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

© Michelin Tire Corporation 2 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 3 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 energy recoverd 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.

© Michelin Tire Corporation 4 Membrane Equilibrium Shape Θ φ Radius of curvature is determined by 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, r BIAS CASING NΘNΘ NφNφ

© Michelin Tire Corporation 5 Building on drum Conformed to larger radius ply angles decrease Bias Construction Parameters and Inflated Shape Bias Angle H/W r0r0 r Rolling direction Contact Patch progression High H/W to Low H/W

© Michelin Tire Corporation 6 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 7 Crown Belts (2) Casing Ply (90 0 ) Shear Coupling Bead Wire ≈ r φ, p BELTED RADIAL CONSTRUCTION, LOAD BEARING STRUCTURES Crown Belt to Carcass Shear N Θ /N φ parameter Rφ large Rφ small NΘNΘ NφNφ

© Michelin Tire Corporation 8 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

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 10 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 11 A recent tread innovation example: Using interlocking sipes to modify contact stresses

© Michelin Tire Corporation 12 Truck Rims: 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 Tubeless/15 0 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 slope Sealing Pressure Rim Load Casing Tension Another major change: Rims and Wheels & Tires

Truck tire naming by epoch Tube Type Bias Ply Tires – almost always on multi-piece rims /22/24 XXX Tire width in inches(10,11, 12..) Rim Diameter even integers 20,22,24 = tube type multi-piece rim Tire type – usually a tread name 10.00R 20/22/24 XXX R =Radial (different load/pressure) Tubeless Tires – almost always on single piece rims (15 0 drop center for truck) 11R22.5 / 24.5 XXX Tire width in inches(10,11, 12..) no decimal Rim Diameter half inch sizes 275/80R22.5 / 24.5 XXX Most recently metric width and aspect ratio added Tire Section Height/Width Tires were ~ 90 series

© Michelin Tire Corporation 14 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 15 Circumferential (0 0 ) 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 (0 0 ) 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 Rφ -> ∞

© Michelin Tire Corporation 16 Rolling Resistance (10 -3 ) First tires First Radial tires Green X Energy 3 Energy First Metalique Tires First cable reinforced tires 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 x Truck Tires : 4,5 (Xone) - 10 x Motorcycle : 2,5 - 5x10-3 Rolling Resistance Evolution Xone

© Michelin Tire Corporation 17 R/R 0 F z /F z0 P/P 0 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 F z0 α~ -0.2 β~ -0.1 for a dual truck tire at road velocities RR behavior: pressure effect is strong, Load effect weaker Xone/duals

© Michelin Tire Corporation 18 Center Reinforced Low H/W (Xone) Design Goals 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) 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

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

© Michelin Tire Corporation 20 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 21 Behind the evolutions Enabling material technologies VulcanizationSulfur linking of rubber polymer chains Carbon Black (“Early nanoparticle technology”) Further reinforcement of rubber – tuning of compound viscoelasticity, elasticity, abrasion resistance Synthetic rubbers, natural and synthetic blends More rubber properties tuning possibilities Rubber/brass bondingStructural bond needed to make a belted radial possible, brass plated steel + special rubber mix provides high quality bond SilicaUsed with or in place of carbon black-new adherence/wear/rolling resistance trade off Open steel cable constructions Permits 0 0 reinforcing in crown without cable rupture