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Technology

Observer

By James Worrell and Michael W RobbinsAugust 2, 2004 5:00 AM

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HIGH-PERFORMANCE TIRES

They still look the way they’ve always looked—round and black. But they’re so much better now that they can be driven continuously at speeds up to 186 miles per hour and can handle as much as 50 percent more lateral force before slip-sliding away.

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rubber

Ultrahigh-performance tires like Bridgestone’s new Potenza S-03 Pole Position aren’t made of sap from the rubber tree (Hevea brasiliensis) anymore. They’re completely synthetic, based on petroleum polymers. The S-03 is built with about 30 chemicals, including carbon and sulfur. Fifteen different rubberlike compounds are precisely positioned throughout the tire, each having a different function. One compound in the sidewall, for instance, protects tires from ozone and sunlight. W-rated (168 mph) and Y-rated (186 mph) tires designed for summer driving are compounded to function best at a temperature of about 150 degrees Fahrenheit.

plies These layers of cord or wire are embedded in rubberlike compounds. The basic body plies encircle the tire with two layers of rayon. Next, two steel-wire plies angled at about 70 to 75 degrees maintain the shape and provide the toughness necessary to handle collisions with curbs.

Outer Tread The outer-tread layer is a compound so soft that it actually molds itself to the contours and irregularities of pavement, thus providing the requisite grip for hard acceleration, braking, and cornering.

cap plies Designed to counter the extreme centrifugal forces of a tire moving at 1,000 rpm, the cap plies are made of two layers of nylon. These layers also keep the belts flat and the tread surface in contact with the pavement.

bead All tires attach to wheels by locking in under a flange on the wheel. High performance calls for extra strength in the bead area to deal with increased centrifugal and lateral forces. A tight bundle of up to 16 steel wires embedded in the hardest rubber compound in the tire provides that strength and delivers a precise “feel,” the benchmark of a performance tire.

tread A racing slick with no tread pattern puts the most rubber on the road and thus delivers the best performance. But on wet pavement, a slick tire hydroplanes, or rides up onto a film of water, and loses contact with the pavement. Tread patterns are always a compromise between maximizing contact and minimizing the chance of hydroplaning. Specially shaped tread elements, randomly placed, reduce road noise.

second-tread layer This layer is a compound that acts as a backup to the not-as-soft layer on the surface. As the tire ages and hardens and the tread wears, more of the grippier second layer is exposed, keeping performance levels high.

grooves On the S-03, curved indentations squeegee water away from the tread. Groove walls gain greater efficiency from microscopic scoring, a design based on NASA research into why sharks create so little turbulence (sharkskin has numerous microgrooves).

weight At least two tire manufacturers, Goodyear and Michelin, are now experimenting with different combinations of ply materials, compound additives, and manufacturing techniques to build even lighter ultrahigh-performance tires.

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