New tires keep rolling longer: advances in compounds end performance compromises.

Some say the entire U.S. tire industry was the beneficiary of a divisive mid-1980's takeover bid for Goodyear Tire & Rubber Co. In repelling that takeover play, Goodyear was forced to close three plants and sell off a couple more. The resulting global restructuring (and expensive buyback of its own stock) drained the corporate war chest and cost thousands of jobs.

In the end, though, Goodyear emerged leaner, meaner - pre-conditioned for the in-your-face attitude that's de rigeuer for suppliers doing 90's-style business in the auto industry.

Through the tire industry's recent travails - Bridgestone/ Firestone Inc. has yet to resolve a rather nasty strike by the United Rubber Workers union that began nearly a year ago - one business strategy remains stable: Every company's headlong rush to market new products made possible by profuse advances in tire technology.

This heady new technology is driven by the ever-changing demands of every tiremaker's two primary "customers:" retail consumers (replacement tires) and automakers (original equipment tires).

Michelin's research says the most desired attribute consumers look for in an H-rated replacement tire has shifted from dry handling to improved wet traction.

This newfound consumer preference for wet-weather performance is borne out by the almost phenomenal sales performance of Goodyear's Aquatred line. Based on The World Tire Industry, a research report by The Economist Intelligence Unit in Britain, Goodyear sold more than 2.5 million Aquatreds in the tire's first two years on the market. Some skeptics claim it was Goodyear's heavy spending to market the Aquatred that actually "created" in consumers' minds the need for enhanced wet performance.

Either way, other tiremakers - whether or not they'll admit it - find themselves chasing the Aquatred's direct hit on consumers' wallets.

Michelin & Cie, for instance, explains at this year's gathering of its highly regarded Tire Technology Workshop that the company's new Energy MXV4 tires are the Aquatred's equal or better - depending on how it's compared - in wet performance, while offering quantifiable advantages in other aspects of tire performance, most notably rolling resistance.

What's so important about rolling resistance? Reducing it has become the top priority for automakers (see chart) - consequently, they heavily stress its importance to tiremakers developing tires for OEM business.

It's all due to government mandated Corporate Average Fuel Economy (CAFE). Michelin says its studies show that overcoming rolling resistance - the force required to keep a vehicle's tires moving at a uniform speed - is responsible for a hefty 25% to 30% of the total energy needed to move a vehicle.

Mike Wischhusen, manager of product engineering at Michelin, says a 5% reduction in tire rolling resistance translates into about a 1% fuel economy boost. That's a big gain, but it doesn't come easy. "Rolling resistance is the most difficult (tire) performance aspect to optimize without hurting other performance parameters," says Mr. Wischhusen.

That's the rub.Traditionally, to get low rolling resistance, tires had to be composed of "hard" compounds and inflated to high pressures. Hard compounds meant lousy wet and dry "grip," and high pressures usually translate to jarring ride quality. One development engineer for General Motors Corp.'s Impact electric car compares early-generation low-rolling resistance tires to "driving on banana peels."

Welcome, though, the breakthrough: silica. Michelin's rubber compounds brewed with silica have reduced low-frequency hysteresis, which means low energy absorption and low rolling resistance. But the silica compounds enable the tiremaker to retain advantageous high-frequency hysteresis - necessary for high levels of wet- and dry-surface grip.

"Silica lets us overcome the link between traction and rolling resistance," crows Michelin's Mr. Wischhusen.

Michelin uses silica compounds in the new Energy MXV4 and will market it in other lines under the umbrella of Radial XSE Technology. The company says some Radial XSE applications can reduce rolling resistance up to 35%, giving an immediate 5% fuel economy improvement. Further, it says that if all passenger cars in the U.S. were fitted with Radial XSE tires, 2.4 billion gallons of fuel would be saved annually and 23.3 million tons of emissions would be eliminated.

The Michelin folks aren't alone in chasing the wet-dry handling/low rolling resistance bogey. Bridgestone/Firestone's new line of performance radials, the Potenza series, in addition to employing that wonderful silica, uses "long-chain" carbon black structures.

Carbon black is the most common reinforcing material in tire compounds, and Bridgestone says that by elongating the "bonds" between carbon black particles, any given tire compound can deliver reduced rolling resistance, better wear and, when combined with silica, demonstrably improved wet traction.

In its new Potenzas, Bridgestone has combined these compound advances with computerized finite element modeling for tire design and a subtle new bead design that allows a better, more consistent mount of the tire on the rim, which in turn means improved straight-line stability and ride quality.

The S-02s that the company bravely permitted recently to be hammered around the Road Atlanta circuit on Porsche 911s are the most impressive high-end street tires this writer has driven; the medium-performance Potenzas are equally qualified.

Tiremakers are working more diligently than ever to meet today's incredibly divertgent market expectations. Their developments may be some of the most significant, yet largely discounted, contributions to the overall level of safety and economy current vehicles deliver, but tire engineers appear simply to be glad to conquer some longstanding compromises in tire technology.

"Rubber chemistry has advanced to the point where we don't have to give up so much anymore," Michelin's Mr. Wischhusen affirms.