School of Engineering Faculty of Engineering, Physical Sciences and Architecture THE UNIVERSITY OF QUEENSLAND Bachelor of Engineering Thesis Formula SAE Suspension Design Student Name: DANIEL RAYMOND BURT Course Code: MECH4500 Supervisor: Dr. Ross McAree Submission date: 7 th November 2003 A thesis submitted in partial fulfillment of the requirements of the Bachelor of Engineering degree program in the Division of Mechanical Engineering
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School of Engineering
Faculty of Engineering, Physical Sciences and Architecture
THE UNIVERSITY OF QUEENSLAND
Bachelor of Engineering Thesis
Formula SAE Suspension Design
Student Name: DANIEL RAYMOND BURT Course Code: MECH4500 Supervisor: Dr. Ross McAree Submission date: 7th November 2003
A thesis submitted in partial fulfillment of the requirements of the Bachelor of Engineering degree program in the
Division of Mechanical Engineering
Daniel Raymond Burt
62 Ellen St Woody Point
QLD, 4019 7 November 2003 Prof. J. M. Simmons Head of School School of Engineering University of Queensland Brisbane Queensland 4072 Dear Sir, I hereby submit my Thesis titled “Formula SAE Suspension Design” for consideration as partial fulfilment of the Bachelor of Engineering degree. All the work contained within this Thesis is my original work except where otherwise acknowledged. I understand that this thesis may be made publicly available and reproduced by the University of Queensland unless a limited term embargo on publication has been negotiated with a sponsor. Yours sincerely, Daniel Raymond Burt 33628055
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ABSTRACT
Formula SAE is a student project undertaken by the Mechanical Engineering department
of the University of Queensland and various other universities in Australasia, America,
Europe and England. It is a competition to engineer and build a racing car to compete in
design and track events.
The objective of my thesis is to analyse the performance of the 2001 and 2002 formula
SAE racing car of the University of Queensland, identify it’s short comings in terms of
suspension/steering geometry, set up and structural integrity and improve the design for
the 2003 formula SAE.
The thesis follows the format of a design analysis. The investigation and analysis of the
performance of the previous 2 years formula SAE race cars of the University of
Queensland is used as a platform as to the complete redesign of the suspension system of
the 2003 University of Queensland formula SAE race car.
It will discuss the design of the suspension and steering for the 2003 University of
Queensland formula SAE racecar in order to optimise its performance and ability to be
tuned to a particular racing course.
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ACKNOWLEDGEMENTS
I would like to express my appreciation to the following people for their valuable
contribution and assistance in the completion of this thesis:
All fellow UQ Racing team mates from both the 2002 and 2003 teams, for their
dedication, passion and extreme time commitment needed to be a part of this formula
SAE team. In particular, George Commins and Francis Evans for their countless hours of
support and technical advice/ input on the suspension design.
Mr George Dick, for his patience, technical tuition, guidance and dedication to the
formula SAE project throughout the year.
The workshop staff; John, Ross, Dave and Neil, for your technical assistance and
attention to the formula SAE project throughout the year.
Graham for time spent using instron to test rod ends strength and spring rates.
Professor Ross McAree for being my thesis supervisor, and being inspirational in his
systematical approach to all engineering problems.
Professor David Mee for being the academic supervisor of the Formula SAE project in
the University of Queensland.
Professor Hal Gurgenci for making the Formula SAE project available to students at the
University of Queensland.
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CONTENTS
ABSTRACT........................................................................................................................ I
ACKNOWLEDGEMENTS ............................................................................................ II
The Thomas marsh and fox spring rates were close to their designed value. However, the
Risse spring was a lot stiffer than as designed.
6.4.4 X-Ray
The placement of the spring and damper units in the vehicle required that a spherical
bearing be placed in both ends of the damper unit. This presented a major problem as the
bolt needed to secure the damper unit needed to be of adequate size to take the loading
and yet a spherical bearing needed to be sourced that would fit into the tight hole without
too much machining of the damper unit. The spherical bearing chosen was an SKF
GE6C. It allowed a 6 mm high tensile bolt to be used and didn’t require too much
machining for fitment, only 1 mm larger diameter. The machining was not blindly
performed. X-Rays taken in the department of Veterinary Science illustrated just how
close the machining came to interfering with internal passages and mechanical
adjustment components.
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6.5 Steering Selection
On researching steering rack availability of commercial steering racks. It was deemed
economically viable to purchase a BRT steering rack at $400 US for a 750g it wasn’t
even worth cons idering manufacturing a custom one.
Figure 6.14 Steering Rack in 2003 Racecar
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6.6 Accuracy & Adjustment
One of the major considerations in the construction of the 2003 racecar was the accuracy
to which the major components were constructed. Particular care was taken in the chassis
construction to ensure that the suspension attachment points were in exactly, or as close
to as possible, in the place as designed. Even the slightest inaccuracy of 1 mm can move
the roll center by up to 5 mm.
Figure 6.15 Chassis on Jig for suspension Pickup Accuracy
All suspension parameters such as camber, castor, wheel alignment, ride height and toe
can adjusted by the rod end thread tuning. In the case of the ride height and toe
adjustments the pushrod/pullrod and toelink members function as turnbuckles with both a
right and left hand thread rod end a for ease of adjustment on the car.
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Kingpin inclination on this racecar is 0° and is not adjustable. Making the kingpin
inclination adjustable is a difficult task, without compromising the design. In 2001, a rod
end was used on the upper front wishbone connection to the upright. It was consequently
in bending under braking and inevitably yielded during driving. The only other way to
achieve adjustable kingpin inclination is to shim pack a bracket to the connection point of
the upper wishbone. Both options compromise the lightweight, simple and effective
design and therefore, kingpin inclination adjustment was sacrificed.
6.7 Component Placement
The placement of inboard suspension components within the chassis is a difficult task
and some of the main points to consider whilst doing so are:
• Aesthetics of Packaging
• Linearity of movement
• Chassis load paths
6.7.1 Rocker, Spring and Damper and Anti-roll bar Placement
As in previous years the springs and dampers where placed with such a ratio to utilize all
the damper travel. This is to maximize the efficiency of the damper and avoid potential
cavitations. The other main concern of the rocker, spring and damper placement is the
linearity of the movement of the spring compression to upright displacement. It is
impossible to get exactly linear movement, however, close to linear movement can be
achieved. The design methodology for this was to place the spring and damper unit with
respect to the rocker in such a way that at full compression/travel they met at right angles.
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This would mean that the movement would be as close to linear as possible and the
suspension movement would always be getting progressively stiffer rather than softer.
The rear anti-roll bar placement was placed using the same design considerations as the
rocker, spring and damper placement.
Figure 6.16 Front Spring and Damper Placement
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Figure 6.17 Rear Spring/Damper and Anti-roll Bar Placement
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7. VEHICLE SET UP
The racecar set up is just as important as the original design. It is in the set up that all the
inaccuracies introduced in the construction of suspension components can be rectified to
ensure the geometry as the vehicle is designed to have is in fact, the same as the geometry
achieved on the vehicle.
A wheel alignment is the first set up operation that is to be performed on the vehicle.
The University of Queensland’s sponsorship with fulcrum suspensions allows free wheel
alignment time on their wheel aligner. This particular wheel aligner performs laser
measurements through many steering angle operations to determine suspension
alignment.
Through the use of mathematics and some logical thinking, all links that are out in the
alignment of the suspension can be rectified in 1 adjustment iteration. The wheel
alignment is performed by the adjustment of rod end bearings at the end of all members
as discussed in the previous chapter.
Some interesting points to note about this wheel alignment set up are:
• Toe is extremely sensitive and must be adjusted after all changes.
• There are no chassis alignment measurements - chassis alignment to straight
suspension still questionable.
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A well-designed suspension system will have plenty of room for adjustment. The
possibilities for adjustment allowable in this racecar are:
• Ride Height
• Castor
• Camber
• Toe
• Spring Rates
• Rear Anti-roll Bar Rates
• Compression Damping
• Rebound Damping
• Anti-Dive Geometry
• % Ackerman on steering
• Tire Pressure
Each setup change has an effect on all other suspension parameters and this must be
considered whilst setting up the racecar.
For example, a ride height change will change the roll centres; Tire pressure will change
the roll centres; Castor will change the roll centres; spring rates will change anti-roll
rates; even damper adjustment will affect anti-roll rates, however, only in the transient
phase. These are only to name a few of the effects of a few possible changes.
Considering this and the fact that the driver’s style is just as an important and integral
part of the vehicles performance, racecar setup is not an easy task and can be a very
daunting task. It requires a lot of experience and the use of intuition and inference.
Unfortunately, due to the late completion of the racecar this year, not enough time has
been allowed to go into too much detail with the setup of the 2003 university of
Queensland formula SAE racecar as was originally intended with this thesis.
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8. RESULTS
The resulting weight distribution on the racecar was somewhat different to as designed.
The original design was for a weight distribution of 50:50. However, the prediction of the
weight distribution of a racecar that didn’t exist at the time is near impossible. The
resulting weight distribution of 53.5:46.5 front heavy, with a 90 kg driver.
This problem had to be rectified before the racecar could be driven/tested successfully.
The spring rates had to be changed from those original designed for (180 lb front, 225 lb
rear), to 235 lb front and 195 lb rear to achieve similar sprung mass frequencies.
Once this was rectified, extensive testing was undertaken.
The first testing session was conducted immediately following the racecar construction
completion on the 8/10/03. This short testing session revealed a lot of minor problems as
well as toe control issues. This was followed by a complete suspension and drive train
strip and crack test. None of the parts had been damaged or showed crack initiation. A
second and much longer testing session was conducted on 10/10/03.
The 2003 car pulls extremely hard with its spool differential and almost flat torque from
5000 rpm. Its turn in response was amazing, and with no suspension tuning other than a
comprehensive wheel alignment at this stage the results were more than pleasing. The
vehicle wasn’t perfectly balanced, being slightly prone to over steer on power
application. However, at this stage the rear anti-roll bar had not been implemented.
With preliminary testing completed the evaluation of the rear toe control and inevitably
redesign and reconstruction of toe link mounting location and toe link. The testing was
simple and involved the application of a torque to the wheel whilst measuring the
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deflection through use of a wheel-mounted laser. The results of the testing revealed that
toe control was in fact an issue.
Rear Toe Deflection
y = 0.0054x + 0.3192
00.20.40.60.8
11.21.41.61.8
0 50 100 150 200 250
Torque (Nm)
Toe (deg)
Figure 8.1 Rear Toe Deflection
With the steady state cornering torque on the wheel in the order of 100 Nm which relates
to a deflection of almost 1 deg, which is outrageous. The problem or reason for the
excessive deflection was the small moment arm to the toe link from the kingpin of 50
mm. The most suitable solution to this problem was to relocate the toe link further up the
upright and chassis, where a much larger moment could be achieved without clashing.
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Figure 8.2 Toe Control Solution
The implementation of the rear anti-roll bar and fixed rear toe control for a testing session
on the 19/10/03 saw a dramatic improvement in the cornering ability of the racecar.
The performance of the 2003 formula SAE racecar is astounding. In comparison to the
2001/2002 racecar it is in another league altogether. With myself as driver skid pad
testing was undertaken. The racecar was setup as it would be in competition, however,
with formula ford tires instead of Hoosier slicks. The skid pad was of an inside diameter
of 15.25 m as in the competition, however, on undulating off camber asphalt. Consistent
times of 5.7s a lap were achieved. Evaluation of the average lateral acceleration for this
yielded a result of 0.99 g’s. Considering that the formula ford tires are no where near as
soft a compound as the Hoosier R25A compound tires as used in previous years and to be
used in this years competition, and that with the Hoosier tires the 2002 racecar achieved a
maximum of 1.14 g’s, as seen in Riseley [6], the resulting performance is going to be
very interesting when the Hoosier R25A compound tires are used.
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The vehicle appears to be performing as designed, sometimes elevating the rear inside
wheel on corner entry. The camber of all wheels seem to be optimal with tire
temperatures, as monitored in the pits, a consistent 41°C across the front tires and 43 °C
across the rear.
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9. CONCLUSIONS & RECOMMENDATIONS
In conclusion, the 2003 formula SAE racecar has proven to be quite successful so far in
testing. The team spirits are high for the upcoming competition with many testing days
scheduled in the month left before the competition.
With regard to the outcome of the suspension design, the results so far look promising
and so far the design is quite successful. There is no right or wrong answer in suspension
design. All suspension parameters have a unique relationship with all the others and as
such they must be addressed as a complete suspension package. With more time tuning
these suspension parameter the car will hopefully go on to be competitive at the formula
SAE competition in Adelaide on the 4th to 7th of December this year.
In all honestly, the successful use of data acquisition systems on racing cars is difficult to
achieve. Measuring the shock position is good for calculating wheel weights and
developing shock speed histograms for shock setup. Tire temperature sensors can tell if
the tires are cambered excessively or over/under inflated. Strain gauges on the suspension
members can help evaluate the shock and bump loading of the member as well as
possibly evaluated fatigue loading frequencies for component design.
Other than this, the evaluation of other parameters with data acquisition is of not such a
straightforward manner.
I guess the point is that the problem is not only in how do you achieve accurate
measurement of other parameters, but also what changes should be made upon knowing
such information.
For example, if optical slip angle sensors were to be used in the future, they can only be
used for academic purposes, considering it’s already known that pro Ackerman works
best on formula SAE cars. The result will tell you that you should be running around 70%
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Ackerman for best performance in the steady state. So the point being why measure it if
it’s not going to prompt a setup change in the car, or achieve anything towards the cars
performance.
The driver is just as much an integral part of the cars performance as the car itself and
must be treated as such. Often driver feedback is a lot more useful than any data ever
could be.
The use of the program suspension analyzer has some potential problems. It does not take
into account tire deformation whilst simulating vehicle steady state dynamics. The static
deformation of tire can be compensated for, however, a certain degree of inaccuracy is
introduced in the roll center, camber analysis without considering the change in tire
deformation in the various dynamic situations being modeled.
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10. BIBLIOGRAPHY
1. Gillespie, T.D.,1992, Fundamentals of Vehicle Dynamics, Society of Automotive
Engineers, Warrendale, Pa.
2. Juvinal, R.C., Marshek, K.M., 2000, Fundamentals of Machine Component
Design (3rd Edition), New York, John Wiley and Sons.
3. Manhire, O., 2001, Suspension Geometry Design of the 2001 University of
Queensland Formula SAE Racecar, BE thesis, University of Queensland.
4. Maria, P., 2001, Suspension Component Design for Formula SAE, BE thesis,
University of Queens land.
5. Milliken, W.F and Milliken, D.L., 1995, Racecar Vehicle Dynamics, Society of
Automotive Engineers, Warrendale, Pa. USA
6. Riseley, C., 2002, Suspension Optimisation of the 2001 University of Queensland
Formula SAE Racecar, BE thesis, University of Que ensland.
7. Smith C., 1996, Drive to Win , Carroll Smith Consulting Inc, Palos Verdes Estates,
Ca USA.
8. Smith C., 1978, Tune to Win , Aero Publishers Inc, Fallbrook, Ca USA.
9. Smith C., 1975, Prepare to Win , Aero Publishers Inc, Fallbrook, Ca USA.
10. 2003, Hoosier Racing Tires Homepage, [Online], <www.hoosiertire.com>,
[Accessed January 15 2003]
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APPENDIX A
FSAE-A Design Spec Sheet 2003 Competitors: Please replace the sample specification values in the table below with those appropriate for your vehicle and submit this to with your design report. This information will be reviewed by the design judges and may be referred to during the event. --Please do not modify format of this sheet. Common formatting will help keep the judges happy! --The sample value s are fictional and may not represent appropriate design specs. --Submitted data will NOT be made public or shared with other teams.
Car No 41
University University of Queensland
Dimensions Front Rear
Overall Length, Width, Height
Wheelbase 1525 mm
Track 1200 mm 1100 mm
Weight with 68 kg driver 154 kg 154 kg
Suspension Parameters Front Rear
Suspension Type Unequal length A-Arms. Pull rod actuated spring/damper unit
Unequal length A-Arms. Push rod actuated spring/damper unit.
Tyre Size and Compound Type 20.7x6-13 Hoosier R25A 20.7x6-13 Hoosier R25A Wheels 3 Pce, Mag Centre
13"x6"-43mm o/s 3 Pce, Mag Centre 13"x6"-43mm o/s
Design ride height (chassis to ground)
40 mm 40 mm
Center of Gravity Design Height 300 mm above ground Suspension design travel 26 mm jounce/ 26 mm
rebound 26 mm jounce/ 26 mm rebound
Wheel rate 19.5 N/mm 25.4 N/mm Roll rate 0.86° / g, without anti-roll bars Sprung mass natural frequency (in vertical direction)
2.76 HZ 3.15 Hz
Jounce Damping 90% of critical damping @ 30mm/sec
56% of critical damping @ 30mm/sec
Rebound Damping 62% of critical damping @ 30mm/sec
54% of critical damping @ 30mm/sec
Motion ratio 0.9:1 0.96:1 Camber coefficient in bump 0.5° / 10 mm bump 0.6° / 10 mm bump
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Camber coefficient in roll 0.42°/g 0.38°/g Static Toe and adjustment method 0mm toe out adj. by tie
rods 0mm toe in adj. by toe links
Static camber and adjustment method
0° by inboard rod ends 0° by inboard rod ends
Front Caster and adjustment method
7° adjustable by rod ends
Front Kingpin Axis 0° non-adjustable Kingpin offset and trail 30 mm offset, 32 mm
trail
Static Ackerman and adjustment method
100% Ackerman @4.8m turn diameter Adjustment by interchangable steering link arms
Anti dive / Anti Squat AD 10% @ 1.5 g's, adjustable by spacers ( 0%-10% )
0% (parallel)
Roll center position static 35 mm above ground, CL of the car
38 mm above ground, CL of the car
Roll center position at 1g lateral acceleration
35 mm above ground, moves 6.35 mm toward inner wheel (with no steer), central with 15m turn diameter, 6.35mm toward outer wheel with 7m turn diameter
38 mm above ground, moves 2.8 mm toward outer wheel
Steering System location Rear steer, not in line with lower A-arm, yet no bump steer
Frame Construction Steel tube space frame with bonded aluminium panels Material 4130 Chrome Moly tube Joining method and material TIG welded, 100% MPI to AS 1554.5 SP Targets (Torsional Stiffness or other)
Torsional stiffness and validation method
Bare frame weight with brackets and paint
Crush zone material Crush zone length Crush zone energy capacity
Powertrain
Manufacture and Model 1998 Honda CBR600 F3 4 cylinder, custom dry sump, with integral scavenge pump.
Displacement 599 cc Fuel Type Optimax Induction Atmospheric induction Max Power design RPM 10,000 rpm. 56.5Kw (76Hp) Max Torque design RPM 9,000 rpm. 57Nm (42ft.lbs) Min RPM for 80% max torque 5,850 rpm Effective Intake Runner Length 308 mm. 35mm ID. Effective Exhaust runner length 690 mm Primary, 31.8 mm ID. 185mm Secondary,
44.4mm ID . Exhaust header design 4-2-1 equal length, Fuel System (manf'r) Student designed/built fuel injection, sequential Fuel System Sensors IAT, CTS, CPS, TPS, EGO Injector location Above ports and pointing at back of inlet valves Intake Plenum volume 1575 cc (Butterfl y to airhorns). "Symetric" Plenum-
Runners. Compression ratio 12.0 :1 Fuel Pressure 3 bar (static), EV1, 150g/min injectors Ignition Timing MoTec M4 Coolant System and Radiator location
(2) Side pod mounted radiators, with electric fans, and water pum ps.
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Fuel Tank Location, Type Floor mounted aluminum tank between seat and firewall Muffler Carbon fibre canister.
Drivetrain
Drive Type Chain #520 Differential Type Spool Diff Final Drive Ratio 4.00 (13:52) Vehicle Speed @ max power (design) rpm
1st 45 km/h 2nd 65 km/h 3rd 81 km/h 4th 97 km/h 5th 111 km/h 6th 123 km/h Half shaft size and material GKN 21mm OD Joint type GKN Aerodynamics (if applicable)
Front Wing (lift/drag coef., material, weight)
N/A
Rear Wing (lift/drag coef., material, weight)
N/A
Undertray (downforce/speed) N/A
Wing mounting N/A
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APPENDIX B
Roll Centre Analysis
Front Geometry in Suspension Analyzer
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Front Camber Gain with 1° of roll (All measurements are in degrees)
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Front Camber Gain with 1” of dive
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Rear Geometry in Suspension Analyzer
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Rear Camber Gain with 1° of roll (All measurements are in degrees)
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