3/30/15

In This Session

2015 Webinar 2 • Review: How a car turns a corner • Design variables • Inflation pressure Making Tires • Tire construction • Tread rubber Anybody can build a computer or a 747, • Cord materials tires are tough to manufacture. • Tread pattern • Manufacturing • Questions 3/31/2015

1 2 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Review: How a Car Turns a Corner The Tires Are Turning the Car

• Steering input creates a slip angle at the front tires resulting in a lateral force that starts to turn the car • The rear tires stop the car from rotating with a slip angle and lateral force • The combined lateral forces of the tires act at the CG accelerating the car toward the center of the arc of the The sidewall distoron you see is evidence of the lateral path forces generated by each re 3 4 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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History Tires Have Conflicting Design Requirements

• Wooden wheels in use for 5,000 years • Must be flexible but stiff enough to transmit cornering • R. W. Thompson patented the Aerial Tire in England, and braking forces 1846, vulcanized rubber not yet available • Curved shape has to conform to flat road surface • Balloon tire REinvented by John Dunlop in 1888 for • Tread - has to be soft for traction but wear well smooth and more efficient rolling of his son’s tricycle • Solution is a tread compound bonded to the outer • Bicycle and tire development progressed together diameter of a pressurized, hollow composite of stiff, • Solid rubber tires melted from hysteresis heating, 1928 strong fibers in a soft rubber matrix solid truck tire limited to 15 mph when fully loaded • Air pressurization is a great solution but people don’t maintain proper inflation pressure • Tire industry still looking for a non-pneumatic design • Michelin Tweel, closed-cell foam? No. TPMS!

5 6 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Flexibility Makes It Work Design Variables

• The conflict between a • A few design variables surface of double define the size of the curvature, and a flat plane contact patch at a given was an important factor in vertical load the decisions of designers • Rim diameter-brake to employ cords clearance embedded in rubber for • Outer diameter-fender the structure of a tire. clearance • Section height • Deflection of rubber between cords allows • Tread width conformation to a flat • Internal pressure surface determines CP area and prestresses cords

7 8 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Inflation Pressure Supports the Load Types of Construction Sidewall-Cord Differential Tension • Bias-ply, cord angle determines shape • Post-WWII roads in Europe allowed sustained high speeds, new type of tire needed • Breaker plies and belts flatten the tread area decreasing distortion for less heat generation, allowing better wear at sustained high speeds and a wider tread with less rubber thickness at shoulders • Radial-ply, belted construction requires different manufacturing method/equipment, US companies added belts to bias-ply tires

9 10 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Plies & Belts Generate Shape Construction Variables • Cord angle determines shape in bias-ply tire • Belt constrains tread diameter allowing wider tread with • Stiffer belt area generates thinner rubber, less distortion same lateral force at a smaller slip angle - less • Belts reduce distortion, heat generation induced drag • Non-belted race tires have a concave tread surface when uninflated - less stiff tread area than belted • Radial tires - higher forces with smaller CP deflection • Radial tires more efficient, but less forgiving at the limit

11 12 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Aspect Ratio History Basic Construction Components Lower aspect ratios generate big CP and quick response but also poor wet grip and • Body plies supply the impact vulnerability for tire and wheel basic structure • Beads anchor the plies, hold the tire on the wheel • Fillers and inserts add stiffness or flexibility to specific areas • Belts reinforce the tread area, restrict the OD • A butyl liner holds inflation gas

13 14 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Radial-Ply Construction Details Steel-Wire Belt Construction

• Radial sidewall plies • Rubber doesn’t stick • Belts with small angles to steel, so wire is brass plated • Stress-relief components • Stress relief devices everywhere at stiff/soft boundaries • Steel is heavy, but lower cost than Kevlar

15 16 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Radial with Wrapped Cap Fatigue Strength, Failure Modes

• Not true radial, • Metals: cyclic stress, cracks propagate from weak points, wire coat hanger example plies have an angle • Tires: bond failure in cord/adhesive/rubber system, void propagates, tread comes off • Tape-wound belt cap, probably • Any void in ply rubber fills with air at inflation pressure nylon • Firestone/Ford SUV problem similar to a plane crash, several simultaneous problems-mostly managerial • Nylon shrinks when hot, controls • In racing, failure can be delayed after damage, restarts on cold tires, low pressure tire diameter growth at speed • Tire failures due to manufacturing defects are extremely rare, modern tires very reliable and getting better

17 18 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Rubber Choices Stopping Distance on Wet Asphalt

• Rubber systems exhibit very different characteristics • Component parts in tires need specific properties Rubber Rebound Hardness Braking • For example, truck tires require reliability, long wear, low % Shore A ft. rolling resistance vs. low cost, wet traction for car tires BR 62 62 180 NR/BR 46 57 163 EPDM 32 63 160 SBR/BR 33 55 158 SBR 34 52 151 Butyl 9 40 130

19 20 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Cord Materials Filament, Thread, Yarn, Cord • J. B. Dunlop made a pneumatic tire with Irish flax in 1888, cotton replaced flax • A metal “spinneret” extrudes several polymer • Steel, Kevlar, and fiberglass are mainly belt materials, fibers and spins them into thread the rest generally are used in carcass plies • Threads are twisted into yarn, yarn twisted into cords • Number of elements, twisting left or right, loose or tight provides trade-offs of strength, flexibility, stiffness, fatigue resistance • Polyester variations dominate for sidewall plies

21 22 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Tread Design Trade-Offs Hydroplaning

• Treadless tires give best dry traction due to uninterrupted • Wedge of water in front of tire can’t support, Mario story later get out of the way, moves into the • Tread provides flow path for contact patch lifting the tire off the water, raises unit pressure road surface • Need lateral blocks at • No grip, no control shoulders for strength • Tread channels and road texture • Wear decreases water flow, allow water flow out of contact solutions include key-hole slots patch and high hysteresis rubber co- extruded in tread • Worse with more water, more • Multiple block lengths increase speed, wider tires, smoother road, frequency range of noise, same less tread level, less objectionable • Gator-Back pattern, Kenny • Ice is all about sipes, 2,500! Roberts 23 24 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Mario Andretti Discovered Slicks Delelopment Continues • New Michelin tire for the European • Tread pattern thought to market eliminates need for winter tire • “summer tire-level dry-weather be magic. 1960s performance with winter tire • Mario, “That’s air there, attributes” • Dry braking almost as good as a that’s not rubber.” summer tire • Went faster on • Wet braking and lateral grip in the ungrooved tires, slicks wet better than an all-season tire • Snow traction matches snow tires • No real engineering of • Wear as good as a summer tire tires, really, until • High-silica, low-hysteresis recently undertread compound for low rolling resistance • More flexible top tread layer for more grip year-round 25 26 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

Trade-offs and Compromises Tires Are Difficult to Design and Manufacture

• The pneumatic tire might be the most complicated and useful device made on earth • Tires allow a vehicle to turn a corner at speed • Without tires we’d all have to live within walking distance of a rail line, that would be a different world • Anybody can build a computer or a 747, tires are tough to manufacture • Tires are not a fully engineered product, but designed and developed by trial and error, in small steps, with great difficulty • A finished tire is a bonded unit made up of complex composites, not easy to inspect • Rubber changes with time, temperature, stress cycles, etc. • Tire manufacturing videos on youtube.com

27 28 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

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Teaser: What Does a Front ARB Do? The Racing & High-Performance Tire

Subtitled: Using the Tires to Tune for Grip & Balance Available on insideracingtechnology.com for $55 postage paid to U.S. addresses I sign all books bought directly from me Also available on sae.org and amazon.com to domestic and international addresses Web site: insideracingtechnology.com Email: [email protected]

29 30 Copyright Paul Haney, 2015 Copyright Paul Haney, 2015

SpeedSecrets.com SpeedSecretsWeekly.com HPDE-Instructor-Tips.com

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