understand che importance

o f hicring che bump scraighc on, wi ch che wheel square co che bump-if you don't, look out! le is a cough technique co learn o r teach, but che fas ter che rider goes, the easier it gees. A word of caution here: the answer is not, "Just pin it, Billy!"

If you've seen a cop rider like James Stewart go through a washboard whoop section, you've seen chis in action .

Something else co keep in mind is chat suspensio n setup has a huge effect on t rai l when riding. Ifrwo identical bikes a re sec with the same initial (extended) crail and o ne

has a sofcer sec of fo rk springs o r even less preload, it will have less rake and cra il when in use (dynamically) . This is

because rhe forks will compress more-particula rly when gecring on rhe brakes going into cums.

REAR WHEEL TRAIL Rear wheel trail is rhe perpendicular distance from rhe steering ax is to rhe center of rhe rear wheel contact parch. In rhe past most people have referred to wheelbase alone, again measured a long the ground or more commonly from rhe centers of rhe front and rear axles. T he longer rhe rear w heel trail rhe

86

5.5 A far better way lo measure trail is "real" trail. Trail gives us an indication of the length of the lever arm of the self-centering torque. Bui the length of the lever arm of a torque should be measured perpendicular lo the rotating axis. Real trail is measured perpendicular to the steering axis.

slower rhe rear end "comes around," giving more straight-line

stability ar the expense of turning slower.

ANTI-SQUAT O n the rear, swingarm angle and chain forces combine co cause stiffening or soften ing of che effective rear spring rare during acceleratio n or deceleration. This effective stiffening is ca lled anti-squat as it "holds up" the rear end of the

motorcycle during accelera tion, keeping it from squatting. Ir is a tra nsient (temporary) effect linked to acceleration, and the effect increases with greater accele ration. The complete analysis can get quire involved, so in the scope of chis book we will provide a simplified overview.

To begin lee's look at how a motorcycle is driven

fo rward. Power is applied co the ground a t the rear t ire. T he rear tire is connected to the chassis through the rear axle and the chain. Forward d rive is transmitted co the chassis by the

rear axle directly in a straight line co the swingarm pivot (nor in a stra ight ho rizonta l line). T he swingarm pivot is the

point at which chis fo rce is applied, meaning char rhe angle of rhe swingarm where iris attached to rhe frame determines rhe direction of chis force.

Now we need to step back and look at a lirrle physics. When we apply a force to a body, rhe body reacts based on the mass of rhe body, rhe point of application, and rhe size and direction o f rhe fo rce in relation co che body's center of gravity. If che fo rce is applied in direct line with rhe CG (center of gravity) there wil l be no rotational force (torque) applied (Figure 5.8). If the force line does nor go direcrly through the

steering axis

CG, a rotating torq ue is generated (Figure 5.9). In addirion, rhe force can be applied anywhere along the fo rce li ne, and rhe body will react exactly the same way.

Imagine we hold rhe sprung mass of the motorcycle and rider at the CG. If the swingarm slope is posit ive (the

5.6 When going slowly in sand, the sand gels pushed up ahead of the wheel. The center of the contact patch moves forward. This decreases trail to the point of becoming negative and unstable.

5.7 Letting the front wheel drop into supercross whoops causes the contact patch lo move forward, decreasing trail, quije often lo negative.

cou nrershafr is above the rear axle), the swingarm force will rend to li ft rhe sprung mass. If this li ne of force does not go through the CG, it wi ll also create torque.

Now ler's add the chain (Figu re 5. 10). I r can only pull on rhe counrershafr sprocket. If rhe chain slopes down from

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force applied inline with center of gravity causes linear displacement, i.e. no rotation

/

/ /

/

the cou ntershafr sprocket to the rear sprocket, it will tend to pu ll the sprung CG down, making it softer. If no t a ligned with the CG, it will rotate the sprung mass as well . All this constantly changes, of course, as the rear suspension moves.

W ith some mathematical analysis we can figure our the effect of each of these components on the chassis independently, bur what a pain!

Fortunately there is a simpler way to analyze the rear end anti-squat graphically (refer to Figure 5. 11 ). Force vectors o n rigid bodies are sliding vectors. T his means we can apply both these forces anywhere along their lines of action. This means if we can locate the intersection point of the swingarm

axis and the chain axis, we can apply bo th of these fo rces there. This intersection point is called the instantaneo us force center (IFC). To be clear, it is the point at which we can

combine the two fo rces and represent them with one force (resultant force) that has the same effect on the chassis as the two individual fo rces.

Now lee's reattach the rear wheel to the motorcycle. We know the force comes in via the rear tire's contact patch with

/ /

/ /

force applied offset to the center of gravity displaces AND rotates due to torque (M) = (F x L)

/ /

/ /

/

/ /

5.9 When a force is applied in a line that does not go through the CG, the body not only displaces, it also rotates.

88

/ / 5.8 When a force is applied to a body inline with the CG, the body displaces with no rotation.

center of gravity (CG)

the ground and goes through the IFC. This gives us two points to draw the line.

The angle of this force line fro m the center of the contact patch through the IFC from horizon cal is called the an ti-squat angle. It is the exact same angle we would have calculated as the resultant force of the chain and swingarm had we not done a graphical analysis. T his makes the analysis much simpler because we know chat the resulcanc horizontal component of the force is the driving fo rce at the rear tire contact parch . If we also know che angle, we can calculate the vertical component wi th trigonometry (F = Fd . . x cos (anti-squat angle]). We

vert riv ing

know the point of application is the IFC, so the rest of the

ana lysis practically does itself (just kidding). Referring to Figure 5.1 2, you can see the anti-squat angle

changes with swingarm angle. If the line of force through the IFC goes through the combined CG, it will not create a rotating to rque, but the vertical component will tend to li fe the motorcycle. If the line passes below the combined CG, not only will it lift the motorcycle, effectively making the suspension stiffer, it will also create a torque that rotates the chassis backward {counterclockwise viewed from the right) , loading the rear suspension. This torque is counterclockwise, so it will tend

to compress the rear suspension, effectively making it softer. To clarify, chis torque counteracts some of the life. As long

as the anti-squat angle is positive, it will still life the motorcycle but not as much as if it were going through the CG. In this case the combined lifting and rotation tend co cancel each ocher somewhat-as long as che lifting is greater (the anti­squac angle is positive) , there is still a nee anti-squat effect. Notice chat as the suspension compresses fu rther, the anti­squac angle gees smaller. As long as che anti-squat angle is still positive, the nee fo rces will continue co hold up the motorcycle

during accele ration, though to a lesser degree. H ere's when we need to make some assump tions so chis

doesn't gee hai ry (is it too lace?) . Lee's assume 50/50 weight distribu tion. Lee's also assume the height of che combined CG {center of gravi ty) of che sprung mass of che bike and rider is ha lf rhe wheelbase. These assumptions are pretty close to reality for many motorcycles and will help simplify rhe calcula tions.

W hat we need to figure out is how large the forces are,

realizing that they vary dependent o n ho w hard the bike

accelerates. A modern 1 OOOcc sportbike has enough power

and tires are good enough to accelerate at l g-the acceleration

o f gravity. Yes, I realize gravity is a vertical acceleration and

5.10 When the motorcycle accelerates, the sprung mass is being pushed by the swingarm and at the same time pulled back by the chain. Both these forces can be broken into vertical and horizontal components. The sum of the horizontal forces is the force of acceleration.

5.11 The instantaneous force center or IFC is located where the axes of the swingarm and the chain intersect. The anti-squat angle goes from the center of the rear contact patch and goes through the IFC. The greater the angle, the greater the anti-squat.

this is a ho rizon tal acceleration, but this will help simplify

things as well.

Recall Newton's Second Law of Motion, F = ma o r force

equals mass ti mes accele ratio n . The mass being accelerated

is the co mbined sprung mass of the bike and the rider.

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5.12 As the suspension goes through the travel, the amount of anti-squat decreases.

W hen che bike is ac resc chis combined sp rung mass is being

acceleraced by gravicy vercically downward. In o rder co

accelerace ho rizoncally, chis same mass muse have a ho rizo n ca l

force applied .

Because we locaced che CG ac 50 percent o f che wheelbase

bo ch horizon rally and vercically, ch is means when we accelerate at

l g, the fro nt wheel will jusc barely lift off the ground. See Figu re

5.15 . Here's why: when che bike accelerates, it wanes co rotate

councerclockwise arou nd che rear tire concacc patch, tending co

cause a wheelie. In other wo rds there is a corque or moment

(force x lever arm) around the concacc pacch equal co che force

d ue to horizontal acceleracion cimes che heighc of che CG. On

che ocher hand che clockwise corque thac cends co keep it o n che

ground is equal co che weighc (suspended mass cimes acceleracio n

of gravicy which is vercical) cimes half che wheelbase.

Because che heighc o f che CG is equal co half che wheelbase,

che lever arms are che same lengch. And because che vercical

acceleration of gravi cy is equal co the l g ho r izoncal acceleratio n

we have chosen, bo ch o f these corques are equal. Ifwe acceleraced

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any harder, che front end wou ld lift o ff the ground and wheelie

over. T h is is because the ho rizon ta l fo rce would become greater

chan che weighc chereby increasing che councerclockwise co rque

co an amo unt g reacer chan che clockwise corque.

W hen the fra nc wheel lifcs, che rear suspensio n muse

hold up all che weighc of che bike and rider inscead of jusc

half. If we wane che suspensio n co be independent o f chis load

cransfer, che anci-squac force from the swingarm and chain

muse be equal co che added vertical load. T his means che

upward vercical com ponent must equal half the horizontal

fo rce due co che acceleracio n of che bike.

If the anci-squac line goes through the CG of the sprung

mass o f che bike and rider, che upward anci-squac force will

equal che ho rizontal driving force. This is twice as much as we

need co isolace che anci-sq uac force. We call chis che 200-percenc

anci-squac line. To make a 100-percenc anci-squac line, we must

draw a line with half the slope (na e half the angle). T his will

give us half che vertical fo rce, which is exactly what we need fo r

the rear suspensio n co move freely wichouc lifring or squateing.

force from rear wheel

5.13 If the anti-squat line goes through the CG, ~will lift as much as ~ pushes forward. This undesirable scenario is avoided by the manufacturers.

5.14 When the anti-squat angle is below the CG, the vertical lifting component decreases.

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To graph this we draw a vertical line th rough the front

axle. The 200-percent anti-squat line wilt in tersect this line at

twice the height o f the CG. T he 100-percent anti-squat line

will intersect it at the height o f the CG and a 0 -pe rcen t anti­

squat line intersects it a t the grou nd . See Figure 5.16.

As you can imagine, the anti-squat angle and percen tage

changes constan tly as the suspension moves and as the rider

sits, stands, hangs off, or tucks. T he more suspensio n travel, the

more the change. So the next question is: what anti-squat is

best? If there is way too much anti-squat (200 percent o r so), the

F1 = F2

L1= L2=~ lhltllot•.

5.15 We have arbitrarily (and realistically) chosen the CG location of half the wheelbase high and in the middle of the wheelbase. If we accelerate at 1 g, the front wheel will just begin lo lift off the ground transfering all the front wheel load onto the rear suspension. To separate the driving forces from the suspension we need to support this extra load with anti-squat force.

combined rider and motorcycle center of gravity

I I I I

:/ / 1

I I

~ ·~

100% anti-squat

0% anti-squat

negative anti-squat

5.16 If the anti-squat line passes through the CG, it will have twice as much anti-squat as we need so we call this 200-percenl anti-squat. The 100-percenl line would have half the slope. For the 50/50 weight distribution scenario we have chosen, the 100-percent line would intersect a vertical line coming up from the front axle al the CG height.

92

suspension can actually top out under acceleration. !fir does, it no longer has the abili ty to fo llow the ground, and the resul t is a loss of traction and a stiff ride. On a dirt bike the ab iii ty to stiffen the rear suspension with the throttle has a couple benefits. T he first is when landing a jump, and the second is getting lift on the takeoff of jum ps for clearing doubles, and other big obstacles. In order for this to occur with any significance, the anti-squat must be 100 percent or more.

T he downside to anti-squat above 100 percent on a dirt bike comes when accelerating over small square-edge bum ps, particularly when exiting a turn . T his anti-squat dynamic can add considerab ly to the harsh fee li ng that these types of bumps naturally create.

When anti-squat is less than zero, the forces tend to pu ll the wheel off the ground. T his situation is rare for street bikes as swingarm angles rarely go past horiw ntal, bu t it is not that uncommon fo r dirt bikes because they have lots of travel.

When the anti-squat percen tage is less than 100 but above zero rhe sprung mass is not fully supported and the rear end will squat some. T he lower the percentage, the more it will squat during acceleration. This squatting action creates counterclockwise rotational momentum and wi ll use up more travel leaving less travel available to handle rhe bum ps.

Remember that the an ti-squat percentage is more important wirh bikes that can accelerate harder, specifically the bikes with higher "power-to-the-ground-ro-weighr-ratio"

like liter road race bikes. T here is a distinct advan tage to

anti-squat percentages slightly above 100 percen t: when the throttle is opened on a liter sportbike, the momentary push against the ground can actually increase tractio n. Too hard a push, however, causes rhe CG ro move upward, pu lling rhe

tire away from the grou nd and ultimately decreasing traction moments thereafter. This means rhar both too little and

particularly too much anti-squat can decrease traction. T he critical areas for anti-squat are acceleration during

corneri ng, when accelerating from a dead stop, accelerating ou t of turns on a di rt bike, and on jumps and whoop sections.

When a manufacturer designs a bike, ir attem pts ro minimize the change in anti-squat throughout rhe suspension travel. This is rhe reason coun tershaft sprockets are so close to the swingarm pivot. O n the tun ing end, we need ro know

what things change anti-squat and which way we need to go.

GEOMETRY MEASUREMENT T here is an old saying rhar says you can never get where you want to go u ntil you know where you are. This maxim ho lds true for tun ing as well: you can't achieve the resu lts you're after

until you have an accurate assessment o f your starring point. In our opinion, rhe most sophisticated system for

chassis measurement our today is GMO Compurrack (www.gmdcompurrack.com). I r is a precise optica l device rhat nor only measu res geometry bur a lso al ignment, includ ing twists and offsets. I r is used by many factories for rhei r race reams as we ll as fo r research and development.

The GMO Com putrack Network specializes in measuring, straigh tening, and optimizing (serting up the geometry) of all types of motorcycles. T his is a really good place to start, as a tape measu re and protractor just do n't cut it when it's time to tune. If you use the complete services offered by the GMO Computrack network, it wi ll use its sizeab le database of knowledge to get you where you want ro go.

Do not get thrown off if a tuner uses ground trail and swingarm angle only. Keep in mind that, when com paring app les to apples, these are valid tuning parameters. However, when comparing different machines, they do lose some of their validity.

GEOMETRY TUNING If you wan t ro tune on your own, it is still viral to know yo ur starting point and make known, incremental changes. Also bear in mind that it is impossible to change one thing wi thout affecting o ther aspects of the suspension or geometry. A suspension setu p change can have a very similar result ro a geometry change. The results obtained by changing the fork preload could be very similar to those you get by altering rhe fron t end ride height (repositioning rhe tubes up or down in the triple clamps).

To Increase Front End Trail • Adjustable fork borroms-move the axle back

• Triple clamp offset (adjustable or fixed)- decrease offset (move rhe fo rk rubes back) , 2mm increments

• Larger front tire outer diameter • Raise rhe front end by sliding rhe fo rk rubes down in rhe

triple clamps o r increasing fork spring preload (less fro nt end sag) (increases rake), 5mm increments

• Lower rhe rear end with shock length, rear wheel outer

diameter, o r running more rear sag (increases rake) 5mm increments

To Increase Rear Anti-Squat • Raise rhe rear end (increase the swingarm angle) with

adjustable rear shocks or frame ride height adjusters, or lengthen the shock internally

• Smaller countershaft sprocket-note that th is can also affect the swingarm length

• Larger rear sprocker-nore rhar rhis can also affect rhe swingarm length

• Raise swingarm pivot in rhe frame o n models wirh available inserts (2006-09 GSX-Rl 000, ere.)

• Shorten effecti ve swingarm length by shortening rhe chain or with gearing and rhe chain adjuster

• Lower rhe CG by getting in a ruck • Move CG forward by sirring further fo rward o n sear • Raise rhe front end ride height (nor preferred as this has

more effect on rake and trai l) • Smaller rear tire outer diamerer-rhough rhis generally

makes only a very, very small difference

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A few things to keep in mind: First, more is no t necessarily

better. Second , when in doubt consult with the p ros. Third,

just because everyone else is doing it doesn't m ean it's the best.

Fourth , just because everyone else is do ing it doesn't mea n it's

wrong. See the troubleshooting chapter fo r gu idance.

WEIGHT BIAS Weight b ias refers to the amount of fo rce o n each o f the tires

either laden (rider o n board) o r un laden, no rmally disp layed as

a fro nt-to-rear percentage o r ratio . For exam ple, 48/52 would

mean 48 percent o n the fro nt and 52 percent o n the rear. T he

amount of tractio n available is direccly related to the amount

o f force between the tires and the ground . (See the Traction

Control appendix.)

Most modern sporcbikes have a slight front end weight

bias, 5 1 o r 52 percent. W hen a 7 4kg ( 162 lb) rider is put

o n board , it becomes very close to 50/50. Mose modern

dirt bikes have slightly less front end weight bias, 48 to 50

percent. When the rider is pu t o n board (stand ing o n the

pegs), the sh ift is also rearward so chat fro nt end bias dips to

44 to 46 percent with a 74kg rider. T his means chat, for both

sport and motocross bikes, m o re of the rider's weight is o n

the rear wheel-heavier riders wi ll au tomatically have a mo re

rearward weight bias than lighter o nes.

The most effective way to shift the weight bias is with

rear axle positio n. The further the axle is moved back, the

m ore load is shifted to the fro nt. M oving the rider position is

also effect ive. O n a road race bike a few layers o f padding o n

the back of the seat/rear tail section can shift the rider fo rward

significantly. O n a dire bike the rider has m uch mo re roo m to

m ove about, and the habit of choosing a seating locatio n has a

huge effect o n potential lap times. Most riders, particularly as

they gee o lder, have a habit of s itting coo far back. A stepped

seat can help remind a rider to sit fo rward.

Many things have been said about methods of "weighting

the fron t end." Lowering the front is probably the most commo n

and , while it is true chat a change does occur, the change is

miniscule. I know, I know, you've tried it and it wo rks! You can

feel more fo rce on your palms. I would invite you co use an

accurate scale or load cell and check out the actual d ifference

yourself. Another common step taken is lowering the bars:

again, the difference is slight. T he reason you feel it mo re is your

upper body is rotated forward and you are supporting more of

the weight o n your hands. Granted, there is a tiny change, but

you haven't significandy shifted your weight fo rward.

Awareness o f the effect o f we ight bias can be part o f a

successful se tup, and understanding what changes are effective

can save a lo t o f time.

SOMETIMES VELCRO IS THE ANSWER

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In 19961 participated in the 54th running of the famous 24 Hours of Montjuich endurance road race at the Circuit de Catalunya in Spain. Our team, which was made up entirely of motorcycle journalists, had four riders ranging from 5 feet, 5 inches to 6 feet, 3 inches. This created both an ergonomic

and weight distribution problem as there was no seat setup that worked for all of us. Our effective but not-so-elegant solution was to add adjustable foam layers connected with hook-and-loop fasteners and secured wi th duct tape. This allowed quick changes to compensate for my short T-Rex arms as well as the orangutan arms of my German teammate. When the checkered flag fell , our team finished 7th overall and 2nd in our class of 750 Supersport, just ahead of 250GP front-runner Carlos Cardus' team on a factory Ducati superbike. Viva la Velcro! - Lee Parks

Chapter 6 Troubleshooting and Testing I n this section of the book we have compiled a list of common

problems riders have with their suspensio n. T hese may be encountered on the dirt, street, o r track. To help understand rhe issues we have included diagrams rhar symbo lize our best effort to replicate three-dimensio nal movement in rwo­dimensional space. T here are three parts to the troubleshooting section: first is a quick pictorial overview of ideal suspension ve rsus real-world expectations give n current tech nology, second a simple description of what happens ar rhe extremes of possible suspension setup, and third the common problems associated with forks and shocks on bikes.

When going through possible solu tions, rhey are listed in order of easiest or more likely and go toward less likely. For example it might list an external adjuster change before an internal valvi ng change. Ir's a lor easier to change an adjuster than revalve internally though rhe internal change might be far more likely.

The Testing Procedure seer.ion (page I 06) is presented after rheTroubleshooring Scenarios. Ir is perhaps rhe most important

part of this book. If you have a good testing procedure, you will

be able to come up with good settings even as your depth of knowledge grows.

Use rhe illustrations and information as a guide to fi ne­runing yo ur suspension and make sure to use the Testing Form on page 25 1 to keep track of your results. Using this guide wi ll reduce the guesswork o f achieving a perfect ride and help make suspension troubleshooting eas ier and fun.

DAMPING EXTREMES 1. Too Much Rebound Damping (Pack ing)

T he suspension is held down in rhe stroke because it cannot rebound fast enough and each bump causes additio nal compression. T he ride becomes harsh because roo much fo rce is needed ro initiate more movement. T his also causes a loss of traction because of tire deflection.

2. Too Little Rebound Damp ing (Pogoing) In this scenario rhe suspension does no t control the stored-up spring energy, which causes a pogo stick- like effect. The uncontrolled vertical movement can rake rhe

wheel off the ground and cause a loss of tractio n.

never moves loom•~

Ideal

Reality The ideal ride has perfect wheel contact on both the front and the back of the bump while the sprung mass maintains a perfectly level path. The best real, world suspension isn1 qu~e there, but this is the goal.

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Extreme 1: Too much rebound damping

Extreme 2: Too little rebound damping

Extreme 3: Too much compression damping

Extreme 4: Too little compression damping

96

excess rebound dampillg resists extension, wheels lose traction

inadequate rebound damping does not control stored spring energy, causing sprung mass to rise too quickly

transmits too much bump energy to the chassis, which pulls the wheel off the ground

compression travel is lost, and requires excessive force to initiate movement

~tom'~--­- ~---

fails to manage bump energy, wheel deflects

3. Too Much Compression Damping (Harshness) Here che suspension causes che wheel co deflecc off che bump on impacc because chere is coo much res iscance co movemenc. This makes fo r a very harsh ride.

4. Too Little Compression Damping (Bottoming) T he wheel moves pasc che cresc of che bump du ring compression and is noc able co follow che backside of che bump, causing a loss of craccion. le fee ls mushy and can boccom easily.

TROUBLESHOOTING SCENARIOS Forks 1. Bottoms- Too Soft, Mushy

Ask quescio ns: I . Whac kind of condicio ns? (G-oucs, landing on

jum ps, face of jumps, ecc.) We are decermining whecher che velocicy is low or high.

2. Does ic feel good ocherwise? (If yes, go co A) 3. Does ic feel coo sofc everywhere? (If yes, skip A,

go co Band C) A. Oil level low-raise oil level-affeccs moscly che

lase YJ of era vel B. Noc enough low-speed compression dam ping C. Noc enough high-speed compression damping

Front 1: Front bottoms, mushy

Front 2: Front loo stiff

suspension bottoms

overshoots crest of bump

D . Spring race coo sofc E. Noc enough preload F. Dire in valving, broken valve, benc shim, burr on

che piscon/shim G . Cartridge rod bushing worn ouc (cypical problem

wich pre- 1996 KYB) H . Compression valve 0-ring broken, especially if

jusc rebui lc I. Cartridge rod noc attached to cap- broken o r

unscrewed-oops 2. Too Stiff-De.fleets, Harsh, Nervous, Twitchy

Ask quescion: Everywhere o r j usc on square edges? (Jusc square-edged: see B and C) A. Too much compression damping ad juscmenc­

high-speed and/or low-speed B. Too much compression damping internally-

change high-speed first, then low-speed C. Spring rate coo sciff D . Too much low-speed rebound damping-packing E. O il level too high F. See # 9 (sticky fo rks)

3. Poor Traction A. Poor cire cype/com pound B. Too much tire pressure

steering feels twitchy when tire loses traction

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C. T ire pressure way too low 0. Too much low-speed rebound damping E. Too much low-speed compression damping F. Not enough low-speed rebound damping G. Not enough low-speed compression dam ping H . Not enough weight on the front end

1. Swingarm too short 2. Rear ax le moved up too fa r 3 . Seat too far back 4. Bars too high o r too far back

I. See # 5 (pushes, no t enough trail) 4. Doesn't Turn

Note: This may be the most misunderstood and misdiagnosed

fork symptom. ft is quite often more a geometry issue than a

suspension issue though these overlap. Ninety-nine percent of

the time the tuner/rider drops the front end (raises the fork

tubes in the triple clamps) in an attempt to cure this. His

thinking is typically one of two things: either he's trying to

"weight the front end" or he is trying to decrease trail Does

dropping the front end weight the front end? Yes, but not so

much as you'd notice it. This is a common misconception.

As to decreasing the trail-the reason you'd want to decrease

trail is because it is too difficult to turn the bars. If there is

a lack of traction, you'd want to go the other way--increase

the trail. Along with an increase in trail generally comes an

increase in traction (grip). So, begin by asking the question:

Do che bars cum easily or is ic hard to turn the bars? Ifi e is easy to cum the bars start with #3 (poor traction) , then # 5 (pushes) If ie is hard to turn the bars go to #6 (excessive fo rce required)

A. Tire pro files too flat o r too wide, rim too wide B. Riding Position- no t enough weight on the

front end I. Seat too low 2. Bars too high

C. Riding Style (nor everything is the bike!) 1. Rider doesn't understand rhe concept

of counters teering 2. Noc weighting che front end 3. Elbow down riding style-wrong fo r dirt 4. Elbow up riding style-wrong for pavement 5. Sitting too far back, nor weigh ting the front

end-wrong fo r dire and pavement 6. Rider centerline to ou tside of bike cencerl ine­

wrong fo r pavement 7. Steering wich both arms-wrong for pavement

(steering should be done with inside arm only) 8. Noc looking through turn 9. Riding two-up-passenger nor leaning with

the bike 10. Riding two-up-no r enough weight on che

fron t, too much on che rear 11. Luggage added to che rear

0 . W heelbase too lo ng 5. Pushes (easy to turn the bars but the bike doesn't turn,

Low traction), Steering Feels Loose, Power Steering

(flat track term), Chatters When Entering a Turn, Runs

Wide Mid-Corner and Exit, Tucks (turns too quickly-­

this is not enough trail but not as severe as Pushing)

Note: this is usually a chassis geometry problem-not enough trail

tucking is when the bike steers too sharply with very little steering input

Front 5.1: Front tucks

actual path of front wheel travel

Front 5.2: Front pushes

98

A. Fron t end rides too low in comparison to the rear B. Raise the fron t e nd (slide fork tubes down in

triple clamps) C. Lower the rear end D. Fork spring rate too soft E. Not enough fork spring preload F. Low-speed rebou nd too high, causing packing G. Not enough low-speed compression dam ping H . Increase low-speed compression damping

adjustment or valving stack stiffness I. Go to a single-stage valving stack instead of two­

srage-dirt J. Anythi ng that makes the rear higher than the fron t

6. Takes excessive fo rce to turn the bars, p lenty of

traction, doesn't complete the tttrn

Note: this is a chassis geometry problem-too much trail A. Front end rides high dynamically in com parison to

the rear B. Lower the fron t end (slide the fork tubes up in the

triple clamps) C. Too much fo rk spring preload D. Spring rate too stiff E. Rear ride heigh t too low F. Ai r pump-replace fork seals G. Anything that makes rhe rear lower rhan rhe front H. Too much low-speed compression damping

I. Bars too narrow, uncomforcable bend

J. See #9 (sticky forks)

7. Dives under Braking-(steady state)

A. Wi th telescopic fo rks it should! Linkage-type front ends may no t dive or may even rise.

B. O n braking, the total dive is controlled by spring fo rces only (rate, preload and air slightly), no t dam ping.

C. Fo rk angle too Aat (choppered), too m uch rake D . Fo rk springs too soft Note: Damping affects the rate of dive and "overshoot" but does not affect the front ride height after any appreciable length of time. E. Too much rear ride heigh t

1. Ride heigh t adjuster too high 2. Rear preload excessive

8. Feels Loose

A. Not enough low-speed rebound damping B. Not enough high-speed rebound damping-big

bumps o nly C. Nor enough compression damping D . Spring rate too soft E. Steering bearings loose o r worn F. Swingarm pivot or linkage bearings loose or worn G. Tire pressure too low or way too high H. Fo rk Aex, chassis Aex, swingarm Aex I. Worn-ou t fluid J. Damping rod bushings worn out (pre- 1996 KYB

cartridge type fo rks) K. Worn-out rebound piston ring-very rare

~ -------------

Front 6: Front high effort to tum the bars

Front 7: Front excessive dive

steering tracks but requires excessive effort

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Front 8: Front feels vague

9. Sticky Fo1·ks

A. Misaligned fo rk tubes when viewed from the front (sp layed ouc o r wedged in)-axle clam p no c centered (most common)

B. T riple clamps bent

C. Bene fork rubes D. Bene axle E. Dented sliders

F. Upside-down forks with poor bushing design G. Outer cube anodizing worn through

H . Ai r pump- replace seals, particu larly ac che lower triple clamp

I. Seals no t bro ken in o r poor design (afrermarkec) J. Seals no t lubricated K. Poor quality o il L. Poorly designed fo rk brace or fork brace

adj uscment- righc side up fo rks M. T riple clamp coo eight-USO (upside-down) forks

feels harsh due to

Front 9: Front sticky forks

100

intended path of travel

N. Misaligned fo rk cube height 0. Fo rks not broken in- (twin-chamber)

P. Bushings damaged from dent or wo rn out Q. Metal imbedded in bushi ngs

I. Preload washers noc located properly-USO fo rks 2. Aluminum preload washers

3. Scee! spring spacer d ireccly on aluminum cap 4. Bottom-out system needs chamfering­

p re- 1995 KYB cartridge forks 5. Fork caps "shedding" on installation- burr

o n thread R. Cartridge rod bushing coo right

S. Spring guide rubbing on inner diameter of spring/ incorrect manufacturing o r guide growing from soaking in solvent-USO fo rks

T. Fork spring outer diameter too large-spring outer diameter grows du ring compression a nd can bind on inner d iameter of fork tube

10. Headshakes- (fast side-to-side movement of the bars)

A. C hassis not straight- twisted or o ffse t

B. M isalignment o f wheels-chain adjuster marks are off

C. Fork flex, chassis flex, swingarm flex

D. Worn-out o r loose steering bearing or

binding dragging

E. Not enough trail- not enough self-centering effect

F. Too much trail- returns past center then re-correc ts

the o ther way quickly

G. Oil level too high (street)-headshakes

du ring braking

H . Botto m-out mecha nism too lo ng o r too abrupt

(street)- headshakes during heavy braking

I. Not eno ug h low-speed rebound damping

J. Too much rebound dampi ng

K. Too much high-speed com pressio n dampi ng-

deflects o n bumps

L. T ire pressure roo h igh o r too low

M. Poo r tire compound o r type

N. T ire not mo unted p roperly o n rim, bent rim, or

cord no t straigh t

0 . W heel out of ba lance-bent rim

P. Brake rotor bent-head shakes during braking

Q. Fork mo unted fairing not aerodynamically balanced

R. Any type of aerodynamic imbalance

S. Anyth ing that makes the fro nt end lower than the

rear decreases trail

T. Too much steering swing inertia

U. See #9 (sticky fo rks)

V. Additio nal solutio ns

l . Steering damper-Scott's Performance has an

excellent damper

2 . Tighten steering bearings so that they drag

slighrly-poor man's steering damper

11. Chatters (Patters)-(ttp and down wheel movement)

Note: This can be a vibrations/harmonics problem where the excitation (input) frequency matches the natural frequency of the suspended system. ft is often confused with, and can cause, headshake. A. See #5 (pushes, no t eno ugh trail)

B. Not eno ugh rebound damping

C. Not enough compression damping

D . C hange spring rates stiffer or softer to change

natural frequency-start with stiffer

E. Too much compressio n damping

F. Too much rebo und damping

G . Ti re pressure-too much o r too little

H. Ti re design

[ headshake can be either self-energizing ... )

[ a stable oscillation ... J

[ or self-damping )

Front 10: Front head shake

101

--~~--~~-------...;.;-~-=-~~------:-

--~------------..... 2... oftmUoo J

actual path of travel

------------- ---- ...............................

....... ..... ........

Front 11 : Front chatter

I. C hassis/swingarm flex C. Too much preload J. Preload change-changes cenrer of pressure height K. See #9 (sticky forks)

D. Too much low-speed compression damping

12. Bottnces off the Grottnd onfttmp Landings A. Bottoms severely, loads the frame, and recoi ls

(see # 1, bottoms)

B. Noc enough high-speed rebou nd dam ping C. Noc e nough low-speed rebound damping

13. Deflects on Sqttare-Edged Bttmps, Roots, Rocks, Expansion joints, Sqttare Holes, "Botts' Dots" A. Too much high-speed compression damping­

eicher valving stack or piston o rifice restriction B. Spring race too stiff

k5;;1 Front 12: Front bounces on landings

102

E. Too much low-speed rebound damping F. Way too soft and bottoms severely

G. See #9 (sticky forks) 14. Leaky Seals

A. O ld seals B. Nicks in cube C. Worn bushings D. Bent cube E. Improper installation F. Fork cube too smooth G. Excessive brake dust (sintered metallic pads)

Front 13: Front deflects on bumps

15. Front Tire Wear-Road Race

A. T ire edge tear I. Improper tire pressure 2. See #5-chassis geometry issue, nor enough trai l

B. T ire center wear

Shocks

I. Too much ti re pressure 2. Front end chatter 3. Tire ou t of balance 4. Excessively stiff forks 5. Improperly adjusted steering bearings 6. Nor enough turns o n your way to work or

exhibition of speed-too much drag racing on the way to the pub.

I. Kicks Note: This is the most commonly misdiagnosed symptom

on a dirt bike. This symptom is umally diagnosed as not

enough rebound damping, however it is usually caused by

one of two things: 1) it's way too stiff or 2) it's way too soft.

Kicks# I-Too Stiff

I. Too much high-speed compressio n damping 2. Spring rare too sciff 3. Way too much low-speed compression damping 4. Too much rebou nd damping (nor too little) 5. Linkage bearings bad, right, dry 6. Too high tire pressure 7. Way too much preload 8. See #8 (sricky shock)

actual path of travel

------ ---- ..................... ....... ...... ...... ......

Kicks #2-Too Sofr

Severe Bottom ing (see #2, boccoms) 2. Bottoms

A. Nor enough low-speed compression damping B. Nor enough high-speed compression damping

(landing o n jumps) C. Sp ring rate too sofr D. Too much static sag E. Worn piston ring 0 -ring, piston ring, or body F. Suspension fluid worn out or poor quality (fades

when shock hears up due ro low viscosity index) G. Shafr seal b lown

H . Nor enough nitrogen pressu re, cavitation I. Blown bladder (usually caused by blown

shaft sea l)

J. Bent or distorted va lving shims 3. Swaps-Dirt

Ask q uestions: I . Does it fee l harsh/deflect? Too Stiff 2. Does it bottom out easily? Too Sofr

3. O ne bump or into a series of whoops? If it is on a series of whoops, it could be a rebound

problem. Too much rebound damping (packing especia lly on a series of whoops) or too li ttle high-speed rebound damping (uncontrolled rebound on a series of whoops).

A. Too much high-speed compression damping­deflecring, nor bottoming

B. Nor enough low-speed rebound damping-loose

103

excess compression damping means the wheel can't move

Rear 1: Rear kicks

spring or damping is too soft causing bottoming and kicking

Rear 2: Rear bottoms

Rear 3: Rear swaps

C. Not enough high-speed rebou nd dam ping-loose o n whoop section

D. Spring rate too stiff-deflects E. Spring rate too soft-mushy/bottoms F. Bottoming severely G. See #8 (sticky shock)

4. Feels Loose/Shock Pttmps A. Not enough low-speed rebound damping B. Not enough high-speed rebound dam ping C. Not enough low-speed compression damping D. Sp ring rate too soft E. Too li crle preload

5. Poor Traction

104

A. Too much low-speed rebound damping (main cause)

B. Too much low-speed compression damping C. Not enough low-speed rebound damping

(much too little) D. Not enough low-speed compression damping E. Too much tire p ressu re F. Poor tire rype/compound G. Tire worn ou t H. Shock heim bearings worn out {loose) I. Linkage bearings worn out {loose) J. Spring rate too stiff K. Not enough swingarm angle- not enough anti-squat L. Too much swingarm angle-too much anti-squat M. Too much preload N. Too much rear ride height {adjuster too high) 0. See #8 (s ticky shock)

------------- ____ .-

Rear 4: Rear feels loose

Rear 5: Rear poor traction

6. Squats on Acceleration

wheel follows surface but with uneven pressure at contact patch

·-

A. Too li ttle swingarm angle-not enough anci-sq uat B. Spring too soft C. Not enough preload (too much static sag) D. Councershaft sprocket too big-not enough

anti-squat E. Rear sprocket too small-not enough anti-squat F. Compression damping too soft-changes rate of

squat, not final amount of squat 7. Not Tracking

A. Too much low-speed rebound damping­poor traction

B. Too much high-speed compression damping­defleccing on square-edged bumps

C. Too much low-speed co mpression damping­skating, poor traction

D. Misaligned chassis

·-

.... .... - -C ~

8.

9.

poor acceleration

E. See Forks #9 (sticky forks) and Shock #8 (sticky shock, front and rear)

Sticky Shock A. Linkage not maintained B. Swingarm bearings not maintained C. Shock eyelet bearings not lubed D. Floating brake rod or backing place not lubed­

common on vintage bikes wich floati ng rear brake E. Missing or improper bearing spacers F. Bene shock shaft-usually caused by mounting

bo lt or clevis installed backwards Blown Shock Bladder A. Oil leak-shaft sea l blown- caused by nicked or

pitted shaft, hard-chrome worn through, o ld or worn-ou t sea l

B. Improperly rebuil t shock recencly finished wich way too liccle oil

105

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Rear 6: Rear squats

Rear 7: Rear not tracking

TESTING PROCEDURE

rear feels vague, loose, wanders

Because of rhe number of va riables involved in suspension

setup and the unique preferences o f each rider, there is no

o ne perfect setup for everyone. This is part of why resting is

so critica l. I f you fo llow rhis procedure exactly and always use

the resting log sheet in the appendix, you can make significant

improvemen ts in your bike's suspension.

Use this p rocedure o n both practice and race days.

T he more detailed you are, the easier it will be to predict

futu re needs when you switch locales. Remember that proper

suspensio n setup is best ach ieved with a grea t rider/tuner

team. The be tter you r rapport and communicatio n , the more

effective you will be. If you are in the unfo rtunate si tuation

o f havi ng to be both rider and tuner, go thro ugh the same

process and do your bes t to keep an open mind .

Here is a key question: when making a change does the

r ider feel the cha nge o r the percentage change? In other words

if yo u make a .5 kg/mm spring rate change is that a lo t or a

little? T he correct answer to this questio n is viral for proper

suspensio n tuning whether it is spring, damping, or fo r that

matter, friction. The answer is the rider feels the percentage

change, no t the change itself. If the original spring rate was

5 kg/mm then a .5 change would be 10 percent- this is

no ticeable. If the o riginal sp ring rate was l 5 kg/ mm a .5 change

would o nly be about a 3 percent change, which may not be

no ticeable at all. Studies have shown that the smallest change

most humans can feel is I 0 percent. I have found that some

riders can feel as small as a 5 percen t change. T he po int is yo u

need to make a big eno ugh c hange fo r riders to be able to tell.

Too small a percentage change is worthless and confusing.

106

There is an o ld rule o f thumb that says that with proper

setup you should bottom o nce a lap. I disagree st rongly. Let's

say your bike is set up perfectly fo r your local mo tocross

track and now you go to a no ther track that's significantly

smoother. T he rule would have you softening the suspension

to the poin t o f being mushy, perhaps even uncontro llable,

wi th big pitch changes fo re and aft . On the other hand some

riders prefer a setup where the rear bottoms gently somewhat

regu larly-5 to 10 times a lap. T he key word here is gently.

Normally I like to give the rider some cushion and not let it

go metal to metal ever.

As far as road raci ng is concerned, it is quite commo n to

use up most of the fork travel du ring b raki ng, bur I suggest

yo u sho uld never bo ttom o ur metal to metal and never

remove the bottom-our d evice. If you do there is no room fo r

error, with the possibility oflosing the fron t end. T he rear, o n

the other hand, barely moves in relatio nship to the fro nt. A

properly set up rear end wi ll no t co m e close to using all the

travel o n most tracks.

1. Before leaving for the track, record the initial settings

o n the resting log.

2. Starr wirh spring rares from rhe Race Tech website's

product o r Digital Valving Search. C heck and set sraric

sag, free sag, and check your sriction zone. Remove

excess frictio n before doing any testing.

3. On the way to the track, or befo re , if possible, go over

the testing procedure with the rider.

4. Ir is often helpfu l to use last year's bike

fo r comparison.

5. O nce at the t rack have the rider do at least two 10-minu te wa rm-up sessions without caring about suspension action. H ave fun and get loose.

6. For d irt riding wait un til the track is worth y of testing. If the track is no t very rough, it doesn't make sense to test. If the rider wan ts to ride while the t rack is still smooth that's O K, just do n't make any suspension decisions.

7. O nce the track is ready ask the rider to do two or three laps, focusing on using the exact same lines every time and concentrati ng o n the suspension action. Instruct the rider to ride cautiously, at 90 percent, not 100 percent. (Road racers should use tire warmers.)

8. Record the rider's initial feed back about what the bike is do ing on the testing log. Ask him to decide which end o f the bike is worse and start wo rking on that end .

9. Make one change at a time. T his a universal testing ru le that most tuners know-and most tuners break.

10 . Do not tell the rider what changes you are making. If you do, you can rest assured that it will affect the results.

11. Make big external changes firs t. Try to bracket the problem with external adj usters, but bear in mind that some adjusters do n't make much d ifference (particularly most original eq uipment shock compression adjusters).

12. Record all changes and com ments on the testing log in

che appendix. You do noc have co record all che settings at this point, just the changes. Lap times can be helpfu l for fine tu ning, but do not rely on lap times, as too many factors affect them, including traffic and track cond itions. Both MX and road race tracks can change dramatically du ring the day, including wind cond itions a nd track tem peratu re. Be aware of rider's energy level.

13. Have the rider test for two to three laps with each

change, and no more. Any longer than this and the rider will start to make things up.

14. Watch the bi ke on the track, taking note of the relative movement of the wheel and the chassis. T he wheel

should move up a nd dow n fa irly qu ickly and the chassis should stay fa irly even. You may take the side panels off

on dirt bikes to see suspension action better. On d irt bi kes look for excessive roost: lots of roost can eq ua l a lack of traction. Listen to the engine particularly as the rider goes over bumps. A more even rpm usually means less deflection.

15. W hen the rider comes in , ask, "H ow was it?" Let him know it might be better in one area and worse in another. Let him know the change might not be big enough to tell. Avoid "leading questions" that might p rompt an inaccurate response.

16. If you would li ke to use a checklist to prompt the rider, yo u can use so mething like th is fo r d irt : H ow was it on : • Bottoming? • Square-edge bumps? • Plushness? • Traction? • Tracking straight? • Feeling of control?

17. Get feedback on the symptoms, not the cause. If the rider tells you what it is do ing and then tells you the cause, politely ask him why he thinks it needs that change. W hat is it doi ng? W here?

18. If the rider couldn't tell, go back to the previous setting. (Sometimes the problem is very obvious when you go back to the previous set ting.)

19. Do you r best co figure out the shaft velocity a t which the prob lem occurs. Is it h igh-speed or low-speed? When maki ng valving changes, change that part of the damping curve. (A ShockClock o r other data acquisition system can be helpful here .)

20. Double check the rider's feedback by using an earlier setting to see if the feedback is consistent. Don't tell the

rider what you are doing. 2 1. O n the last test of the day, use the o riginal settings

(from the beginning of the day) co double check you r work. This one takes cou rage.

Note: Take everything with a grain of salt. Don't believe your eyes or your ears. Be willing to be wrong. Have fan!

107

Chapter 7 Tools and Equipment for Suspension Service T here is an o ld saying: the tools make rhe mechanic.

Whi le rh is is nor entirely co rrect, there is something to this concept. W ithou t the proper tools, equipment, workspace, and so on, even rhe best suspension technicians will be limited in rhe quality and swiftness of their wo rk. Using rhe proper tools is essential to success for suspension jobs, ensuring rhar rhe job gets done correctly and without any undue damage ro rhe motorcycle or compo nen ts being serviced. If you plan on being a professional suspension

This K&L scissor jack (shown with optional post adapters) is useful for heavier, flat bottom vehicles like ATVs and many street bikes.

This front stand lifts the bike by the steering stem, allowing the forks to be serviced.

108

service technician or tu ner, having rhe proper too ls will be

critical for profirab iliry. The starring point is your workspace, whether it is your

garage floor, a trailer/ truck for mobile operations, or a fu ll-o n workshop. You wi ll need a well-lit, properly-ventilated, clean area with a floor rhar can support fu ll-size motorcycles and/ or ATVs on stands or lifts with room left over ro store units in progress. No matter what you do, there will be occasions when you will be waiting on parts.

Ser up your work area wirh shelving to store parts, jobs in progress, and so fo rth. You will need cabinets for chem ical storage, an oil d isposa l drum, parts washing machine, a ir compressor/air lines, dri ll press, and, of course, a sturdy work bench built ro rhe correct height fo r you to work comfortably. As you will be working with oil and chemicals, a metal or lam ina re bench top is strongly recommended .

These icems can be sourced locally from hardware and tool stores fo r the most pare. You can also build or purchase large pieces such as benches, cabinets, and so on based upo n your budget, needs, and the level of professionalism you w ish to convey.

Now that your work area is prepared , you will need to d isassemble some vehicles. Street and dirt motorcycles will require special stands; ATVs are a li ttle easier to deal with as they are more stable. If you will be working primarily on ATVs, you don't need much in the way of special stands. If, however,

This hydraulic lift is a bit quicker and more stable than the scissor jack shown, but it takes up a little more floor space.

you would like to be ab le to have both fron t and rear shocks o ff the uni t at once, some sort of a stand will be required.

Di rt bikes are relatively easy to work with as they are fai rly lightwe ight. T here are a variety of stands on the market that work well , or you could build something basic on your own fai rly easily. Make su re your dirt bike stand wi ll carry the bike high enough and well-balanced enough to remove the front and rear suspension simultaneously.

Street bikes are a little mo re challenging. T hey are heavier and often have easily d amaged painted body panels in the way. A front wheel chock such as the Condor Pit Stop from Lee Parks Design is indispensable fo r setting sag as well as fo r steadying the bike while working o n it. Supporting the rea r end is fa irly straightforward , wi th a num ber of op tions such as stands from Pit Bu ll, K&L, and ochers. A cen ter jack can be used in conju nction to raise the front end- the K&L MC450 is the industry standard . A n option fo r lifting only the fro nt end for fo rk removal is a front end stand.

O u r favorite stand fo r suspension service is the K&L MC360 li fe, which hangs the bike with both wheels off the ground for front and rear service and allows the bike co be

This Park Tool Vise was originally made for working on bicycles but can be used on forks as well. A bench-mount base is available for a bit more stability.

moved around on wheels even when it is half taken apart. Sport and touring bike owners tend to be very concerned about scratches and other d amage-one dropped D ucati or Gold Wing can burn up the profits of severa l suspension jobs, not to mention the cost in customer relations. Using quality equipment will help keep the bike upright, off the floor, and easy to work on, as well as conveying a high level of professionalism .

Now that you have removed the suspension components from the bike, it's time to get to wo rk improving their performance. Good quali ty basic hand cools such as sockets, wrenches, and screwdrivers are of cou rse required. Cheap im ported cools can rou nd off or leave ugly marks on fas teners that many owners sim ply won't tolerate. Six-poin t sockets and wrenches will help ensure easy removal without broken cools-it can take surprising effort to crack loose a facrory­installed fastener the flrst time. (And don't fo rget that torque wrench fo r reassembly.)

H igher quali ty ratchets will have flner ratcheting ac tion, making it easier to work in right places. Anodized fo rk caps made of soft aluminum may require large, special wrenches with un ique sizes or shapes to remove chem without damage, like chose in the Race Tech TFCW line. A specia l spring compressor (such as the TFSC series) may be required fo r street bike forks, and almost always for shock absorbers (TSSC series). T hese are very critical tools: damage fro m flying

components- or, worse yer, personal injury- can resulr from improper spring removal or insrallation. Like our moms used to say, "Ir's all fun and games until someone loses an eye!"

You will want a quality bench vise to hold components and special vise jaws designed for suspension work. Race Tech TMVJ 065 vise jaws flr directly into Craftsman, brand vises (and others). T hey are aluminum and have a V-cut that holds

rounded components securely, plus they include special pins to facilitate T FSH shaft holding tools. W hen worki ng with

suspension compo nents, you are constantly holdi ng, loosening, or tightening various shafts, fro m fork cartridges to shock shafts-holding chem securely without damage is essential.

Never use vise grips on a suspension shaft , damping rod , or similar, as they will create damage that ruins seals and

bushings. This can result in lost damping and fluid leaks, not to mention expensive component replacement. T here are also freestanding and bench-mounted stands that wi ll ho ld

a fork or shock from Park Tool. T hese stands can be used as a workstation, as they allow the compo nents to be ro tated, inverted , and so o n while they are clamped in the holde r. These uni ts are not as sturdy as a bench vise, bu t they are a bit more versatile.

T he cartridge forks found on many stree t bikes, mini bikes, and o lder MX models may require a TFCH -series cartridge holding tool. This tool keeps the cartridge from sp inning during disassembly and reassembly. T his style of fo rk may also need a TFBT-series bleeding tool for bleeding the cartridge upon assembly. T he tool attaches to the rebound

109

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Nitrogen hose: This high-pressure hose worl<s between the TSNR 01 Nitrogen Regulator and TSNG 02 Nitrogen Gauge. Finger-tight fittings are quick and easy.

A shock nitrogen charging tool easily reaches hard-to-get-to recessed valve stems without an extension. Valve core plunger is located on the top for easy use.

rod so rhar ir can be srroked rhrough irs en tire rravel ro purge a ll rhe air from rhe carrridge. Ir also aids in spring insrallarion by allowing rhe rebou nd rod robe pulled our pasr rhe spring ro be rearrached ro rhe fork cap.

Mosr fo rks should have rhe fork oil ser by level rarher rhan volume for accu racy. Remember rhar fo rk oil level sers

rhe air space in rhe fo rk (rhe secondary spring effecr), and is an excellent runing variable. T he TFOL 02 Fork O il Tool is

in a class by irself. T here are orher models on rhe marker char are less expensive, bur rhey seem ro requ ire rhree hands ro opera re. Twin-chamber fo rks requi re rhe use of a G raduated Cylinder (TFGC 500) ro measure rhe volume as rhere is no practical way ro use a Fork O il Level Tool. Of course, you musr have an assorrment of fo rk seal drivers like rhose in rhe TFSD series. A good seal driver will be of a splir design, so ir will work on inverred forks. Ir should also be hefry in order ro drive rhe seal properly, and concentric ro ensure an accu rare fir ar rhe seal and into rhe seal caviry.

Parr cleaning is a critical parr of suspensio n work. In rhe o ld days solvent was rhe way ro go, bur roday wirh new laws ro prorecr borh us and rhe enviro nment, and new techno logy, rhings have changed. U lrrasonic wash srarions are rop of rhe line. They do an amazing job on some nasry parrs. T here are a lso "vaporless" parrs washers rhar clean rhemselves wirh a

110

A nitrogen regulator provides output pressure to 300 psi.

Series Seal drivers: Split design for both conventional and upside-down forl<s.

Pro oil level tool: Collapsible lube to set oil level. Easy, two-handed use!

push of a burron over nighr. H or soapy warer-b lasr cabinets do a grear job on muddy parrs as well. Safery-Kleen has a fu ll assorrmenr for your selecrion.

Shock service will require a nitrogen charging srario n consisring of a nitrogen horde (ava ilab le from your local

welding supply house) equipped wirh a regu laror such as rhe TSNR 01, T SNH 48 hose, TSNG 02 gauge, and a TSNN 0 1 needle. If you plan o n servicing KTM products wirh WP Suspension, a TSNC 02 charging rool will save you hundreds over rhe OEM rool.

Nitrogen needle: Designed for gas-charged shocks with se~-sealing-type rubber valves.

A WP n~rogen charging tool clamps onto the reservoir of all WP shocks with a reservoir.

Ocher shock-servicing muses are a reservoir cap puller such as rhe TSCT 01. T his rool wi ll pull our rhe reservoir cap wirhou r damaging rhe un ir or abusing you r fingers. Shock sea l head circlip removal frusrrar ion can be avoided

wi rh a TSCP 0 I clip cool. Insra lling sea l heads can be a headache as rhey wanr ro cock sideways-the TSSS series

makes rhis rask much easier by qu ickly and evenly driving in rhe sea l head.

If you w ill be servicing KTM/WP-brand shocks, a

TSPS-series needle pin rool is needed ro exrracr and replace rhe metering pin and/or relescopic need le. Some brands of shocks have a dusr cap rhar is rhreaded­

rhese w ill require TMPS-series pin spanners in order ro remove rhe cap wirhour damaging it. Ohlins shocks and forks will require myriad special cools char va ry wirh rhe ap plication. Ohlins cools are ava ilab le through select O hli ns distrib urors.

Afrer you have completed your suspensio n work, it will be necessary co dial in rhe preload, ser rhe sag, and adjusr the clickers. A Race Tech Sag Masrer TSSM 0 I will make sho re work of sag setting and the TSPA 0 I Shock Preload Adjusting Tool will aid in reaching preload collars. For adjusting clickers buried underneath handlebars, rhe TFCA 01 is inva luab le.

A reservoir cap removal tool screws onto the Schrader valve to facilitate removal of the bladder cap.

A shock clip tool removes shock retaining clips.

Series Seal head selling tool: allows easy removal and installation of most shock seal head assemblies.

Don'r forger to record all you r settings. Provide a copy of rhese setrings co your cuscomer while saving one for you r records co refer co later as needed.

If you are going co be testing on a regular basis, you may wish co consider investing in the ShockClock. It will provide you wi th data, details, and information rhar even rhe besr resr rider cannot convey, in addition co quanrifying or disputing rhe rider's feedback. It is one of the mosr efficient, affo rdable data acquisi tion cools availab le.

This overview will get you started by providing rhe essentials needed. T he re are many more cools you may need

111

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o r want to own as rime goes on based on your business as wel l as the types of jobs you encounter. You can never have too many tools, only too few! Build your toolbox as your budget, work, and needs dictate. Take care o f your tools by keeping them organized, clean, away from hammers as much as possible, and especia lly away from friends who want ro borrow and nor return them.

See rhe com plete listing of suspension tools at racerech.com and refer back to this chapter as you go through rhe service department section of rhe book. T he beginning of each process includes a list of the tools needed ro complete each job.

Pin Spanners have a unique design with a reverse taper on the hardened pins. This helps them dig in so that they don't pop out during use.

Sag Master: Used to measure static "race" sag. Sag is read directly-no more subtracting!

T Series Shock metering needle pin spanners can be used to remove the

compression needle from the shock body on KTM WP PDS shocks.

This fork spring compressor for road bikes can be used in the field as well as in the shop.

A shock preload adjusting tool can be used aggressively on preload adjusting collars without damaging them.

112

Chapter 8 Suspension Service Department TOOLS, TIME, AND SKILL REQUIREMENTS Suspensio n service jo bs vary in their degree of difficulty

as we ll as t heir tool a nd skill requ irements . Specia l too ls

will be needed often , so you will want to be p repared ahead o f time-this wi ll ensure yo u don't have to stop

in t he middle of yo ur work to fi nd these item s. Always

have access to a quality service m anua l for procedu res,

wear specifications, torque values, and details specific to

the model you are wo rking o n. This section is designed

to be a genera l guide fo r each major type of suspension

system used on today's (and yesterday's) motorcycles,

but it canno t cover t he nuances of each specific fo rk and shock ever made.

T he photos included with each how-to project will help

you to be p repared and know in general what to expect as

you begin the service/installation job. Time and difficu lty

will vary based upon rhe model of motorcycle combined with

your personal mechanical apti tude- the ratings provided are

intended only as a guideline. Remember chat quality coo ls

make a significant difference, so do n't skimp, as it cou ld

cost you in the lo ng run. Special tool requirements are to be

expected, so p lan ahead. If you are going to be removing and

replacing suspension componen ts fro m the bike, make sure

you have the appropriate stands to support the bike while

you work.

You will also need expendables such as spray chemicals

and proper waste oil storage and d isposal capab ili ty. Always

wear safety glasses and have a first aid kit readily availab le. Be

mindful of the environment while you are working.

Skill Levels (indicated by number of wrenches) • # 1 Basic: Minimal special skills or cools required. A

service manual fo r the bike, this book, and product

installation instructions will be needed , combined with

basic mechanical skills and background.

• #2 Intermediate: Some special skills and cools wi ll be

requi red. A service manual fo r the bike, this book, and

p roduct installation instructions will be needed. You

will also need to be comfortable working with new or

unfamiliar procedures withou t intimidation. Assistance

may be required on your first attempt.

• #3 Advanced: Specia l skills, procedures, and cools will be

required. Training and/or assistance from an experienced

individual is recommended on at least rhe fi rst attempt.

There is greater po tential for personal injury, so use

caution when working.

Time Commitments • A Level: Minimal time required: 2 to 3 hours with

experience, 3 co 6 ho urs first attempt.

• B Level: Moderate ri me required: 4 to 5 hours with

experience, 5 to 8 hours firs t attempt.

• C Level: Major rime required : 5 ro 6 ho urs with

experience, 6 to 9 hours first attempt.

Tools Basic hand cools; digital calipers , tape measure , 8- l 9 mm combination wrenches, 6- I 4mm !I.I'' drive sockers/raccher,

I 0-19 mm Ya" drive sockers/raccher, 22/24/27 mm Yi" d rive

sockets/ ratchet, 4- I Omm Allen sockets, long 6/8/!0mm

AJlen sockets, 17I 19122124 combina tion Allen socket, small/

medium/large straight sloe screwdrivers, #2/3 Phillips-head

screwdrivers, pliers, snap ring pliers, side cutters, fi le, hammer,

punch, impact wrench, tubing cutter

Special Tools See Tools Section of each project introduction for details.

Equipment Bike stands/jacks, e tc . (see tools section for details)

Expendables Spray solvent (brake/contact cleaner, e tc) , spray o il (WD-40,

Bel Ray 6-1, o r similar), grease, suspensio n o ils in assorted

viscosities, ch read locker (high strength Loctite), spray polish,

sho p towels, sandpaper assortment (280-400 gr it), place g lass,

sho p roll (500 grit), steel wool, Scotchbrite pads, waste oi l/

chemical storage.

113

PROJECT 1 Damping Rod Forks

0 Skill Level: '

, "t~ Time: A ···-~

fj Tools: Basic Tools, Fork Seal Driver (TFSD series), Oil Level Setting Tool (TFOL 02), Damping Rod Holder Tool (OEM), Bike Stand/Jack

Dam ping rod fo rks are used on lace model as well as vintage screec and dirt bikes. This is the simplest fo rk design, requiring a minimum of special tools and skills. Damper rod forks a re conventional sryle (shiny cube on top), are easy to work on,

and can be improved dramatically with Gold Valve Camidge Emulators. Generally the biggest challenge with th is sryle of fork can be re moving the botto m bole-an impact wrench is a muse. Some models will require snap ring pliers co remove the seal

retaining circlip, and vintage models may require some damping rod machining when Emu lators are installed. Service Tip: If the bottom bolt spins around but won't come out, try puffing the chrome tube out hard while running the impact

wrench. You can also try putting the fork main spring back in and pushing against the chrome tube, otherwise you will have to obtain a damping rod holding tool or make one yourself.

Disassembly

Clamp the fork tube in a vise with soft jaws specifically designed to hold fork tubes. Loosen the cap with a socket and ratchet, making sure to press down during the last few threads to prevent stripping or uncontrolled release. Note: some models like Honda Gls have extreme amounts of preload, which can be dangerous released without control.

114

If the foril cap is stuck, ~ is often helpful to shock the thread. Hammer on the foril cap with a properly sized socket lo help break the thread loose. If you use this method, be aware you can damage both the socket as well as marring the cap. Make certain you are wearing safely glasses before considering this option. In many cases you can put a few sheets of paper or a rag between the socket and the cap to protect ~. Note: the socket doesn't have to fit the hex.

To measure the amount of preload on damping rod forils, rest the foril cap on the end of the spacer or spring and measure from the lop of the foril tube lo the sealing lip (the surface that would contact the foril tube when lightened) on the cap. This is a direct measurement of preload unless the thread on the cap is hilling the thread on the foril lube.

Remove the parts from the foril lube. In this case we remove a washer, spacer, another washer, and the foril spring.

115

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116

Remove the seal dip with a dip tool or small screwdriver.

Loosen the compression bolt with an impact driver while pulling on the upper Jori< leg to keep it from spinning. H ii continues to spin, you can reinstall the Jori< spring, spacer, and cap, then compress the fork. tt it still continues to spin, you may have to make a holding tool for the damping rod.

H the compression bolt is stuck, hammer on the compression bolt with a property sized socket to help break the thread loose. Again, ij you do this be aware you can damage both the socket and the bolt. Wear safety glasses.

Remove the compression bolt.

Pour out the fluid and dispose of ~ properly.

Slide hammer out the fork seals and bushings by vigorously extending the fork tube. Make sure the fork slider is firmly clamped in the vise. Make sure it is clamped on a strong area of the leg.

117

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118

Remove the damping rod and top-out spring by inverting the fork tube.

Remove the bottom-out cone from the slider. It is located on the damping rod, so it may be in the bottom of the fork tube.

Remove the outer bushing and seals from the tube.

Remove the inner bushing from the fork tube by spreading the bushing with your thumbnails. It may be easier to spread the bushing with a thin-blade screwdriver, but be careful not to damage it.

Inspect the Teflon bushing surfaces for embedded material and wear as well as possible damage done during disassembly. ~the bushings have worn-out Teflon, check the lower fork leg for dents as these are the main cause of this kind of wear. ~ there are dents, the lubes may be able to be repaired by a competent professional. otherwise the fork slider will need to be replaced. If there is embedded material, find the source before continuing. Inset: Here is an example of a new bushing next to an extremely worn-out bushing.

Inspect the fork tubes for pits. Minor pits can be polished out with 500-grit sandpaper. Major dings require tube replacement.

119

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Reassembly

120

H you are installing Race Tech Gold Valve Cartridge Emulators, drill out the damping rod compression holes as described in your specific instruction sheet. Notice drilled damping rod next to the stock one on the right. Be sure lo chamfer and deburr the holes.

Install a new inner bushing.

Install the lop-out spring on the damper rod and insert the rod in the fork lube.

Install the bottoming cone onto the damper rod.

Install the inner fork tube into the outer fork tube.

Tighten the damping rod bold to the manufacturer's specs. ~the damping rod spins, install the spring and cap and compress the spring. ~this doesn't work, you might have to use or even make a damping rod holding tool.

121

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122

Install the outer bushing and seal washer with a seal driver.

Grease the seal. Normally we recommend seal replacement whenever the forb are serviced.

Slide the seal on the fork tube using a comer of a heavy gauge plastic bag (see inset) to protect the seal from being damaged by the end of the fork tube. Pull the bag taught to ease installation.

Install the seal into the slider with a seal driver.

Install the dust seal with the seal driver. On some models, the retaining clip goes on before the dust seal.

Install the seal clip.

123

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124

Drop in the Gold Valve Cartridge Emulator. Notice different types of Emulators on the left that cover a wide range of fork types and diameters. Check to make sure the Emulator is seated property and in the proper direction. Many of the Emulator adapters for vintage models have a piston ring built into them to dramatically improve sealing and performance.

Drop in the spring, washer, spacer, and washer. Set the cap on the washer.

Check the preload by measuring the distance from the lop of the fork tube to the sealing lip on the cap. The sealing lip is the portion of the cap that will contact the lop of the tube when the cap is lightened. In this example we measure 38mm of preload w~h the existing spacer length. For this particular bike and rider we need 1 Omm, so we will shorten the existing spacer 28mm.

Cut the spacer to provide the correct preload. Make sure the spacer is cut squarely and deburred. tt an Emulator is installed, this will procedure will compensate for its height Inset: Re-measure the preload lo check your work

Remove the spring and spacers. Pour in the fluid.

Bleed the fork by stroking the tube. Make sure there is an excess amount of fluid in the fork.

125

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126

Adjust the lube extension on the oil sucker tool lo equal the dimension of the target oil level.

H you are using an Emulator, install it before selling the oil level. Collapse the tori< all the way and suck out the excess oil.

Install the tori< cap and use a torque wrench to tighten it to manufacturer's specs.

PROJECT 2 Standard Cartridge Forks with Gold Valve Installation

0 Skill Level: ' '

Time: B

~ Tools: Basic Tools, Fork Cap Socket (TFCW Series), t.J Fork Spring Compressor (TFSC Series)

for street bikes, Cartridge Holding Tool (TFCH Series), Fork Seal Bag (TFSB), Shaft Holding Tools if Revalving (TFSH Series), Fork Seal Driver (TFSD Series), Cartridge Bleed Tools (TFBT Series), Oil Level Setting Tool (TFOL 02), Bike Stand/Jack

Standard cartridge fo rks are fo und on most lace model sporcbikes, some cruisers and tou rers, mini MX bikes, and posc­vincage MX bikes from the lace 1980s co lace 1990s. T h ese can be conventional or inverted (shiny cube o n bottom).

T his sophisticated fork design requi res some special cools co work on. Care must be taken during service co avoid damage to expensive internal components and co ensure proper operation when com pleted. Mose sporcbikes have substantial installed spring preload, so be careful of sharp spring spacers under pressure so chat you do not inj ure your hands or fi ngers! Use a fork spring compressor on chose models for ease and safery.

Service Tip: Inverted-style forks require that the seals cross over sharp edges at the bushing grooves on the fork tube, which can easily

rttin a new seal. Use a heavy gauge ( 4mm) plastic bag over the sharp edges or a thin piece of plastic wrapped inside the seals as you slide

them over the groove. And always grease the seal lips.'

Disassembly Back off the rebound adjuster with a screwdriver.

127

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128

Hammer on the fork cap with a property sized socket to help break the threads loose. This is not required but is quite effective for stubborn fork caps.

Remove the cap. On right-side-up forks keep significant downward force to control the cap in case it has an external top-out spring with lots of preload. Big touring and sport touring bikes typically have this issue. (Be sure to whistle while you work.)

Clamp the fork spring compressor in a vise. Mount the fork in the fork spring compressor. Screw the thumb screw into the holes in the spacer.

Compress the fork spring by tightening the compressor. Stop tightening when the tool hns the top of the tube or earlier ~you have dearance or you will start destroying things.

Insert the holding tool. You may have to pull up on the cap to get the tool in.

Break the jam nut loose while holding the in place wnh a second wrench.

129

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130

Remove the forl< cap.

Thread on the bleeding tool, pull up, and remove the clip.

Release the preload.

Remove the forl< spring compressor.

Remove the bleeding tool, washer, spring spacer, and forl< spring.

Dump out the old oil.

131

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132

Remove the cartridge Allen bolt while pulling on the cartridge. Inset: H holding the cartridge by hand doesn't work, use the Race Tech Cartridge Holding Tool.

Remove the cartridge.

Remove the upper tori< leg. The model shown has two outer bushings and slides off easily. Most models (particularly before 2003) have an inner bushing on the inner fork tube and must be "slide-hammered" off. If the outer fork tube does not slide off easily, remove the dust seal and clip then slide-hammer it apart. There are some models that are notorious for coming apart wijh difficulty. It is often helpful to heat the seal/bushing area wijh a heat gun before slide-hammering it apart.

Inspect the inner lube for ptts or imperfections.

Remove the dust seal on the upper fork leg wtth a wood chisel.

Remove the seal dip.

133

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134

On this style of fork with two outer bushings, the seal remains in the outer tube and must be pried out. Remove the seal and washer by prying it out with a wide tool to spread out the load. Be very careful not to damage the fork tube. You may need to pad the edge with a folded-up rag.

Remove the rebound adjusting rod from the cartridge.

Clamp the cartridge assembly in the shaft holding tool and unscrew the compression base valve. Some models are held in with a clip. In this case push the base valve in far enough to expose the clip and remove it with a clip tool. Then remove the compression assembly.

tt the compression valve is stuck, heal the end of the cartridge al the compression valve w~h the propane torch or gently shock the threads w~h a hammer by lapping on the outside of cartridge at threads. tt you lap on the thread be sure to hold the cartridge lube flat on the anvil surface of the vise. H~ the hammer squarely so as not to dent the tube. Only h~ the cartridge tube on the very end where the thread is.

Clamp the compression base valve in a vise w~ soft jaws. On models that have the end of the valving shaft peened, fi le the end of the compression shaft down lo the surface of the nut.

Remove the compression nul

135

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136

Remove the compression valving stack from the holder using a welding rod or a heavy wire. Notice this •special tool" has a hook so that the valving stack is captive for deaning.

Clean the valving stack with contact deaner .

Clean the center of the valving bolt with compressed air to remove filings and other debris .

Clean out any debris in the stacking and on the shaft.

Chamfer/deburr the end of the cartridge bolt shaft slightly.

Finish both piston faces by sanding on 600-grit sandpaper over a plate glass base for a smooth and flat surface. Caution: sometimes the valving pistons are not intended to be flat all the way across. Refer to the valving section for preloaded piston types. On this type, do not surface the preloaded side of the piston.

137

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138

H you are installing a Gold Valve, follow the instructions with the kit. Install the new valving stack and use Loctite on the piston assembly nut (inset). Make sure the check valve is free before tightening the nul

Check for compression check-plate freedom!

Torque the compression valving stack.

Heal the seal head to aid disassembly ff needed.

Or with a hammer, tap the seal head threads lo help jar them loose. Sometimes the thread is "staked", in other words there are punch marks in the threaded area to insure they don't come apart. H this is the case, drill out the punch marks but only to the depth of the outer lube. Do not drill all the way through the seal head.

To access the rebound valving on models with peened-on bottom-out pistons, remove the cartridge seal head. To support the cartridge so that it won't crush in the shaft holding tool, temporarily reinstall the compression base valve in the cartridge. Clamp the cartridge tube at the compression valve assembly in the shaft holding tool. Next, using the cartridge holding tool, unscrew the cartridge seal head assembly. H ii is stuck, use heat or tap the thread. Note: Many models do not have a peened-on bottom-out piston. On this type you can simply slide out the damping rod assembly without having to remove the seal head.

139

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File the peening on the rebound valve.

Remove the rebound nut.

140

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Reassembly

142

Surface the base plate to make sure ~·s flat. Again, use sandpaper on a plate glass surface. Use 280-320-grit for this steel base plate.

Surface the rebound piston next.

Follow the instructions for the Rebound Gold Valve if you are installing one. Install the rebound assembly.

144

Make sure the thread is clean and Loctite the rebound cartridge seal head.

Insert the rod into the cartridge.

Tighten the seal head.

Use a small drop of Loctne on the thread (if n is the threaded type). Install the compression base valve assembly into the cartridge.

T ighlen the compression valve assembly.

Temporarily install the preload spacer and fork cap. Back out the preload adjuster all the way and measure relaxed set length. Refer lo the spring preload section in Chapter 2- Springs

145

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146

Measure the free length of the spring. Calculate the relaxed preload by subtracting the relaxed set length from the free length of the spring.

Optionally on this model you can line up one end of the spring with the spring seat and measure the relaxed spring preload directly as shown. Cul the preload spacer to set the proper preload. See setting preload section in the Springs Chapter .

Grease the fork seal.

Install the wiper and seal onto the lube. Use a 4mil thick plastic bag on the end of the tube to protect the seal. On models with an inner forll bushing groove pull the bag taut to aid in protection.

Install the seal washer and ciip.

Slide the outer tube over the inner tube.

147

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148

Install the seal by driving it with a seal driver.

Install the seal clip and then seat the seal clip with a screwdriver.

Install the wiper with the seal driver.

150

Torque the compression bolt to manufacturer's specs. H the cartridge spins, use a TFCH-Series cartridge holding tool (inset).

Add the proper suspension fluid.

Tip: You can prime and speed up bleeding the cartridge by putting your hand over the top of the tube at full extension, then compressing the fork. The pressure will force oil into the cartridge. Then stroke the damping rod until the cartridge is bled.

There are two types of forks: those with and without a bleed hole in the inner tube. This hole equalizes the oil level in the area between the inner and outer tube. Forks without this hole must be extended all the way to evacuate this area before setting the oil level. It's good to notice which type you have before assembly.

Drop in the rebound adjusting rod. Collapse the outer fork tube. Set the oil level by sucking out extra oil wtth the TFOL oil level tool.

Collapse the outer fork tube. Set the oil level by sucking out extra oil wtth the TFOL oil level tool.

Add the spring, spacer, and spacer washer. Screw the proper TFBT bleeding tool onto the damping rod thread.

151

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152

Clamp the tori< spring compressor in a vise. Put the fork assembly into tt. Gently tighten the thumb screw into the hole in the spacer. Compress the spring with the compressor enough to allow inserting the cup tool. Note: You may have to pull up slightly on the damping rod to get the cup in. Do not use an impact on the spring compressor and be sure to stop tightening when it is fully compressed.

Set the adjuster screw. There are three types. The first two are the most common on street bikes. On these two types the cap must be screwed on the proper amount. One style has an adjuster screw that will stop as tt is screwed in and the other will keep going and eventually fall out- along with the tiny detent ball and spring. Identify which type you have-first unscrew the adjuster all the way. ~ you screw tt in more than seven turns (28 clicks) and tt hasn't stopped you probably have the kind that comes apart. If this is the case, stop, back out the screw all the way, and screw tt in four turns (20 clicks). On the type that stops, screw tt in until it stops and back ~ out 2 clicks. Most dirt bikes (and a few street bikes) are the third type. This type is made so all you need to do is back out the rebound adjuster all the way and screw the cap on until it stops.

Use Loctite on the damping rod thread.

Screw down the cap on the damping rod until ~ is just snug. On the first two types, the rebound needle is now touching the seat. Tighten the jam nut up against the cap w~ your fingers. Hold the cap so that ~ doesn't tum. Now back out the adjuster screw 'h tum so that ~ is no longer seated.

Tighten the jam nut to manufacturer's specs.

Tighten the fork cap. The torque on the cap is usually very low (around 10 lbs-ft. or 14 Nm). Consutt manufacturer's specs.

153

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Precisely align the sticker.

Make another goofy pose when someone has a camera. (Notice the form though.)

155

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PROJECT 3 Twin-Chamber Forks

0 Skill Level: ' ' '

Time: C

~ Tools: Basic Tools, Fork Cap Wrench (TFCW) W Twin Champer Tool (TFCT Series), Damper

Rod Holder (TFHP), Fork Seal Bag (TFSB), Shaft Holding Tools if Re-valving (TFSH Series), Fork Seal Driver (TFSD Series), Graduated Cylinder (TFGC), Nitrogen Station for Bladder Forks (see tools section), Bike Stand/Jack

T win-chamber forks are used on late model MX bikes. No t always an inverted design , these fo rks may also have nitrogen bladders instead of pressure springs. T hey require some special too ls and procedures. G reat care must be taken on some

models because o f the sharp edges and threads at the base o f the damping rod cha t can damage car tridge seals, resulting in lost damping.

Service Tip: When replacing only the fork seals (no re-valving), the inner chamber does not need to be disturbed or drained. Jfyou do so, check far a foll cartridge with the cartridge out of the fork, push the damping rod in, and watch to see that it re-extends folly on

its own. Also make sure that no fluid leaks out around the shaft seal. Be mindful of bushing grooves when installing fork seals.

Disassembly

156

Loosen the compression valve assembly with a fork cap wrench. It is located on the inside of the outer hex. It may require a special wrench or socket.

Loosen the tori< cap w~h the tori< cap wrench but do not remove ~ completely.

Pour out the oil and dispose of properly.

Loosen the damping rod bolt at the bottom of the fork. When damping on the for1<. bottom. select the strongest location. Never damp on brake arms or smaller tabs.

157

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158

Compress the outer tube and insert a holding clip tool on the damping rod. Our new clips are made of special plastic, so there is no chance of marring the damping rod.

Loosen the jam nut.

Remove the damping rod bolt. Tip: On Showas with a D-shaped rebound adjuster rod, hold the rebound adjuster in a fixed position with a screwdriver while you unscrew the boll. This will keep the aluminum D-shaped rod from rounding out if the adjusting screw is corroded and light.

This is a close-up of 0-shaped rod.

Remove the 0-shaped rebound adjuster rod.

Compress the fork and remove the dip tool.

159

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160

Remove the cartridge.

Inspect the cartridge for damage such as dents, wear, etc.

Check for evidence of good seals. Compress the cartridge all the way, and it should return to the fully extended position by itself. If it doesn't, the internal oil level may be low, possibly caused by leaking shaft or reservoir seals. If it is a 05 YZ, it will not return all the way as the pressure spring is too short from the factory. Also it may not extend all the way if there is only slightly too much friction.

1-z w ~ I­CC

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z 0 c;; z w Cl.. (/)

::I (/)

162

Slide hammer the fork seal and bushings out forcefully.

Tip: heal the seaVbushing area if the tubes don't come apart easily. On certain models, most notably KYB 46mm upside-down forl<s this is a good idea before slide hammering is done.

Some forks may suffer damage to the Teflon bushings during disassembly (as shown). This is common on 46mm KYBs. It's good to have extra bushings on hand.

Another way to remove the seal wnh a minimal chance of damage to the bushings is to completely fill the fork wnh used "work" oil, invert n, remove the wiper and dip, and put n into a hydraulic press to force the seal out.

Remove the inner fork bushing by opening up the bushing using your fingernails inserted into the gap. ~ the bushing is too stiff, use a screwdriver.

Remove the bushings and the seal washer.

163

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~ =: 3: m ~

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~ w Q,. en ;:) en

164

H you're not replacing seals (though it's always recommended), use boxing tape to cover the sharp edge of the bushing groove during removal.

Inspect the bushings for damage, including worn-down Teflon or embedded material.

Inspect the tori< tube for pits, dings, and straightness. Make another goofy pose that might offend a really near-sighted person.

Inspect the condition of the hard anodizing, looking for wear inside the outer fork lube with an inspection mirror and flashlight.

Gently hold the cartridge assembly in a vise and unscrew the compression assembly.

Compress the damping rod lo lilt the compression assembly.

165

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1-z "' ~ I­CC

~ "' 0

"' u > cc "' (/)

z 0 (ii z "' Cl.. (/)

:::i (/)

166

Remove the compression assembly.

Empty the oil from the cartridge.

File the peening from the lop of the compression shaft down lo the nut surface ff there is any.

Remove the compression valving nut.

Remove the compression valving assembly. It is helpful to use a welding rod bent into a special tool or a small screwdriver.

Chamfer the end of the compression valving shaft w~h a fine, flat file.

167

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-0 m z (/)

i5 z (/)

m ::J:I < c=; m c m

~ =: :!: m ~

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z 0 <n z w Cl.. (/) ::::> (/)

r; ~· t ..... ••

-!ftw '

168

.. .

' -0-

,, J\ .

1

r.-1

JI

.. L ·~

~ F1 . ' F ----'I J

t' J

., J

~

..

,,,._,,

Blow out the center of the shaft wnh compressed air to remove filings.

H you are replacing the pressure spring or reservoir piston seal, you must disassemble the reservoir. While maintaining pressure on the spring and reservoir piston, clamp the shaft holding tool on the shaft. Remove the compression valving holder by unscrewing n.

Disassemble the reservoir and pressure spring shaft. Inspect them for wear. Some models wnh aluminum shafts have severe wear problems. Inspect the seals and remove the clip. Note: The necked-down area bleeds the cartridge during assembly.

Add a small drop of red Loctrte to the compression valving holder thread.

Install the pressure spring, reservoir piston, and compression valving holder. Tighten the compression valving holder wrth a shaft holding tool. Use an adjustable wrench to apply addrtional leverage.

Wash the compression valving stack in contact cleaner.

169

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"ti m z (I)

i5 z (I) m ~ c=; m c m

~ =: 3: m ~

._ z .... :::!: ._ a: if: .... c .... ~

> a: .... (I)

z 0 (ii z .... "­(/)

::::> (I)

Surface the piston on 320-grit or finer sandpaper on a piece of plate glass.

Halfway through, showing uneven surface.

170

Before

Complete

COMPRESSION PISTON ASSEMBLY

Stock compression stack components laid out in order.

G2-R compression Gold Valve with restrictor valving stack. G2-R piston showing refill ports on the side and the recess on the

compression face for creating preload and restriction.

Race Tech G2-R Gold Valve compared to the stock piston.

171

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0 z Cl) m :io < c:; m Cl m ~ :io .... 3:: m ~

~ z w :Ii: ~

~ w c w u > a: w (/)

z 0 <n z w Cl.. (/) ::::> (/)

172

Surface the base plate.

Install the stock compression stack or the Race Tech G2-R stack.

Apply a small drop of Loct~e to the compression valving shaft nul

SETTING PROPER STACK HEIGHT

Set the proper total stack height so that the nut gets full engagement and doesn't run out of thread.

Incorrect stack height on a G2-R Correct stack height

Stock piston incorrect Stock piston correct

173

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0 z Cl) m :io < c:; m Cl m ~ :io .... 3:: m ~

1-z w ~ l­a: ~ w 0 w u > a: w (/)

z 0 <n z w Cl.. (/)

:I (/)

174

Check to make sure the check valve is free.

Torque the compression valving shaft nut. (stock/G2-R)

Continue disassembling the cartridge. Remove the damping rod jam nut.

On Showas with 12mm shafts, the trailing edge of the last thread on the damping rod is razor sharp. This edge can easily tear the shaft seal. Carefully dress ii up with a fine file.

Pack the thread with grease lo help them gel through the seal during removal from the cartridge.

Push the damping rod out through the seal.

175

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~ =: 3: m ~

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f w Cl w u > a:; w en z 0

~ w Q. en ;:) en

176

Put the rebound rod in the shaft holding tool and remove the peening by filing ~ down to the nut face.

Remove the rebound valving nut.

Remove the rebound valving assembly.

Chamfer the rebound valving shaft lightly. Use a wire wheel on the shaft end to smooth n.

Blow out the center of the shaft wijh compressed air.

Inspect the rebound rod for pns, excessive wear, bends, worn-through anodizing, and so on.

177

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-a m z (/)

i5 z (/) m :g < c=; m c m

~ =: 3: m ~

!z w :IE l­a: if w c w 0

> a: w en z 0

~ w ~ en ::I en

178

REBOUND VALVING STACK

Rebound stack exploded view.

Every valve has two distinct sides. The piston on the left is showing the recessed side. This is the mid-valve/check valve side. The piston on the right is showing the flat side, which is the rebound valving side.

----~-~--.., Surface the rebound piston on 320-grit sandpaper on a piece of plate glass.

Use a fingernail to remove any embedded material.

Clean the rebound valving stack.

179

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~ z w :Ii: ~

~ w c w u > a: w (/)

z 0 c;; z w Cl.. (/) ::::> (/)

Assembly

180

Inspect each shim for deformation.

Install the mid-valve or check valve on the valving holder. The mid-valve consists of a cupped washer, sleeve, check spring, and mid-valve stack. A check valve consists of a cupped washer, sleeve, check spring, and check plate.

Install the rebound piston with the recessed side down.

Install the rebound valving.

Make sure the valving stack height is correct. This means the nut has full engagement but doesn't run out of thread onto straight shaft. Refer to picture on page 173.

Apply a small drop of Loct~e to the rebound valving nut.

181

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0 z (/) m :a < C'i m c m :: =: ~ m ~

~ z w :Ii: ~

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182

Make sure the mid-valve/check valve is free lo move up and down.

Torque the rebound valving nut

Fully pack the rebound rod thread with grease. Remove excess grease.

Insert the rebound rod into the cartridge.

Quickly push the end of the damping rod through the seal using a T-handle.

Fill with fluid about 1 OOmm (4 j from the top.

183

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~ z w :Ii: ~

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184

Bleed the cartridge by pumping the rod in and out of the cartridge. Make sure you stroke it slowly on compression to avoid causing cavitation.

Replace the damping rod jam nut (see page 17 4) and set the oil level with a fork oil level tool.

This amount of oil is actually too much oil. The excess will be removed further in the procedure.

Insert the compression valve assembly.

Push down on the compression assembly and tighten. This will take a b~ of force because there is excess oil and you are compressing the pressure spring. Install the jam nut on the rebound rod.

Set oil volume by compressing the cartridge all the way. The reservoir piston will move up until the piston no longer seals on the shaft where the "necked-down" portion of the shaft is. This is called the "assembly groove" on figure 3.32. Extra oil will go past the reservoir piston.

185

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i5 z Cl) m ~ c=; m c m

~ =: 3: m ~

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~ w c:\. en ;:) en

186

Note: Some of the excess oil may drip out of the vent holes as the damping rod is compressed and excess oil is forr;ed out through the assembly groove.

Release pressure-make sure the rod extends completely.

Pour out excess oil.

Grease the fork seal and wiper.

Use the comer of a heavy gauge plastic bag and place n on the end of the fork tube. This will protect the seal from the sharp edges of the inner bushing groove.

Slide on seal and wiper over plastic bag. Pulling the bag taut will further smooth the sharp edges, preventing damage. The seal and wiper are directional, so make sure they are on the right way wnh the dual-lipped part of the seal facing away from the fork bottom and toward the outer fork tube.

187

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m ::J:I < c=; m c m

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188

Install the seal washer and outer bushing. There is usually a sharp and a rounded edge on the washer. I like to put the sharp edge toward the bushing. Sometimes the seal washer is more elaborate than a plain washer. If it is a machined part, make sure it goes on in the right direction.

Install the inner bushing into its groove.

Install the outer bushing with the seal driver. You will be hitting on the seal washer, and it will drive in the bushing .

Install the oil seal with the seal driver.

Install the clip.

Seat the clip in the groove with the clip tool or a small screwdriver.

189

(I) c: (I)

-0 m z (I)

i5 z (I) m :J:I < c=; m c m ;g =: 3: m ~

Slide the spring onto the cartridge and insert it into the fork tube.

The next step in measuring the preload is to gently rest the cartridge on the spring. Make a reference measurement between the end of the bottomed-<iut fork tube and any easily identified edge on the cartridge. (Ex: 105mm) This measurement will be drawn in when the bottom bolt is installed by the amount of the preload.

Compress the spring and insert the clip tool.

191

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~ =: 3: m ~

1-z w :Ii: I-

~ w c w u > a: w (/)

z 0 c;; z w Cl.. (/) ::::> (/)

192

Put a drop of Loctite on the damping rod thread.

Screw on the rebound adjuster bolt. Use a screwdriver to hold the adjuster screw in position while turning the adjuster boll This protects the 0-shape rod as we did during disassembly.

Tighten the jam nut.

Compress the fork and remove the clip tool.

Put a drop of Locttte on the adjuster bolt.

Tighten the rebound adjuster bolt wtth a torque wrench to manufacturer's spec.

193

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0 z (/) m :a < C'i m c m :: =: ~ m ~

~ z w :Ii: ~

~ w c w u > a: w (/)

z 0 <n z w Cl.. (/) ::::> (/)

194

The last step in measuring preload. Now that we have tightened the cartridge, the spring is compressed to the set length. Re-measure the reference distance (ex: 99mm). K we subtract this from the first reference measurement, this gives us the preload (ex: 105mm - 99mm = Smm of preload. We can also calculate the set length as ij is the free length minus the preload (493mm - Smm = 487mm set length).

Continuing the assembly, measure oil volume wijh a graduated cylinder. For these for1<s we cannot measure the oil height, so volume is the only option. Do not use a large-diameter measuring device or one that is tapered as they are not as accurate as needed.

Pour oil into the open tori< tube. Let the graduated cylinder drain completely.

Tighten the for1< cap.

Set the rebound adjuster located on the bottom of the fork leg. Again zero is fully clockwise (all the way in.)

Set the compression adjuster by counting clicks or turns outward (counterclockwise) from all the way in. Be careful to just gently bottom the needle in its seat as ~ is easy to damage the tapered needle.

Let us not forget the essential last step. Install the protective sticker. Be sure orient the sticker as to properly locate the bleed screws on the for1< cap.

195

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0 z Cl) m ::a < (') m Cl m ~ ::a .... 3:: m ~

... z I.LI :ii: ... ~ I.LI c I.LI ~

> a: I.LI en z 0 Ci) z I.LI a.. en :::> en

PROJECT 4 Emulsion Shocks

0 Skill Level: ' ~ Tools: Basic Tools, Shock Spring Compressor W (TFSC series), Pin Spanners (TMPS series)

for some models, Shaft Holders (TFSH if removing shaft from eyelet clevis), Seal Head Tools (TSSS series), Clip Tool (TSCP), Seal Head Bullet (TSSB), Nitrogen Station (see tools section), Bike Stand/Jack

Emulsion shocks are found o n all rypes of motorcycles and ATVs, dirt and srreec. T hey are rypical on mosc vincage models as well as many modern bikes. This mosc basic shock design is fa irly scraighcforward co work on, wich no piscon or bladder

co separace che o il and nicrogen. Service Tip: Inspect the bushings at the mounting eyelets carefully. Rubber b11shings degenerate over time, resulting in a loose feel

to the rider. Needle or spherical bearings can do this too. They can also seize up, cattSing binding and resulting in a harsh feel to the

rider. Don't overlook them.

196

-----------------------_,.....,...., Remove the spring and depressurize the shock using the

Shock Nitrogen Needle tool. It is also common lo use a Schrader (lire) valve .

Unscrew and remove the seal head assembly with a RT Pin Spanner. Some models will have a hex instead of pin holes. Some models have a pressed on cap and a seal head held in with a cl ip as is shown in the reservoir shock section.

Remove the shaft assembly.

Dump out the oil.

Clean everything, replace seals if needed, and refill the shock body with oil.

197

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1-z w :=:: I-

~ w c w u > a: w (/)

z 0 <n z w Cl.. (/) ::::> (/)

198

Adjust the lube extension on the Race Tech Pro Fork Oil Level Tool to the required oil level.

Set the oil level. This is critical as there must be more air space than the volume the shock shaft displaces (see Figure 3.34).

Insert the shaft assembly into the shock body.

Tighten the seal head with Race Tech Pin Spanner.

Pressurize the shock with the nitrogen needle.

Compress and make sure the shaft extends completely. Nole: Make sure emulsion shocks are mounted body up.

199

(I) c: (I)

"ti m z (I)

i5 z (I) m ~ c=; m c m

~ =: 3: m ~

!z w :IE I­CC

if w c w 0

> cc w Cl)

z 0

~ w ~ Cl) ::I Cl)

PROJECT 5 Reservoir Shocks

0 Skill Level: ' '

Time: B

~ Tools: Basic Tools, Shock Spring Compressor W (TSSC series) on most models, Pin Spanners

(TMPS series) for some models, Reservoir Cap Puller (TSCT 01 ), Shaft Holders (TFSH) if removing shaft from eyelet clevis, Seal Head Tools (TSSS series), Clip Tool (TSCP), Seal Bullet (TSSB), Nitrogen Station (see tools section), Bike Stand/Jack

Reservoi r shocks are modern, high-performance designs used on all types of motorcycles and ATVs, bo th dirt and street. These shocks may or may not have an external reservoir. They may use either a bladder or a floating piston or even a

diaphragm to separate the oil and nitrogen. Service Tip: Aluminum-bodied shocks can suffer wear to the hard anodizing, resulting in oil contamination and body wear. Some

aluminum body shocks come without any anodizing. If the oil is inky and black, carefully insp ect the anodizing. In many cases they can be re-hard-anodized. Be sure to check hoses and fittings on remote reservoir models when inspecting for wear and damage.

Disassembly

Place the end of the shock body in a vise, using Race Tech Aluminum Vise Jaws, or secure using the shock eyelet without special vise jaws. Be careful not to crush the shock body. Hint Check clicker positions on dampers and note settings.

200

Remove the spring with a Race Tech Shock Spring Compressor or remove the spring by unscrewing the preload collars with an RT Shock Preload Adjusting Tool. For street bikes and shocks with high spring rates (1 Okg/mm or more), use TSSC 02 Spring Compressor.

Remove the spring retaining clip with the Race Tech Shock Clip Pick Tool. There are other styles of retaining clips as well.

Remove the spring and collar.

201

(I)

c: (I)

"ti m z (I)

i5 z (I) m ~ c=; m c m

~ =: 3: m ~

!z w ::E ..... a:;

f w Cl w u > a:; w en z 0

~ w Q,. en ;:) en

202

Compress the shock and make sure it returns completely. tt not, then there may be a blown shaft seal, a bad bladder, a low-pressure bladder, or an improperly located piston (on piston style shocks).

Remove the nitrogen pressure from the reservoir and remove the valve with a valve core removal tool. Sometimes a Nitrogen Needle Tool is required instead of a valve core tool. In this case the Nitrogen Needle Tool is inserted into the opening to bleed out the pressure.

Depress the reservoir cap using a socket and a hammer. Many VZs can use a TSRC 01 Reservoir Cap Setting Tool to protect the Schrader Valve. On some models the cap is threaded on instead of being held in with a clip. Unscrew this type.

Remove the reservoir dip with the dip tool.

Remove the reservoir cap with the Race Tech Reservoir Cap Removal Tool. Make sure the tool is screwed on all the way. (Alternatively you could use compressed air to blow the cap off.) For WP shocks with a threaded cap, use a pin spanner.

Remove the shock body cap with a sharp wood chisel. Some models screw on, so don't get too excited with the chisel unless you are sure. Note: Most Showa, KYBs, and Oh/ins are pressed on. Penske, Works Performance, and early Oh/ins are screwed on.

203

Cl) c: Cl)

"ti m z Cl)

i5 z Cl) m ~ c=; m c m

~ =: 3: m ~

1-z w :Ii: I-

~ w c w u > a: w (/)

z 0 <n z w Cl.. (/) ::::> (/)

204

Compress the seal head to expose the circlip with the Race Tech Shock Seal Head Setting Tool. Some early WPs have a cirdip underneath the seal head as do some Yamaha shocks. The WPs are easier as the top piece screws on. The Yamaha has a clip on the top and sandwiches the seal head assembly between it and the bottom one.

Remove the seal head circlip with the clip tool. For shocks with a threaded seal head cap, use a pin spanner.

Remove the shaft assembly from the shock body by tapping with a plastic mallet. ~ it is stubborn, you can clamp the clevis in the vise and tap downward on the body.

Empty oil from the nitrogen reservoir and the shock body.

Remove peening with a flat bastard file (I just like saying flat bastard). File the outer diameter of the peened area down to the root of the thread. On Showas it is critical not to grind off the top flat as it holds in the rebound mechanism. Most KYBs can be ground flat.

Remove the shock shaft nut.

205

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~ =: 3: m ~

1-z w ~ I­CC

~ w 0 w u > cc w (/)

z 0 <n z w Cl.. (/)

:I (/)

206

Remove the valving stack.

Chamfer the end of the shock shaft.

Blow out the center of the shaft to remove any particles.

Note the correctly dressed shaft end. Beeeeeeeaut~ul!

Remove the seal head, body cap, bottom-out bumper, and retaining cup. Some models have slightly different hardware.

207

(/) c: (/) ,, m z (/)

0 z (/) m :a < C'i m c m :: =: ~ m ~

... z LU :ii: ... a: ~ LU c LU ~

> a: LU en z 0 Ci) z LU a.. en ::::> en

Behold the Shock Shaft Hall of Shame. From top to bottom: Bent shaft caused by ramming after linkage bolt came out; vise grips are not for holding the shaft end; and two examples of worn-through hard chrome from extreme use. Hint: don't take off shock mud flaps .

Note: A bottom-out bumper is a consumable item-only the one on the right is still usable. Always inspect your bumper and replace it if necessary.

208

Polish the shaft with 500- or 600-grit sandpaper.

H the seal is being replaced, begin by removing the top-out spring from the seal head (for shocks that have one.)

Remove the top-out bumper with a clip tool.

209

(/) c: (/)

-0 m z (/)

i5 z (/)

m ::J:I < c=; m c m

~ =: :!: m ~

~ z w ~ ~ cc ~ w 0 w u > cc w en z 0 <n z w Cl.. en :I en

210

Remove the top-out bumper. Nole: Some models do not have these pieces.

Remove the shock shaft oil seal.

Remove the dust seal. Note the notch in the vise jaws. ~ you hold the seal head w~h the top surface below the top of the vise jaws, you can pry on the edge of the jaws.

Inspect the shaft bushing and seal head 0-ring. Replace them ff they are damaged or worn. Bushing drivers are available.

This photo shows an exploded view of the seal head before assembly. Note the direction of the seal and other components.

211

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~ z w ~ ~ cc ~ w c w u > cc w (/)

z 0 <n z w Cl.. (/)

:I (/)

Reassembly

212

Install the dust seat on the head with an appropriately sized socket.

Grease the seal with Race Tech Ultra Slick Grease.

Reinstall the seal head with the Shock Seal "Bullet" Tool.

Clean the valving assembly in contact cleaner.

Surface the base plate on 220-280-grit sandpaper on a piece of plate glass.

Inspect the valving stack for any warped, dished, or creased shims.

213

(/) c: (/) ,, m z (/)

0 z (/) m :a < C'i m c m :: =: ~ m ~

1-z w :Ii: I-

~ w c w u > a: w en z 0 c;; z w Cl.. en :::> en

214

Install the compression valving stack.

Surface the piston on both sides. Inset: Note that the compression side of the piston is the one on the right. It has larger ports and larger diameter shims than the rebound side. Most, ff not all, pistons are directional.

Install the piston and rebound valving. Use a Race Tech Gold Valve (inset) for improved damping action and tunability.

Surface the rebound top plate and install it on the shaft.

Use Loctite on the shaft nut.

Check for proper stack height with the shaft nut and add an additional spacer (inset) if needed. Torque the shaft nut. The rebound base plate should cover the step at the end of the thread. The nut must have full engagement and not run out of thread onto the straight shaft.

215

Cl) c: Cl)

"'ti m z Cl)

i5 z Cl) m ~ c=; m c m

~ =: 3: m ~

!z w ::E ..... a:;

f w Cl w u > a:; w en z 0

~ w c:\. en ;:) en

216

Pour Race Tech Ultra Slick Suspension Fluid into the reservoir first.

Reinstall the valve core and bladder onto the reservoir cap.

Make sure there is enough oil so that when the bladder goes into the reservoir ~ overflows .

Push down on the bladder cap until the circlip groove is exposed.

Reinstall the reservoir clip in the groove.

Use the reservoir cap tool to seat the reservoir cap on the clip. This can also be done wtthout the cap tool by using compressed air. ~you use this method, gently bring up the pressure and make sure the clip is property located. Use compressed air to pressurize the reservoir to 20-40 psi to over expand the bladder.

217

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~ =: :!: m ~

~ z w ~ ~ a: ~ w Q

w u > a: w (/)

z 0 <n z w Cl.. (/)

:::i (/)

218

Fill the shock body with oil up lo about 50mm (2") from the top.

Install the shaft assembly into the shock body.

Top off the fluid to within 1 Omm of the lop of shock body.

Pull up very slowly and then push down firmly until no more bubbles show up on the compression stroke. ~ you pull up too quickly, the fluid will cavitate and you will not remove the bubbles. Make ~ look like you are really working hard-even if no one is watching.

Tip: Use a plastic mallet for shocks with extremely high compression damping lo open the valving stack and allow any trapped air past the piston.

Once it's bled, extend the shock and top ii off with fluid. Note: Make sure the low-speed rebound inlet port stays submerged at all times to avoid introducing air bubbles.

219

Cl)

c: Cl) ..,, m z Cl)

0 z Cl) m :::c < 0 m 0 m ~ :::c -I s: m :!$

220

Push in the seal head with the seal head setting tool until the 0-ring seals.

Once the 0-ring seals, depressurize the reservoir bladder while keeping downward force on the seal head. The volume displaced by the seal head will cause the overextended bladder to collapse back to its normal relaxed shape.

Push down the seal head until the circlip groove is exposed. An alternative to this method is to use a vacuum fill tool (TSVM 01). If used properly this will do an excellent job of removing trapped air and even some of the air that is in suspension in the fluid. With a vacuum fi lling tool the shock can be assembled dry. Be sure to follow the instructions carefully to trap the correct nitrogen volume.

Install the cirdip carefully into the seat.

Gently pressurize the reservoir and make sure the seal head and cirdip are properly seated. This method will also work for most piston reservoirs. Two-piece and threaded seal heads require positioning the piston before installing the seal head.

Tap in the shock body cap. Note: The drain hole should be aligned with the shock body eyelet so that ii will be al the lowest point when installed on the bike. Threaded-in seal heads should be torqued properly.

221

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~ =: 3: m ~

!z w ::E ..... a:;

f w Cl w u > a:; w en z 0

~ w Q,. en ;:) en

222

Compress the shock while depressurizing the bladder.

Fill up with nitrogen using the Pro Shock Nitrogen Gauge.

Bleed the shock to the proper pressure.

Stroke the shock shaft. The shock shaft should extend all the way. ~ n does not, the shock is probably underfilled or the shaft is bent Check the body and shaft as well. Stroke the shock to feel for proper function and smoothness.

~the seal head does not displace fluid as n is installed n will not compress the bladder the proper amount (or locate the reservoir piston properly). In these cases the bladder pressure should be reset to 4-Spsi before the seal head is installed. When in doubt, ask a pro.

Measure the free length of the spring.

Install the spring, retaining ring, and circlip.

223

(I)

c (I)

"ti m z (I)

i5 z (I) m ~ c=; m c m

~ =: 3: m ~

!z w ::E ..... a:;

f w Cl w u > a:; w en z 0

~ w Q.. en ;:) en

224

Adjust the collars to the desired set length for proper preload.

Tighten the lock ring wtth the shock preload adjuster tool. Grease the preload collar thread before installing the spring.

Line up the eyelets top to bottom. Make sure the adjusters are aligned correctly. Usually compression and rebound are on the same side but not always. Sometimes the shaft clevis has cutouts for linkage clearance. This is important.

Adjust compression (high-speed adjustment shown) and rebound clickers. Normally zero is all the way in and clicks or turns are counted as the adjuster is unscrewed (counterclockwise).

Chicks dig stickers.

225

Cl)

c: Cl) ..,, m z Cl)

0 z Cl) m :::c < 0 m 0 m ;g :::c -I s: m :!i

... z LU :::!: ... a: ~ LU c LU ~

> a: LU en z 0 (ii z LU "­en ::::> en

PROJECT 6 WP Progressive Damping System Shock

0 Skill Level: ' ' '

B't~.~. Time: C ~~.·

fj Tools: Basic Tools, Shock Spring Compressor (TFSC series) on most models, Pin Spanners (TMPS series), Shaft Holders (TFSH if removing shaft from eyelet clevis), Seal Head Tools (TSSS series), Clip Tool (TSCP), Seal Head Bullet (TSSB), Nitrogen Station (see tools section), Bike Stand/Jack

P rogressive da mp ing system (PDS) shocks are o ffe red by WP and O hlins, generally o n off-road m od els as well as snow

machines. T hey are unique in that th e damping increases as the shock compresses. To acco mplish th is they have some ex tra

internal compo nents. General servicing procedures a re the same as reservoi r shocks unless you a re plann ing to remove o r cha nge

the com p ressio n needle. We w ill show only the th ings that a re unique about this d esign.

Service Tip: ft is not necessary to remove the compression needle unless you intend to replace it with an upgraded high­

performance unit.

Disassembly

WP PDS shaft (right) ver.rns conventional shaft (left). Notice how the PDS shaft utilizes dual pistons.

226

Note shaft inner diameter size of the POS shock. This needle will plug the shalt as n is approaching bottom.

This is a POS valving layout.

When reassembling the valving assembly, position the spacer so that the feed ports on the sleeve are aligned wnh the ports on the shaft while the shaft nut is torqued.

227

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~ =: 3: m ~

..... z w :Ii: ..... ~ w c w u > a: w en z 0 <n z w Cl.. en ::::> en

228

tt charging the telescopic needle, use one of the RT TSST Series tools. There are three sizes.

This is the stock metering needle assembly .

This is the Race Tech Telescopic Needle. Apply thread locking compound on the retaining collar and a small amount of Race Tech Ultra Slick Grease on the Bellville washer during installation. The grease temporari ly sticks the washer lo the end of the needle.

Insert the needle assembly into the tool.

Insert the tool w~h the needle assembly into the shock. Tighten the needle assembly to specffication.

Remove the reservoir cap with the Race Tech Pin Spanner. Use the largest pins that will m into the pin holes.

229

Cl) c: Cl)

"ti m z Cl)

i5 z Cl) m ~ c=; m c m

~ =: 3: m ~

!z w :IE ..... a:;

f w Cl w u > a:; w en z 0

~ w Q.. en ::l en

Reassembly

230

To remove the piston from the reservoir there are two options. Option one: remove the piston by pushing a small screwdriver through the bleed port at the top of the reservoir. Option two: remove the piston with the WP special tool that threads into the piston.

After reinstalling the bleed port screw, make a sleeve tool by cutting a piece of .12mm (.005") shim stock and wrapping it around the inside of the reservoir. This is because there is a threaded area with a lip that will tend to catch the piston band, keeping it from slipping into the reservoir. Pour the proper suspension fluid into the reservoir until it is ful l. ij the piston is being replaced with a RT Bladder Conversion, the shim stock is not necessary.

Install the reservoir piston using your new sleeve tool. Instead of making a sleeve tool you could try holding the piston ring into the groove with a bit of heavy grease.

Push the piston down until the piston band engages the reservoir.

Bleed all the air from the reservoir. Invert the shock and push the reservoir piston into the body. Trapped air will be pushed out. Be sure to collect and re-use this new oil.

Pour oil into the body with the reservoir positioned below the shock body, as shown.

231

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0 z Cl) m ::J:I < c:; m Cl m

~ ::J:I .... 3:: m ~

~ z w ~ ~ cc ~ w c w u > cc w (/)

z 0 c;; z w Cl.. (/)

:I (/)

232

Fill the shock body with oil to a height of 40mm (1 W).

Lightly grease the 0-ring and install the reservoir cap.

With the Allen bolt loosely installed, attach the Race Tech WP Nitrogen Charging Tool. Push down on the tool as you tighten the holding clamp.

Charge the reservoir with nitrogen lo approximately 50 psi. Tighten the Allen bolt.

Rll the shock body with oil to about 40mm (1 W) from the top.

Insert the shaft assembly into the shock body.

233

(/) c: (/) ,, m z (/)

0 z (/) m :a < C'i m c m :: =: ~ m ~

1-z w :Ii: I-

~ w c w u > a: w (/)

z 0 <n z w Cl.. (/) ::::> (/)

23

234

Rapidly and forcefully compress the shock shall

Tip: When installing a heavy compression damping stack, tap the end of the shock clevis to open the compression valve to allow trapped air past the piston.

Top off the oil.

Install the seal head with the Shock Seal Head Setting Tool (TSSS 02) until it can no longer go in. Maintain downward force on the tool while simultaneously releasing nitrogen pressure from the reservoir.

Install the retaining clip.

Pressurize the shock lo the manufacturer's specification.

235

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~ =: :!: m ~

1-z w ~ l­a: ~ w c w u > a: w (/)

z 0 (ii z w Cl.. (/)

:I (/)

236

Tighten the Allen bolt with the knob on the tool.

Install the end cap by tapping it with a soft-faced hammer. The drain holes should be aligned with the shock body eyelet so that it will be at the lowest point when installed on the bike.

There are two alternatives to using the Race Tech or original equipment WP Shock Charging Tool. The first is the SPNV 0512 Nitrogen Valve Bolt. It replaces the stock Allen screw (left) and is charged with a Nitrogen Needle (shown). Second is a SWBL Series shock bladder conversion kit with a reservoir cap that uses a Schrader valve (right).

These two photos show the piston displacement prior to and after the seal head installation. Notice that in this case the displacement of the seal head into the shock locates the piston in the reservoir automatically.

Verify the piston height after the seal head has been installed.

237

en c: en ~ m z en 0 z en m = < 0 m 0 m ~ = -I s: m :!i

>< c z ..... a.. ~

Appendix 1

LOWERING Lowering can be required fora number ofreasons: co uching rhe ground, wheelie conrro l (such as in drag racing), convening a bike from o ne genre ro anorher (M X to flar rrack, supermoto, o r road race) , and geomerry changes are rhe main ones.

In some cases lowering is as simple as rhe addi rion of special spacers in borh rhe fo rks and shock. In orher cases iris quire invo lved, including changing o r modify ing springs and cusrom machining.

Suspension lowering can be done on all rebuildab le suspension-some models have suspension rhar is nor rebuildable. T his is more of a problem wirh rhe rear suspension com ponenrs, rhough some fo rks have sealed carrridges.

In some cases rhe solurion on rhe rear is ro build shorrer custom shocks wirh less rravel. Lowering rhe suspension can also be done in rernally using spacers. U lrimarely, lowering a bike means sho rrening rhe shock and fo rks. Lowering is reversible, so if you don'r li ke ir, you can always rerurn to rhe stock heigh r.

In general when lowering a mororcycle, borh rhe fronr and rear end should be lowered rhe same amounr. G.M. D.

Compurrack is a good resource ro check for proper geomerry.

As an added benefit, c hassis alignment is measured at the same ri me.

If rhe bike is being lowered so rha r rhe rider can touch rhe ground, I normally recommend lowering 25 mm ( I inch) to begin wirh. Riders are consranrly surprised how much of a difference rhis amounr makes. T he reason only 25mm is recommended is rhar rhe loss of ground clearance, cornering clearance, and suspension rravel (rhe abili ry to deal wi rh bumps and holes) becomes more of a prob lem rhe lower yo u go.

However, if rhe rider is wi ll ing to deal wi rh rhose shorrco mings, bikes can be lowered significanrly mo re. T he absolure limir to loweri ng is rhe o riginal borrom-ou r poinr. Keep in m ind rhar rhe more a bike is lowered , rhe more likely new sp rings will be req uired (more o n rhis in a momenr).

Some srreer models are already lowered. On rhese models furrher lowering should be considered carefu lly befo re proceeding, as ground and cornering clearance is a bigge r issue.

Ler me make rhis nex r poinr in rhe srro ngesr rerms I can: I do not recommend lowering links! T hey do no rhing to decrease rhe rravel , meaning rhar rhe rire can borrom our rh rough rhe fender. This has che porenrial to stop rhe rear wheel from rurning a nd, if rhis happens, ir can cause a crash. Lowering lin ks can somerimes be used if rhe shock rravel is shorrened rhe app ropriare amo unr w irh exrernal rravel limi rers. H owever if rhe shock has ro be raken aparr, rhe

lowering can be done inside rhe shock wirhou r rhe added expense of rhe lowering link.

238

Keep in mind rhar shorrening rhe shock by 5mm does nor lower rhe rear end 5mm. T his is because of rhe leverage ratio of rhe linkage o r geomerry of rhe shock mounring. In general, mosr modern d irr bikes have an inirial leverage rario ranging from 3.1 ro 4.0. Wirh a 3. 1 leverage ratio, a 3mm spacer would lower rhe rearend 3 .1 rimes rhe spacer lengrh, o r 9.3m m arrhe wheel. This relarionship is imporranr in making rhe proper lengrh spacer.

O ne easy way ro measure required shock spacer lengrh is as fo llows: remove rhe spring and slide rhe borrom-ou r bumper up all rhe way unril ir conracrs rhe shock body end cap. Then compress rhe rear wheel ro creare rhe desired lowering amounr- rhis will move rhe borrom-our bumper. You can rhen measure rhe required lengrh of rhe inrernal spacer: as ir is rhe disrance rhe bumper has moved. The spacer is rhen insralled inrernally berween rhe rop-our plare and rhe seal head. T he spacer should be made in suc h a way as ro allow o il flow ro rhe low-speed rebound adjusrer. Race Tech produces spacers in 2 and 3mm inc remenrs rhar can be scacked in I mm incremenrs. If you'd rarher do ir yourself, a

single, solid spacer can be machined. Sha rrer springs may be required for rhe reduced lengrh

of rhe forks and shock. For example, if rhe fo rk does no r have

a spring spacer o r the shock preload collars cannot be backed off far enough ro creare rhe proper preload, you're go ing ro need new springs.

If rhe rider wanrs ro have the srock spring force, rhe spring rare must be increased. Here's how to cak ulare the ra re required: rake rhe original correcr spring rare ri mes the o riginal n avel divided by che new travel. k2 = k, x (d ,ld 2) T he "correct" spring race is affected by personal preference, and many riders prefer che decrease in borro ming resistance.

Keep in mind char che com pressio n da mping's concriburion ro borroming resistance will be d im inished wirh decreased rravel. This means rha r mo re compression dam ping is required ro resisr bo rroming, bur rhis will result in a harsher ride. Once again, rhis is affecred by rider preference, as many riders do n'r wanr ir harsher. On rear shock srreer app lications, lowering 25 mm may nor cause much of a n issue as borro ming resisrance is rarely a prob lem .

F450 Moro Conversions (convening a morocross bike inro a road race bike) require borh lowering and bortoming poinrchanges.This means rhe botro m-ou rbu mper issho rrened and moved as well. T he spring rares are rad ically changed and the geomerry is se t up, so th is is a job fo r experrs.

Anorher solution for gaining inseam clearance is shorrening and/or re-contouring rhe sea r. This can be done fo r di rr bikes as well as srreet bikes. Sear re-conrouring is relarively inexpensive as well. The widch of the sear is also imporranr: rhe wider rhe seat, the harder it is to touch the ground. If altering the seat does the trick, it might be the best so lution .

M

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Appendix 3

GLOSSARY

an odizing

A coaring on alumi num. Tr can be cosmeric in naru re, as

wirh color anodizing, or it can be funcrio nal as wirh hard

anod izing.

anti-high side device

A long, soft, to p-o ur spring used in road race shock absorbers

insread of a top-our bumper. Developed by Ohlins.

anti-dive system

A mechanical o r hydraulic device inrended to decrease rhe

amo unr the front end dives u nder braking . T he hyd raulic

rypes vary in des ign bur all increase rhe compression damping

when rhe brakes are applied. M ose are acruared by rhe braking

force o n the wheel cylinders or the hyd raulic pressu re in rhe

b rake li nes. Q ui te commo n o n large b ikes in the 1980s, they

are now rare because they create even more harshness on the

square-edge bumps. As o f this printi ng ch is rype of system is

still used on Gold W ings.

axle offset

T he distance between the cen terl ine o f the fork ru be and the

center o f the front axle perpendicular to the cen ter line on o ffse t axle forks (mostly used on di rt bikes).

240

base plate

A thick was her o r plate that the valving sh ims resr o n.

base valve

T he compressio n valve assembly o n carrridge fo rks o r older

sryle twin-rube shocks.

bladder

A flexible mem brane separating rhe suspensio n fluid fro m

rhe n irrogen in a shock absorber. Allows the shock to be

p ressu rized to eliminare caviratio n.

bladder reservoir

A sryle of reservoir where rhe fluid and rhe nitrogen are

separared by a flexible membrane.

bleed (or bypass)

A free- flow o rifice chat allows fluid to pass easi ly ar low flow

races. le is usually rhe lowest speed circuit.

bottom-out bumper

A rubber o r urethane bumper com monly used in shocks to

cushio n rhe shock when ir uses up all rhe travel on compression.

This functio ns as a second spring in parallel wi th the main

spring and adds ro the total spring fo rce. Typically made our of

rubber o r urethane, rhey are prone to break down after awhile

and should be rep laced .

bottoming Using up the tota l avai lable t ravel of the suspensio n system.

bottoming cone A hydraulic device designed to give additional damping resistance when the fork or shock reaches bottoming.

cartridge fork A more sophisticated type of fo rk than a damping rod fork. It utilizes p istons wi th shims that bend to create compression and rebou nd damping. The basic design a llows the manufacturer to p rod uce a less progressive damping curve than a damping rod fork. Nore: Some cartridge fo rks with poorly designed valving crea te very similar curves to damping rod forks.

cavitation Cavitation is the format io n of vapor bubbles in a flowing liq uid caused by a decrease in pressure (spec ifica lly in an area w here the p ressure of the liquid fa lls below its vapor pressure) . T his is the sam e pheno menon as boiling however not du e ro the addi tio n of heat but to a decrease in pressure. Cavitation creates loss of both compression and rebound damping.

center of gravity

T he location at which the entire mass of an object can be rep resented by a single force acting on that point.

check valve A one-way valve that easily opens in one direction and shu ts

off completely in the other d irectio n.

clamping shim T he last shim in a valving stack, farthest away from the piston and closest to the base plate. All the other shims must bend o n the clamping shim.

clickers External damping adjusters. These usually control low­speed rebound damping or low-speed compressio n damping o n fo rks. On shocks the clickers usually control low-speed rebo und and high-speed compressio n damping. Many bikes have no clickers. Nore: Some clickers don't click so yo u wo uld count "rums" instead. Unless o therwise marked ,

most adjusters create maximum d amping when they are screwed all the way " in" (clockwise), and therefore cou nted as clicks (usually quarter rurns) "out" (counter clockwise from all the way in).

compression Suspension movement when rhe wheel hits a bump and compresses. Also known as the bump stroke.

compression bolt assembly The complete compression valve assembly. Also known as the base valve in a cartridge fork.

compression damping (aka bump or jounce damping) Damping created on the compression stroke as the suspensio n is collapsing. Because damping is sensi tive to velocity, the terms low-speed compressio n damping and high-speed compression d amping are often used.

crossover shim The small diameter shim in a two-stage va lving stack that separates the low-speed stack from the high-speed stack.

cylinder valve An additional compression dam ping circui t located at the top of the cartridge on some 1998 through 2004 KYB dirt bike fo rks (most notably on YZs and C R1 25).

DLC See diamo nd like carbon

damper See shock absorber

damping (a.k.a. dampening which the purists don't li ke to use as it also means to make something wet.) Fluid resistance to

movement. T he force is created as o il passes through holes or other types of valving systems. The amount of damping force is dependent on the particular valving configu ration and the viscosity of fluid used. Key po ints: T he amount of damping created is determined by the speed at which the suspensio n is compressing or extending. Damping cums mechanical energy into hear.

damping circuit A physica l pach for suspensio n flu id char creates resistance. T here may be five o r more compression circuits and chree o r m ore rebou nd circuits in a shock or cartridge fo rk. T he effect of each circui t genera lly overlaps, crea ting m assive flexibili ty, while sometimes making for complex adjustments, as well.

damping piston The va lve that che shims are stacked on . le is sealed on ics

ou ter diameter with a piston ring or o- ring. T he piston ring is usua lly made of a Teflo n composite if the piston is s liding in a chamber (as w ich a shock or che rebou nd

piston o n a cartridge fo rk). On a compression piston on a ca rtridge fo rk ic is stationary and therefore is sea led with an o-ring.

241

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damping rod fork A simple type of fo rk that utilizes a rube with ho les in it to create compression and rebound damping. T he basic nature o f creati ng damping by shoving fluid th rough holes produces a damping curve that is excessively progressive, resulting in ha rshness and bottoming.

DeCarbon shock A high-pressure monorube shock absorber invented by C hristian Bourcier de Carbon in 1953. Ir uses a floating piston to separa te the o il from a high-pressure gas (usually nitrogen) to minimize cavita tion during high-velocity suspension movement. This term has loosely been referred to any shock with a piston or memb rane that separates the oil from the gas.

Delta Valve An afrermarker fo rk valve from Race Tech that has externally adjustable low-speed and high-speed compression damping, used primarily on dirt bikes.

diamond like carbon An impressively hard surface coating wich an extremely low coefficient of friction. Commonly used on fo rk cubes and shock shafts.

diving T he phenomenon of che front forks compressing during braking. Many linkage-type alcernacive front ends control dive mechanically. The ce rm usually implies excessive diving.

dual-rate Typically refers to a spring char has closely wound evenly spaced coils, as well as evenly spaced, wider-gapped coils. As che spring compresses, che eight coils contact each ocher and are "blocked our," thus reducing the effective number of coils

and creating a stiffe r rare. T his results in one spring with two rares. Dual rate spring setup can also be created by stacking springs and controlling the crossover.

dynamic friction Friction where there is movement between che surfaces.

Emulator See Gold Valve Camidge Emulator.

emulsion A mixcure of o il and air. Emulsion shocks do not have a membrane or piston between che fl uid and che nitrogen . T hey a re less expensive to produce chan a rese rvoir shock. T hey a re expected co foa m up and create consiscenc damping. T hese a re nor high-performance shocks.

242

fork bushing A low frictio n, load-bearing sleeve. Modern fo rk bushings consist of a steel band wi th a coating of bronze and a layer ofTeflon bo nded on it. Most fo rks require two per leg. Early telescopic fo rks did not have these bushings and therefo re suffered from even mo re friction than current designs.

free length The length of a spring fully ex tended (nor mounted on the shock or in the forks, with no load on the spring).

free sag aka bike sag, unladen sag-T he amount the bike settles under its own weight (with no rider). If static sag is correct and there is too much free sag, che spring is too stiff (nor too soft) .

friction Mechanical sliding resistance. Friction turns kinetic energy into heat. Its magnitude is calculated using the fo rmula:

F = u x F., where: F - Frictional force. u - Coefficient of friction. (This depends on which ma terials are in contact wi th each o ther. For example, rubber on steel will have a higher coefficient than steel on steel.)

F" - Normal force (the force perpendicular ro the surfaces in contact).

Gold Valve Replacement high-performance pistons for shocks and fo rks. Made by Race Tech.

Gold Valve Cartridge Emulator An afcermarker valve made by Race Tech used in a damping rod fo rk that creates the compression damping curve o f a cartridge fork. A.K.A. Emulator.

hard anodizing An elect ro-chemical process that deposits a very hard layer of aluminum oxide on an aluminum surface. T he layer builds up as much as it penetrates. T herefore a .002" coating penetrates .00 I" and builds up .00 l''. Ir can be applied in a limited number of colors as well.

harshness An uncomfortable jolt char occurs on th e compression stroke.

It can be caused by many different factors, including too much high-speed compression dam ping, too much friction, too much low-speed rebound damping causing packing, too high of a spring race, too much preload, binding from things like bent fork rubes, excess ive friction, poor suspensio n fluid, and poor suspension linkage bearings. I r can also be caused by excessive bottoming.

head shake An unnerving phenomenon where the fo rks oscillate back and forth rapid ly and sometimes violen tly. Ir can be caused by various facto rs, including a frame that is ou t of alignment or twisted, too li ttle "trail", underdam ped rebou nd , overdamped high-speed compression, anything that causes a bind, chassis flex, and swingarm flex.

high-speed compression clamping Compression dam ping created by fast vertical wheel movements. This occurs when hitting anything that has a square edge, such as pot holes, expansion jo ints, Bots Dots, some railroad crossings, or braking bumps particularly when the vehicle is travel ing at high-speed.

high-speed rebound damping Rebound damping that occurs when the vertical wheel movements are fas t. Since the fo rce that extends the suspension is primarily due to the spring, high-speed rebound occurs when there are large wheel movements. H igh-speed rebound is ofren produced when hitting big dips or gullies at speed . Of course, chain forces and the terrain will affect the rate of extension as well, so it is not solely determined by the amo unt of travel used.

inner bushin g

Also known as an RU bushing (as well as many other names), it fits onto the inner chrome fork tube and has Teflon on the outer su rface.

kicking Serious harshness that actually throws the wheel off the ground. T his can occur when hitting square edge bumps like pot holes or large expansion jo ints. Any of the factors that cause harshness can also cause kicking, but it is generally caused by too much high-speed compression damping a nd/ o r fr iction o r severe bottomi ng.

leverage ratio

The mechanical advantage of the wheel on the shock. It is the ra tio of the trave l of the wheel to the t ravel of the shock. It is also the ra t io of the force on the shock to t he force on the wheel. T he higher the leverage the less t he shock moves fo r a g iven wheel travel. T his requires higher dam ping and spring ra tes. (NOTE : Ir can also be defined as the opposite, i.e. as the ra t io of rhe travel of the shock to the t ravel o f the wheel.)

leverage ratio curve The plot of how the leverage changes through the travel of the rear wheel. T his change is caused by the mechanical linkage. Normally the leverage decreases as more travel is used up, creating more resistance due to the shock spring and the shock dam ping.

linear Straight line (no t necessarily flat).

low-speed co mpression damping Compression damping that occurs when the vertical wheel movements are slow, such as when going through a dip or gully or on the fo rks during braki ng particularly at low vehicle speeds.

low-speed rebound damping Rebou nd dam ping that occurs when the vertical wheel movements are slow. Because the fo rce that extend s the suspension is primarily due to the spring, low-speed rebound occurs when there are small wheel movements.

mid-valve An add itional compression circuit placed where the rebound check valve is usually located . Often used in dirt bike applications. If overdone it can add harshness and ca vi ta ti on.

nitrogen An inert gas used to pressu rize shock absorbe rs to help elim inate cavitation. Argon o r any inert gas could a lso be used.

normal force T he force perpendicu lar to the surface.

oil level A way to measure the amou nt of oil in a fork leg as opposed to measuring volume. T he oi l level affects the force created by air pressure as the fork compresses. The oil level is the distance from the top of the fork tube down to the top of the oil with the fork completely collapsed and usually with the springs removed.

outer bushing Also known as a DU bushing (as well as many other names), it fi ts onto the ou te r fo rk tube and has Teflon on its inner surface.

offset

A distance between two centerlines, typically referring to triple clam p or axle offset. Total Offset is the combination of Triple C lamp Offset and Axle Offset.

offset forks A n ex te rna l fork design where the ax le is off set from t he centerl ine of the fo rk. T h is is most common ly used o n di rt bikes .

243

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orifice A hole commonly used as a bleed in shocks and carrridge forks. Ir is generally rhe major source of damping in damping rod sryle forks. Orifices creare velociry-squared sryle force vs. velociry curves. In orher words, when rhe velociry is doub led rhe damping fo rce increases wirh rhe square of rhe velociry (ar a rare of four times). T his is rhe most progressive rype of damping fou nd in srandard shocks and forks.

packing W hen hirring a series of bumps rhe wheel exrends roo slowly afrer being compressed rhar ir does nor reru rn complerely when rhe nexr bump is encounrered. Ir is caused by excessive low-speed rebound damping.

piston reservoir A sryle of reservoir where the fluid and rhe nitrogen are separared by a floaring pisron.

piston ring A sealing ring on a shock pisron or a carrridge fo rk rebound piston. Usually made of a Teflon composite or a Teflon-coated steel band. le seals because of the pressure behind ic similar ro che pisron ring in a moror.

piston ring energizer o-ring

T he a-ring undernearh rhe pisron ring rhar provides an inirial load against che inner wa ll of che shock body.

piston rod (Aka damping rod or rebou nd rod) T he rod in a cartridge fork char attaches co che fork cap and usually also carries che rebound pisron.

po going Uncontrolled rebounding.

preload T he cerm preload has cwo meanings (length and force). In che motorcycle industry ir usually refers ro preload length.

preload adjuster A method of externally adjusting che preload. These can be ramped, threaded or hydrau lic. H ydrau lic preload adjusters on shocks allow remote adjustment o f che preload. Nore: When rhe preload adjusters are backed off all che way, chey do nor necessarily have zero preload. Wich forks in

parricu lar there is usually some preload at the minimum external preload setting.

preload force T he amount of force on the spring when it is at its preload

length.

244

preload length The amounr a spring is compressed from full exrension when installed wi rh rhe fork o r shock fu lly extended.

preload spacer Material used ro ser rhe preload in a fork. Thin-wall sreel or aluminum cubing is commonly used. Many afrermarket spring companies use PVC as spacer material, which works fine if the ends are finished flat and a steel washer is used o n boch ends of the spacer.

progressive Usua lly refers to spring rares, leverage ratio curves or damping curves. As trave l or velociry is increased, rhe resulcanr force increases slowly ac flrsr and more rapidly as ir goes up.

race sag See sea cic sag.

rake The angle of che steering axis from vertical, measured in degrees. For a given offset, there is more trai l if rhere is more rake. (NOTE: Some manufacturers [KTM] measure rake from horiw ncal.)

real trail (also see trail)

The self-srraighrening characrerisric builr into fronr-end geomerry. le is rhe perpendicular distance between che sreering axis and the center of che poinr of conracc of che fronr wheel wich rhe ground . T his method is far superior ro standard "Ground Trail" or "Trai l". Trail is usua lly measured

in millimeters.

rebound Suspension movemenr when che wheel ex tends. Also known as tension.

rebound damping Damping created on rhe rebound stroke as che suspension is extending. Because damping is sensitive ro velociry, che terms low-speed rebo und and high-speed rebound are ofren used.

rebound rod

Aka damping rod in a carcridge fork.

rebound Suspension movement when che wheel excends. Also known as tension.

rebound damping Damping created o n che rebound stroke as che suspension is extending. Since damping is sensitive co velociry, che terms low-speed rebo und and high-speed rebound are ofren used.

reservoir A canister o r portion of a shock absorber with a membrane o r piston separating the fluid from a compressible gas. Usually fi lled with high-pressure nitrogen. This allows for displacement of the fluid by the shock shaft because oil is incompressible.

revalving C hanging the internal valves that create dam ping.

rising rate Usually refers to a leverage ratio curve. T he leverage of t he wheel on the shock decreases as the wheel goes through its travel.

sag See static sag.

set length The length of the spring installed in the fo rks o r on the shock with the shock fully extended. Free length minus preload equals set length.

shim (Aka valving shim) A thin washer made out of spring steel used in a damper to create hyd ra ulic resista nce. It is typically s tacked up in

combination with other shims of various thickness and dia me ters on a damping piston to create the requ ired damping curve.

shock absorber A hydro-mechanical device that uses a fluid to create resistance . Key point: The damping fo rce is sensitive to velocity. T he kinetic energy is co nverted to heat.

shock body T he outer cyl inder of the damping unit. Usually made of aluminum or steel.

shock bumper A mechanical cushion made out of rubber o r uretha ne,

designed to give additional spring-type resistance when the fork or shock reaches bottoming.

shock linkage A series of mechanical levers designed to change the leverage the wheel has o n the shock as it goes through its travel.

shock shaft T he main shaft in a shock absorber. The valving is on one end and the eyelet is attached to the o ther. It is typically hard chrome plated fo r durability.

single stage A single stage valving stack consists of a single continuous straight or tapered stack and an end o n the clamping shim .

spring A mechanica l device that sto res energy as it is displaced. It usually is in the form of a coil design but sometimes is a leaf design. C hrome silicon steel is typically used, but titanium and carbon fiber have been used as well. Ai r can also be used as a spring. Key point: Springs are position sensitive and store energy.

springrate T he stiffness of the spring (see also dual rate, linear and progressive). It is the slope of the load deflection curve.

K =_FI D K - Average Spring Rate (measured in kilograms/ millimeter or pounds/inch) _F - C hange in Force (in newtons, kilograms o r pounds) between two measurement points. _ D - C hange in Displacement (in m illimeters o r inches) between two measure ment points.

sprung weight (aka sprung mass) T he weight of the motorcycle above the spring. It includes part

of the spring weight.

static friction (aka stiction) Friction where there is no movement between the surfaces. Static friction is typically higher than dynamic friction though slight slippage can have the greatest frictio n.

static sag T he amount the bike settles vertically wi th the geared up rider on board in the riding position.

stiction See static fric tion.

straight stack

In this type of valving stack a ll shims are the same diameter until the crossover or clamping shim, which is smaller in diameter.

stressed member A part in a system that bears the load. T his term is commonly used when referring to an engine that is a structural load­bearing pare of the chassis as in most D ucatis.

245

~ -a m z c >< w

M

>< c z ..... a.. ~

suspension fluid Used inside a shock absorber for two purposes: ro crea re damping when fo rced rh rough orifices or valving, and ro lubrica re. Viscosiry and viscosiry index are im porranr quanriries. Key poinr: Oil is incompressible (nor exacrly, bur close enough for our discussions) .

swapping (Aka pogoing) A disconcerring phenomeno n where rhe rea r end of rhe bike oscillares back and fo rrh wirh large amplirude. Ir can be caused by a number of non-suspension related causes, such as a flexib le chassis or swingarm, low rire pressure, and misaligned chassis or wheels. Excessive high-speed compression or spring rate, or exrremely underdamped rebound cou ld also be the cause.

tapered stack T he valving shims gradually decrease in diamerer as rheir posirion gers farther away from the piston face. T his is primarily designed ro reduce the chance of rhe shims becoming permanently distorted or creased.

Teflon•

From DuPont (polyrerrafluoroerhylene or PTFE), a low­fricrion, dry-film lubricanr.

three stage T his valving stack is similar ro rhe two-stage srack bur has two crossover shims, resulring in a low-speed, mid-speed and

a high-speed stack.

titanium nitride An exrremely hard coaring commonly used to create long­weari ng rool bits, applied microns rhick to hard chrome fork rubes and shock shafrs to lower fr icrion . Ir does nor ad here to aluminum.

top-out bumper A rubber or urethane bum per commonly used in shocks to cushion the shock when ir becomes fully extended.

top-out spring A coi l sp ring commonly used in forks and some shocks (see anri-high side device) to cushion rhe fork when it becomes

fully exrended.

top-out valve A hydrau lic top-ou r device.

246

topping out When rhe fo rks or shock ex rend ro rhe limirs of rravel. T his can occur when rhe wheel gers airborne, bur ir can also happen during accelera tion or in a series of turns when rhe bike is flipped from side to side. Ir can also be caused by roo much preload on rhe spring. T his can happen when rhe spring used is too sofr and rherefore requires excessive preload to ger rhe correcr sag. Too much rebound damping can mask rhe problem .

trail (aka ground trail) (see real trail) The self-srraighrening characteristic builr into fronr-end geometry. Ir is the distance between two specific poinrs. One point is rhe intersecrio n of an imaginary line exrending through the centerline of rhe sreering stem and the grou nd . The second point is rhe center of rhe poinr of conracr of the fro nr wheel wirh the ground. Trail is usually measured in mi llimerers.

triple clamp offset The distance between rhe cenrerline of rhe sreering srem and rhe fronr axle perpendicular ro rhe sreering axis. T he more offser rhar is used, rhe less resulring trail will be fo r a given fo rk geometry. I r's usually measured in millimeters.

triple rate

See dual rate. Same concept as dual rate but with three races. The three distinct races are usually achieved by stacking three separate springs on top of each other.

twin chamber

A carrridge fo rk design where the cartridge is inverted and separated fro m the rest of a fo rk utilizing a spring-loaded, p iston-type reservoir manu factured by Showa. T he term is also loosely used to cover o the r brand of spring pressurized or air pressurized bladder forks.

twin tube shock

A sryle of shock that is very similar in design to a cartridge fo rk. The air space is located between the shock body and the ou tside of the cartridge. Ir is the most common rype of shock in use in automobiles today.

two stage This valving stack has a "crossover shim" in it. T he crossover shim is a small d iameter shim upon which the low-speed shims bend. T his allows the low-speed stack to open until the fluid flow increases enough rhar it hi ts the high-speed stack. When this occurs, rhe total stack stiffness is the combinatio n of the low-speed and rhe high-speed stacks.

unladen sag Sec free sag.

unsprung weight aka unsprung mass The weight of the chassis that must go up and dow n with rhe wheels as it co mpresses and extends. This includes everything below the springs, such as the wheels, axle, brakes, pa rt of the spring, and a portion o f the swingarm. The swingarm is mo re effectively measured as the rotational mass mo ment of inertia with respect to the swingarm pivot instead of the unsprung mass.

valving The mechanica l hardware that c reates d amping. T his can be a comb ina tion of ho les, ports, shims, springs, check va lves, etc.

valving stack A set of shims. Some examples of valving stacks are compression and rebound stacks. These may have subsets like low-speed compress io n, mid-speed compression, high-speed compressio n, low-speed rebound, and high-speed rebound. T he configuration may be single stage, rwo stage, three srage, etc., and may be tapered or st raight.

viscosity A fluids resistance ro flow or more precisely ir's resistance ro shear. H ow thick the oil is. Ir must be measured at a specific temperature because the thickness is sensitive to temperature. The rest equi pment contains a specific volume of oil and is held at a specific remperacure. le is chen a llowed to flow ch rough a specific size o rifice and rimed. T he longer it rakes, che thicker the o il. SAE 20, SAE 30, etc., refer to a range, nor

a specific viscosity.

viscosity index (Vl) A number that indicaces how much a fluid thins our as ic heats up. A higher number means the viscosity is more cemperature-srab le. A mineral base fluid typically has a V1 of 100. Fork fluid is usually around this number as wel l. High quality suspensio n fluids fo r rear shocks have a VI of 200 o r can be in excess of 400.

weight bias Typically fronc to rear weight bias. Can be laden or unladen (rider on or off) . The percen cage of fronc wheel weigh r to rear wheel weighc. T here is also a sprung weight bias char is used co calculate dynamic response of veh icles.

247

Appendix 4

RACE TECH MOTORCYCLE SUSPENSION BIBLE TESTING LOG

~

><

DATE

BIKE

RIDER

WEIGHT/SKILL

TUNER

FRONT

Spring Rate (kg/mm-n/mm-lbs/in)

Preload (mm)

Free Sag (mm)

Static Sag (mm)

Stiction Zone (mm)

Oil BrandNiscosily

Oil Level (mm)

Low-Comp Adj (dicks-turns)

Hi-Comp Adj (clicks-turns)

Rebound Adj (clicks-turns)

Fork Height Adj + I - (mm)

Tire Brand //Model

Tire Size

Tire Pressure (cold I hot ps~

LAP TIMES

~ RIDER COMMENTS ..... a.. ~

248

TRACK

CONDITIONS

WEATHER

TEMPERATURE

ALTITUDE

TEST 1 TEST2 TEST 3 TEST 4 TESTS

RACE TECH MOTORCYCLE SUSPENSION BIBLE TESTING LOG

DATE TRACK

BIKE CONDITIONS

RIDER WEATHER

WEIGHT/SKILL TEMPERATURE

TUNER ALTITUDE

REAR TEST 1 TEST2 TEST 3 TEST 4 TESTS

Spring Rate (kg/mm-n/mm-lbs/in)

Preload (mm)

Free Sag (mm)

Static Sag (mm)

Stiction Zone (mm)

Oil BrandNiscosily

Oil Level (mm)

Low-Comp Adj (dicks-turns)

Hi-Comp Adj (clicks-turns)

Rebound Adj (clicks-turns)

Fork Height Adj + I - (mm)

Tire Brand //Model

Tire Size

Tire Pressure (cold I hot ps~

LAP TIMES

RIDER COMMENTS

249

,.., >< c z ..... a.. ~

Appendix 5

RACE TECH TOOL LIST Item Number

TCPN 4301

TFBT 02S

TFBT 1010

TFBT 1010

TFBT 1212

TFCA 01

TFCA 02

TFCH 01

TFCH 03

TFCH 04

TFCH 06

TFCT 35

TFCW 02

TFCW 243241H

TFCW 4549

TFCW 4650

TFCW 50H

TFGC 500

TFHD 1724

TFHP 01

TFOL 02

TFPA 14

TFPA 17

TFPC 2328

TFSB 01

TFSC 01

TFSC 02

TFSCA01

TFSD 30

TFSD 33

TFSD 35

TFSD 37

TFSD 39

TFSD 41

TFSD 43

TFSD 46

TFSD 48

TFSD 50

TFSH 10

TFSH 14

TFSH 20

TFSH 32

250

Description

SWINGARM PIVOT NUT TOOL 4301

FORK BLEED TOOL SET

FORK BLEED 10x1.0 & 10x1.25

FORK BLEED 10x1.0 & 10x1.25

FORK BLEED 12x1.0 & 12x1.25

FORK CLICKER TOOL - THIN

FORK COMPRESSION SOCKET - R6

FORK CARTRIDGE HOLDING TOOL 01

FORK CARTRIDGE HOLDING TOOL 03

FORK CARTRIDGE HOLDING TOOL 06 R6

FORK CARTRIDGE TOOL - BPF 33/35mm

FORK TWIN-CHAMBER TOOL 35mm KYB

FORK CAP WRENCH WP 48 - 4 PIN

FORK CAP WRENCH 24/32/41mm HEX

FORK CAP WRENCH 45/49 OCTAGON

FORK CAP WRENCH 46/50 OCTAGON

FORK CAP WRENCH 50mm HEX WP

GRADUATED CYLINDER 500cc

HEX AXLE WRENCH 17, 19,22,24mm

FORK ROD HOLDING CLIP 10/12/12.5

FORK OIL LEVEL TOOL-PRO

FORK PRELOAD SOCKET 14mm

FORK PRELOAD SOCKET 17mm

REBOUND P-RING COMPRESSOR-WP 23/28

FORK SEAL INSTALLATION BAGS (5)

FORK SPRING COMPRESSOR PORTABLE

FORK SPRING COMPRESSOR FOOT OPERATED

FORK SPRING COMPRESSOR ADAPTER H-D

FORK SEAL DRIVER 30mm

FORK SEAL DRIVER 33mm

FORK SEAL DRIVER 35mm

FORK SEAL DRIVER 36/37mm

FORK SEAL DRIVER 38/39mm

FORK SEAL DRIVER 40/41 mm

FORK SEAL DRIVER 43mm

FORK SEAL DRIVER 45/46mm

FORK SEAL DRIVER 47/48mm

FORK SEAL DRIVER 49/50mm

SHAFT HOLD TOOL 10,12,12.5,14

SHAFT HOLDING TOOL 14,16,18mm

SHAFT HOLDING TOOL 20,24,29mm

SHAFT HOLDING TOOL 32,35mm

Item Number

TFSH S500

TITT01

TMDB 08

TMPS 01

TMPS 02

TMPS P01P

TMPS P02P

TMVJ 065

TSBD SET

TSCA01

TSCA 19

TSCA21

TSCA 24

TSCP 01

TSCT 01

TSNC 02

TSNG 02

TSNH 48

TSNN01

TSNR 01

TSPA 01

TSPS 1524

TSPS T1524

TSPS T16530

TSPS T20

TSRC 01

TSSB 125

TSSB 14

TSSB 16

TSSB 18

TSSB 1812

TSSC 01

TSSC 02

TSSM01

TSSS 01

TSSS 01S

TSSS 02

TSSS 03

TSVM 01

TTHS 02

TTHS 03

TTHS 13

Description

SHAFT HOLD TOOL 1 /2"

FORK TUBE DISASSEMBLY TOOL

DEBURRING TOOL

PIN SPANNER 4.0 & 4.5mm

PIN SPANNER 5.0 & 5.5mm

SPANNER PINS 4.0 & 4.5 PAIR

SPANNER PINS 5.0 & 5.5 PAIR

VISE JAW SET

BUSH DRIVER SET 12.5,14, 16,18

SHK COMP ADJ SOCKET YZ

SHK COMP ADJ SOCKET 19mm

SHK COMP ADJ SOCKET 21 mm

SHK COMP ADJ SOCKET 24mm

SHOCK CLIP PICK TOOL

RESERVOIR CAP REMOVAL TOOL

NITROGEN CHARGING TOOL - WP

SHOCK NITROGEN GAUGE-PRO

NITROGEN HOSE 48" -HI PRESSURE

SHOCK NITROGEN NEEDLE

SHOCK NITROGEN REGULATOR

SHOCK PRELOAD ADJUSTING TOOL

SHOCK NEEDLE TOOL-WP PDS 1.5x24d

SHOCK NEEDLETOOL-PDS PRO 1.5x24d

SHOCK NEEDLE TOOL-PDS PRO 1.6x30d

SHOCK NEEDLE TOOL-PDS PRO 20-2009

SHOCK RES CAP SETIING TOOL YZ

SHOCK SEAL BULLET 12.5x10mm

SHOCK SEAL BULLET TOOL 14x12mm

SHOCK SEAL BULLET TOOL 16x12mm

SHOCK SEAL BULLET TOOL 18x16mm

SHOCK SEAL BULLET TOOL 18x12mm

SHOCK SPRING COMPRESSOR-LEVER TYPE

SHOCK SPRING COMPRESSOR-SCREW TYPE

SAGMASTER TOOL

SHOCK SEAL HEAD SET TOOL 40-50mm

SHOCK SEAL SET TOOL 40-50mm SHORT

SHOCK SEAL HEAD SET TOOL WP 50mm

SHOCK SEAL HEAD SET TOOL 33-36mm

SHOCK VACUUM FILL TOOL

T-HANDLE SET 8,10,12,14,17mm

T-HANDLE SET8,10,12,13,14,17mm

T-HANDLE 13mm ONLY

251

~ "ti m z 0 x (J1

Appendix 6

RESOURCES

G.M.D. Computrack www.gmd-computrack.com chassis geometry and alignment

lntercomp www.incercomp-racing.com

spring cescers

K & L Supply www.klsupply.com lifcs, scands, rools - dealers only

Lee Parks Design www.leeparksdesign.com bike stands, gloves and accessories

Ohlins Suspension www.ohlins.com suspension components

Penske www.penskeshocks.com suspens ion components

Pit Bull www.pic-bull.com stands

252

Race Tech www.racerech.com

suspensio n components, valving kics, cools, seminars

Roehrig www.roehrigengineering.com

shock dynos

Scotts Performance www.scorcsperformance.com steering dampers

Tony Foale www.ronyfoale.com chassis design

Total Control www.rocalconcrolcraining.nec Lee Parks' Toca! Contro l Riding Courses

WP Suspension www.wpsuspension .com suspensio n produces

WPC Treatment Co, Inc. www. wpccrea cm en r.com friction reduction surface treatment

Index

24 H ours of Montjuich, 94

acceleration, 89 additive damping, 71-72 air

as a spring level, 14 as an o il level, 14

air springs, 6 anti-squat , 86-93 Aprilia Team, 83 Atkins, Darryl, 83

Bayle, Jean Michele, 80 bench vise, I 09 bleeding cool, I 09-110 bottoming, 97

Carlson, Benny, 83 cartridge fork mid-valves, 50-56 cartridge holding tool, I 09 cavitation, 57- 61, 70 clip tool, 111 coatings, 80-8 1 compression damping, 35-36, 43

curves, 40 force, 71 testing, 36-37 too little, 97 too much , 97

compression valve, 48 compression velocity, 27 Condor, 21, I 09 Craftsman, 109

damping, 26, 28 curve, 29, 45, 70 extremes, 95-97 force, 8 measuring, 28-32 velocity, 29

damping rod anatomy, 37 compression stroke, 38-40 fo rks (orifice damping) , 37, 39,

114-126 rebound stroke, 40-41

DeCarbon reservoir shocks, 62 DeCarbon, Dr. C hristian Boucier, 63 dive , 36 drivers, 110

Dymond, M icky, 83 dynamic fr iction, 78-80 dyna mic geometry, 19 dynamic ride height, 19

emulato r, 44, 46-47, 72 emulsion, 62

shocks, 61, 196-225 energy, 8, 26 external top-out spring, 24

fade, 70 Foale, Tony, 85 force, 79-80

rotation, 88 vecto rs, 78

fo rce-deflection curve, I 0 forks

bounces, I 02 chatte rs, 98-99, 101- 102 deflects, I 02 designs, 6 1 dives under breaking, 99 doesn't turn, 98 dynamics, 79 feels loose, 99 front tire wear, 103 gold valve kits, 64 headshakes, I 0 I leaky seals, I 02 loose steering, 98-99 oil level, 110 poor traction, 97-98 power steering, 98-99 pushes, 98-99 runs wide, 98-99 sliding bushings, 79 soft, 97 spring compressor, 11 2 sticky, 100 stiff, 97 troubleshooting, 97-103 tucks, 98-99 wo n't turn well, 99

free sag, 2 1-22 freeloaded stacks, 7 4 friction fo rce, 8 front end trail, increase, 93

geometry measurement, 93 tuning, 93-94

GM O Computrack, 93 gold valve, 68, 72-73

cartridge emulator, 35, 11 4, 120, 124, 138

fo rk, 43-45 installation, 127-155 kits, 61

graduated cyli nder, 110 ground trail, 84

harshness, 97 H ay, Terry, 68 head setting cool, 111

in ternal top-out spring, 24 International Organization fo r

Standardization (ISO), 26

jack, 108 James, Jamie, 45

K&L, 109 Kawasaki , 61 KTM, 60, 66, 83 KYB, 70

lowering, 238

Marzocchi, 61 mechanical springs, 6 metering needle, 68, 112 mid-valve components, 55-58 mid-valve compression stroke, 56-57 Moto Guzzi, 30 Motorcycle Handling and Chassis

Design, 85 multi-stage damping, SO

needle pin tool, 111 nitrogen charging

station, 110 tool, 11 0-111

nitrogen gauge, 110 needle, 111 regu lator, 110

253

O hlins, 63, 66, 226 sag, 22, 25 steering dam per, 63, 65 tools, 111 measurements, 2 1 Stewart, James, 86

oil level tool, 110 set ting, 23 stitctio n zone, 22-23 oil viscosity, 26 straight stacks, 7 4 orifice damping, see damping rod, Sag Master, I 11-11 2 surface

forks Saybolr Universal Seconds (SUS) , 26 roughness, 77 orifice style valving, 7 1 Saybolr, Edward , 26 treatment, 8 1 0-ring, 70 Scott's, 65 suspension

screwdrivers, I 09 oil, 26-28 packing, 95 Seconds Saybolr Universal (SSU), 26 sag, 18- 19 Park Tool, I 09 sel f-correc ting torque, 82 Suzuki, 61, 64 parts cleaner, 11 0 shocks swingarm length, 239 peak rebound velocity, 31 adjusters, 62 pin spanner, 111-112 blown shock bladder, I 05 rape red stacks, 7 4 piston valving style, 71- 74 bottoms, 103 telescopic needle, 69 Pit Bull, 109 clip tool, 111 resting procedure, I 06-107 plushness, 32 design, 6 1- 66 thick shims, 74- 75 pogoing, 95 dynos, 30 thin shims, 74- 75 polishing, 81 feels loose, 104 through-shaft shocks, 62, 66 position, 26 kicks, 103 trac tion, 32 position-sensitive damping system, not tracking, I 05 trail, 83-84, 86-87

66-69 poor traction, I 04 troubleshooting, 97-105 preload , 18-20, 22, 25 preload testing tool, I 11 forks, 97-103

external opt-out, 23 squats on acceleration, I 05 shocks, 103-105 internal opt-out, 23 sticky, I 05 ruck, 98 relaxed, 24 swaps dirt, 103-104 twin-chamber setting, 23- 24 treatment, 68 design, 60

tool, 11 2 valving components, 64 fo rks, 57-61, 156-195 preloaded stacks, 73-74 ShockClock, 19, 30 , 111 twin- tube shocks, 6 1 pressurized forks, 57-6 1 Showa,58-59,6 1, 70 two-stage valving, 72-73 progressive, 41 -43 SI System, 26

damping system shocks, 226- 237 single-style valving, 7 1 unsprung mass, 6-7 shock springs, 68 sockets, 109

push, 98 solid-piston shocks, 62-66 valving styles, 71-76 springs veloci ry, 2 6

rake, 85 compressor, 109 viscosity index, 27-28 ratchets, 109 design, 14- 16 reactive spring series, 24 displacement, 9 weight bias, 94 real trail, 84-86 force, 7, 9, 13, 17 WP, 60, 65, 68, 226 rear anti-squat, increase, 93-94 manufacture, 14-16 WPC,8 1 rear wheel trail , 86 preload , 16-19 wrenches, 109 rebound adjusters, 65 rate9-12, 15 rebound damping, 32-34, 47, 50, 96 measu ring, 15-16 Yamaha, 30, 6 1, 80

adjuster, 30 test, 16-17 testing, 34-35 sprung mass, 6-7, 95 zero offset trail, 83 too little, 95 stack height, setting proper, 173 too much, 95 stacking springs, 12-14

rebound gold valves, 56 standard cartridge forks, 49-50, >< rebound separa tor valve, 75-76 52-55, 127 UJ c

rebound stroke, 42 stands, I 08-109 :!!: rebound valve, 48 static friction, 77-79 reservoir cap remover tool, 111 static sag, measu ring, 20-2 1

254

WORKSHOP

The Best Tools for the Job . ....... , ....... , ••••• ••• ....... ,

Sheet Metal Fabrication

101 Harley-Davidson Evolution Performance Projects N-

How To Rebuild Corvette Rolling Chassis 1963-1982

How to Paint Your Car

How to Paint Your Car 136261 AP • 978-0-7603-1 583-5

How to Paint Flames 137414AP • 978-0-7603-1824-9

How to Master Airbrush Painting Techniques

140458AP • 978-0-7603-2399-1

How to Repair Your Car 139920AP • 978-0-7603-2273-4

How to Diagnose and Repair Automotive

Electrical Systems 138716AP • 978-0-7603-2099-0

Chevrolet Small-Block V-8 ID Guide

122728AP • 978-0-7603-01 75-3

How to Restore and Customize Auto

Upholstery and Interiors 138661AP • 978-0-7603-2043-3

Sheet Metal Fabrication

144207 AP • 978-0-7603-2794-4

Other Great Books in This Series

101 Performance Projects For Your BMW 3 Series 1982-2000

143386AP • 978-0-7603-2695-4

Honda CRF Performance Handbook 140448AP • 978-0-7603-2409-7

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Mazda Miata MX-5 Find It. Fix It. Trick It.

144205AP • 978-0-7603-2792-0

Four-Wheeler's Bible 135120AP • 978-0-7603-1056-4

How to Build a Hot Rod 135773AP • 978-0-7603-1304-6

How to Restore Your Collector Car 2nd Edition 3541-3 145823

128080AP • 978-0-7603-0592-8

101 Projects for Your Corvette 1984-1996

136314AP • 978-0-7603-1461 -6

How to Rebuild Corvette Rolling Chassis 1 963-1982

144467 AP• 978-0-7603-3014-2

Visit www.motorbooks.com

How to Restore Your Motorcycle 130002AP • 978-0-7603-0681 -9

1 01 Sportbike Performance Projects

135742AP • 978-0-7603-1331-2

How to Restore and Maintain Your Vespa Motorscooter

1 28936AP • 978-0-7603-0623-9

How to Build a Pro Streetbike 140440AP • 978-0-7603-2450-9

101 Harley-Davidson Evolution Performance Projects

139849AP • 978-0-7603-2085-3

1 01 Harley-Davidson Twin Cam Performance Projects

136265AP • 978-0-7603-1639-9

Harley-Davidson Sportster Performance Handbook,

3rd Edition 140293AP • 978-0-7603-2353-3

Motorcycle Electrical Systems Troubleshooting and Repair

144121 AP • 978-0-7603-2716-6

Fi rst published in 20 10 by Motorbooks, an imprint of M BI Publishing Company, 400 Fi rst Avenue North, Suite 300, M inneapolis, MN 55401 USA

Copyright © 2010 by Paul Thede and Lee Parks

All rights reserved . With the exception of quoting brief passages for the purposes of review, no part of this publication may be reproduced withou t prio r written permission from the Publisher.

The information in this book is true and complete to the best of our knowledge. All recommendations are made without any guarantee o n the part of the author or Publisher, who also disclaim any liability incurred in connection with the use of this data or specific details.

"Race Tech," "Gold Valve," "Emulator," and other trademarked

Race Tech products used by permission of Race Tech.

We recognize, fu rther, that some words, model names,

and designations mentioned herein are the property of th e trademark holder. We use them for identification purposes only. T his is not an official publication .

Motorbooks tides are also available at discounts in bulk

quantity for industrial or sales-promotional use. For details wri te to Special Sales Manager at MB! Pub lishing Company, 400 First Avenue North, Suite 300, Minneapolis, MN

55401 USA.

To find out more about our books, join us online at www.motorbooks.com.

Digital edition: 978-1-6105-9 166-9

Softcover edition: 978-0-7603-3140-8

ISBN-1 3: 978-0-7603-3 140-8

President/CEO: Ken Fund Publisher: Zack Miller Senior Editor: Darwin Holmstrom Editor: Peter Bodensteiner C reative Director: Michele Lanci-Altomare Design Managers: Brad Springer, Jon Simpson, James Kegley Designer: Danielle Smith

Printed in C hina

SUSPENSION BASICS

SPRINGS

DAMPING

FRICTION

GEOMETRY

TROUBLESHOOTING ANO TESTING

TOOLS ANO EQUIPMENT FOR SUSPENSION SERVICE

SUSPENSION SERVICE DEPARTMENT

Visit motorbooks.com Printed in China

Race Tech's Motorcycle Suspension Bible

BASED ON THE WILDLY popular Race Tech Suspension

Seminars taught by Paul Thede

around the world, this step-by-step

guide shows riders how to make

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Thede gives the lowdown on all types

of suspension, including cartridge

and non-cartridge forks as well

as dual-chamber and nitrogen­

charged shocks. The three forces of

suspension, testing procedures, even

the black arts of chassis geometry:

Thede explains it all. The book

provides step-by-step photos of suspension

disassembly and assembly as well as a

detailed troubleshooting guide for dirt, street,

and track. Race Tech's Motorcycle Suspension

Bible provides a solution to virtually any

handling problem.

$34.99 us £22.50 UK $38.99 CAN

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, ~jl~~jljl IJllJllll lll~lf l~lill MBI Item # 144400