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PROGRESS IN TIRES
FHWA Workshop
25 Oct 2007
John Melson
Michelin Americas R&D
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Topics
In the beginning rough roads and early tires The bias tire, how it works, and how it led to
The radial tire
Truck tires and how they perform- why radials hitthe sweet spot for modern vehicles and roads
Why low aspect ratio radial tires are difficult
The new hybrid and how it advances design one
step further
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Rigid wheel no tire: the wheel is forced to
mount the obstacle and then drop
Wheel with tire: the tire deforms over the
obstacle, less vertical motion, more energyrecoverd
Early days: Rough roads
Rigid wheel response
Tire with high
inflation pressure
Tire with low
inflation pressure
A 1888 patent by J.B. Dunlop described how a
pneumatic tube attached to a rigid rim could ease
rolling over rough ground significantly.
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Membrane Equilibrium Shape
RADIUS&ANGLEPOSEBIAS
0
222
0
2222
RADIAL
22)(cos
)(cos221
)cos(
cp
ep
ec rr
rrr
rr
r
R
pR
N
r
N
Radius of curvature is determined
by
N
N
Curvature and casing cord length determine shapeShape of casing + mechanical properties of casing section
determine footprint/contact pressures and thus
performance in wear, traction,
r
BIAS CASING
N
N
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Building
on drum Conformed to largerradius
ply angles decrease
Bias Construction Parameters and Inflated Shape
BiasAngle
H/W
90 105
42 85
32 80
28 75
24 65
r0r
Rolling direction
Contact Patch progression
High H/W to Low H/W
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Bias Casing Properties
Simple construction, many reinforcing materials can be used Lower bias angles provide higher cornering stiffness because more
of the length of the casing is involved in steering or braking
Pure radial has poor performance contact patch shape / contact stressdistribution bad, cornering stiffness is very low
Shearing between plies in sidewall where large deformationimposes high displacements between cables which are close toeach other.
Cord paths (except for radial) are non geodesic with normalbuilding methods so static shears between plies are induced with
inflation Contact area shape and stress are largely determined by bias angle.
Some level of adjustment can be made by varying rubber thickness
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Crown Belts (2)
Casing Ply (900)
Shear Coupling
Bead Wirer
, p
BELTED RADIAL CONSTRUCTION, LOAD BEARING STRUCTURES
Y
-1.00
-0.50
0.00
0.50
1.00
-1.00 -0.50 0.00 0.50 1.00
Crown Belt to Carcass Shear
N/N parameter
R large
R small
pR
N
r
N
)cos(
NN
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Radial Casing Properties
Flat crown, flexible sidewall
Geodesic casing -> less fatigue, lower rolling losses
Casing shape has more design parameters variability
better contact area shape, better contact stress distribution
better wear life, traction, rolling losses
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Typical Radial Contact
Stresses
Radial construction can
distribute normal stresses
more evenly.
Allows tuning of tangential
stresses to improve abnormal
wear resistance
Stress measurements on shoulder block of dual tire
-4
-2
0
2
4
6
8
10
-150-100-50050100150
Position, mm
Stress,
bar(daN/cm2)
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Tire Treads and Tread Compoundshave evolved rapidly
Tread patterns and compounds needed to deal withwet traction and soft soil conditions.
Wear forms and wear rate must be optimized
Tread compounds and mechanics interact the mosteffective designs optimize the two together
The casing evolves slowly, the tread evolves rapidly
Customer perception importantif it doesnt look
traction it hasnt got traction.
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A recent tread innovation example:
Using interlocking sipes to modifycontact stresses
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Truck Rims:Tube Type/Flat Seat/Multipiece:
Rim flange removable, rim pieces locked in
place by tire pressure and mechanicalengagement.
Subject to explosive failure throwing metal
pieces.
Tube increases tire running temperature
Tubeless/150 Drop Center
Single piece rim, casing ply forces provide leverage to seal tire on rim. Lower
operating tire operating temperature, higher bead stresses, low probability of thrown
metal fragments from rim or tire failure.
150 slope
Sealing Pressure
Rim Load
Casing Tension
Another major change: Rims and Wheels & Tires
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Truck tire naming by epochTube Type Bias Ply Tires almost always on multi-piece rims
10.00-20/22/24 XXX
Tire width ininches(10,11, 12..)
Rim Diametereven integers 20,22,24 = tube
type multi-piece rim
Tire type usuallya tread name
10.00R 20/22/24 XXX
R =Radial(different load/pressure)
Tubeless Tires almost always onsingle piece rims (150 drop centerfor truck)
11R22.5 / 24.5 XXX
Tire width ininches(10,11, 12..)
no decimal
Rim Diameterhalf inch sizes
275/80R22.5 / 24.5 XXX
Most recently metric width and aspect ratio added
Tire Section Height/Width
Tires were ~ 90 series
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H/W what limits?
Trucking profits from lower H/W:
Double wide tire (275/80 -> 445/50 or 455/45) NA trucking
Lower diameter tires (315/80 -> 315/60) European evolution
Belted radial constructions have most endurance when70 < H/W < 90.
Low H/W in belted construction pushed towards higherinflation pressures to control endurance side effects ->greater contact stress level, less even stress distribution
in contact.
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Circumferential (00
)reinforcing
Increase width, lower H/W
Height
constant with
respect to dual
equivalent tire
Three way hybrid of radial casing, small angle bias belt at shoulder and circumferential
(00) reinforcing at center
Reduces shear stresses at shoulder -> lower inflation pressure for equal crown
endurance
Better contact stress distribution in wide casing construction
The answer: Circumferential reinforcement
A 445/50R22.5 casing
R ->
p
r
N
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Rolling Resistance (10-3)
First tires
First Radialtires
Green X
Energy 3
Energy
FirstMetalique
Tires
First cablereinforced
tires
30
25
20
15
10
5
0
1880 1900 1920 1940 1960 1980 2000 2020
Bandage plein
Pass Tire
Truck Tire
Railroad wheel
Metro/subway tire
Research materials
(Shell eco marathon)
Order of magnitude in 2002 :
- Passenger car : 8,5 -13 x10-3
- Truck Tires : 4,5 (Xone) - 10 x10-3
- Motorcycle : 2,5 - 5x10-3
Rolling Resistance Evolution 1910 - 2002
Xone
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z
z
x FPK
F
FR
R/R0
Fz/Fz0
P/P0
Rolling Resistance Behavior:
, Determined by combination of mechanical effects
of tread and casing behavior.
Rubber Compounds vary magnitude of R0
at P0
and Fz0
~ -0.2
~ -0.1
for a dual truck tire at road velocities
RR behavior: pressure
effect is strong, Load
effect weaker
Actual Tire Rolling Resistance Ranges - Class 8
0.00
2.00
4.00
6.00
8.00
10.00
12.00
TireRR
t(kg/1000kg)
New tires Recap tires
Steer Drive Trailer
act. bic
XON
act.
act.
bic bic
bic "best in class"
XONXONE
XONE New Wide-baseact. 2000 avg.
Xone/duals
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Center Reinforced Low H/W (Xone)Design Goals
Better optimization of vehicle grossweight/volume, wear, rollingresistance and endurance than 80H/W tire & rim
=
lower cost of ownership Equal operating temperature (short
term endurance)
85
54
66
78
Equivalent vehicle handling(braking, acceleration,
cornering, stability) in all
situations.
Modified axle shown -> better roll over
Standard axle + 2 off set wheel -> equal roll over
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What customers want
Safety
Vehicle stability stopping,cornering, emergencymaneuvers
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What customers want
Life cycle cost minimized Purchase cost
Wear life
Fuel consumption
Payload maximization Maintenance
Vehicle down time
Pressure maintenance
Repairability / Retreadability
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Behind the evolutionsEnabling material technologies
Vulcanization Sulfur linking of rubber polymer chains
Carbon Black (Early
nanoparticle technology)Further reinforcement of rubber tuning ofcompound viscoelasticity, elasticity, abrasionresistance
Synthetic rubbers, naturaland synthetic blends
More rubber properties tuning possibilities
Rubber/brass bonding Structural bond needed to make a belted radialpossible, brass plated steel + special rubber mixprovides high quality bond
Silica Used with or in place of carbon black-newadherence/wear/rolling resistance trade off
Open steel cableconstructions
Permits 00 reinforcing in crown without cablerupture