PROGRESS IN TIRES FHWA Workshop 25 Oct 2007

PROGRESS IN TIRES FHWA Workshop 25 Oct 2007 John Melson Michelin Americas R&D

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 hit the 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 © Michelin Tire Corporation 2

Early days: Rough roads Rigid wheel no tire: the wheel is forced to mount the obstacle and then drop Rigid wheel response Tire with high inflation pressure Wheel with tire: the tire deforms over the obstacle, less vertical motion, more energy recoverd 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. © Michelin Tire Corporation 3

Membrane Equilibrium Shape Nφ φ NΘ Θ r Radius of curvature is determined by BIAS CASING Curvature and casing cord length determine shape Shape of casing + mechanical properties of casing section determine footprint/contact pressures and thus performance in wear, traction, © Michelin Tire Corporation 4

Bias Construction Parameters and Inflated Shape r r 0 Building on drum Bias Angle H/W 90 105 42 85 32 80 28 75 24 65 Conformed to larger radius ply angles decrease Rolling direction Contact Patch progression High H/W to Low H/W © Michelin Tire Corporation 5

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 stress distribution bad, cornering stiffness is very low • Shearing between plies in sidewall where large deformation imposes high displacements between cables which are close to each other. • Cord paths (except for radial) are non – geodesic with normal building 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 © Michelin Tire Corporation 6

BELTED RADIAL CONSTRUCTION, LOAD BEARING STRUCTURES NΘ/Nφ parameter Crown Belt to Carcass Shear φ, p Rφ large Crown Belts (2) Casing Ply (900) Nφ NΘ Rφ small r © Michelin Tire Corporation Shear Coupling ≈ Bead Wire 7

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 © Michelin Tire Corporation 8

Typical Radial Contact Stresses Radial construction can distribute normal stresses more evenly. Allows tuning of tangential stresses to improve abnormal wear resistance © Michelin Tire Corporation 9

Tire Treads and Tread Compounds have evolved rapidly • Tread patterns and compounds needed to deal with wet traction and soft soil conditions. • Wear forms and wear rate must be optimized • Tread compounds and mechanics interact – the most effective designs optimize the two together • The casing evolves slowly, the tread evolves rapidly • Customer perception important – if it doesn’t look “traction” it hasn’t got traction. © Michelin Tire Corporation 10

A recent tread innovation example: Using interlocking sipes to modify contact stresses © Michelin Tire Corporation 11

Another major change: Rims and Wheels & Tires Truck Rims: Sealing Pressure Casing Tension Tube Type/Flat Seat/Multipiece: Rim flange removable, rim pieces locked in place by tire pressure and mechanical engagement. Subject to explosive failure throwing metal pieces. Tube increases tire running temperature Rim Load 150 slope 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. © Michelin Tire Corporation 12

Truck tire naming by epoch Tube Type Bias Ply Tires – almost always on multi-piece rims 10. 00 -20/22/24 XXX Tire width in inches(10, 11, 12. . ) Tire type – usually a tread name Rim Diameter even integers 20, 22, 24 = tube type multi-piece rim 10. 00 R 20/22/24 XXX R =Radial (different load/pressure) Tubeless Tires – almost always on single piece rims (150 drop center for truck) Rim Diameter half inch sizes 11 R 22. 5 / 24. 5 XXX Tires were ~ 90 series Tire width in inches(10, 11, 12. . ) no decimal Most recently metric width and aspect ratio added Tire Section Height/Width 275/80 R 22. 5 / 24. 5 XXX © Michelin Tire Corporation 13

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 when 70 < H/W < 90. • Low H/W in belted construction pushed towards higher inflation pressures to control endurance side effects -> greater contact stress level, less even stress distribution in contact. © Michelin Tire Corporation 14

The answer: Circumferential reinforcement Rφ -> ∞ Circumferential (00) reinforcing Increase width, lower H/W A 445/50 R 22. 5 casing 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 © Michelin Tire Corporation 15

Rolling Resistance Evolution 1910 - 2002 Rolling Resistance (10 -3) Bandage plein 30 First tires 25 20 15 10 First cable reinforced tires Truck Tire Green X Energy 3 Energy Xone First Metalique Tires 5 0 1880 Pass Tire First Radial tires 1900 1920 1940 1960 1980 2000 Railroad wheel Metro/subway tire Research materials (Shell eco marathon) 2020 Order of magnitude in 2002 : - Passenger car : 8, 5 -13 x 10 -3 - Truck Tires : 4, 5 (Xone) - 10 x 10 -3 - Motorcycle : 2, 5 - 5 x 10 -3 © Michelin Tire Corporation 16

Rolling Resistance Behavior: α, β Determined by combination of mechanical effects of tread and casing behavior. Rubber Compounds vary magnitude of R 0 at P 0 and Fz 0 α~ -0. 2 β~ -0. 1 for a dual truck tire at road velocities Xone/duals R/R 0 Fz/Fz 0 P/P 0 RR behavior: pressure effect is strong, Load effect weaker © Michelin Tire Corporation 17

Center Reinforced Low H/W (Xone) Design Goals • Equivalent vehicle handling (braking, acceleration, cornering, stability) in all situations. • • Better optimization of vehicle gross weight/volume, wear, rolling resistance and endurance than 80 H/W tire & rim = lower cost of ownership Equal operating temperature (short term endurance) Modified axle shown -> better roll over Standard axle + 2” off set wheel -> equal roll over © Michelin Tire Corporation 18

What customers want • Safety – Vehicle stability – stopping, cornering, emergency maneuvers © Michelin Tire Corporation 19

What customers want • Life cycle cost minimized – – – Purchase cost Wear life Fuel consumption Payload maximization Maintenance Vehicle down time • Pressure maintenance • Repairability / Retreadability © Michelin Tire Corporation 20

Behind the evolutions Enabling material technologies Vulcanization Sulfur linking of rubber polymer chains Carbon Black (“Early nanoparticle technology”) Further reinforcement of rubber – tuning of compound viscoelasticity, abrasion resistance Synthetic rubbers, natural and synthetic blends More rubber properties tuning possibilities Rubber/brass bonding Structural bond needed to make a belted radial possible, brass plated steel + special rubber mix provides high quality bond Silica Used with or in place of carbon black-new adherence/wear/rolling resistance trade off Open steel cable constructions Permits 00 reinforcing in crown without cable rupture © Michelin Tire Corporation 21