Which is harder to design-a racing tire or a passenger tire?
According to top officials at tire companies that manufacture both, that's rather like asking which is harder to grow-an apple or an orange.
``They're so very different that they're hard to compare,'' said Julian Baldwin, director of marketing and motorsports for Cooper Tire Europe Ltd. ``A race tire has a life of 20 to 30 minutes, an hour at most. A street tire, however, must last several years.''
In the broad sense, a road tire is harder to design than a racing tire because there are so many more performance characteristics to consider, noted Frank Secondari, senior product engineer with Kumho Tire U.S.A. Inc.
``But in racing tires, you must have things so optimized, and you're looking at such a small differential to give you that extra edge, that the design targets you're trying to hit are extremely small,'' he said.
Al Speyer, executive director of motorsports for Bridgestone/Firestone, enumerated the performance characteristics tire makers and race car drivers seek in racing tires: speed, traction, heat resistance, acceleration, braking. Those things aren't exactly unimportant in passenger tires, Mr. Speyer noted, but treadwear and wet traction are the qualities most street tire buyers seek. Wet traction isn't a factor in race tires, he added, except for race tires designed specifically for wet track conditions.
``Noise is also a major factor in street tires, whereas it's not an issue at all in racing cars,'' he said.
The different design imperatives present different challenges for tire engineers, noted Karl Koenigstein, technical team leader for motorsports at Michelin North America Inc.
``A passenger car tire can't afford to be terrible at anything,'' Mr. Koenigstein said. ``It has to be OK in dry conditions or in rain and usually in snow as well. It has to be OK for comfort and noise and at a reasonable price point. It has to be a variation on a theme, from a small tire for a compact car up to a high-performance tire. But both the high-performance tire and the small tire have to fulfill all those purposes.
``A purpose-built racing tire does only one thing well, and that's getting around a race track,'' he said. ``It doesn't matter if it's not comfortable, it doesn't matter if it's noisy or doesn't last long.''
The actual manufacture of racing tires also differs considerably from that of passenger tires, said Stu Grant, Goodyear general manager for global race tires.
``A lot of manual labor goes into both, but the manufacture of passenger tires, because of the volume, is much more automated than race tires,'' Mr. Grant said. ``In race tires, the manufacturing process is much more hands-on.''
All the executives agreed that the design process for a new racing tire is much briefer than for a passenger tire, though Mr. Secondari said he doesn't believe the processes were very different per se.
``In both processes, you generally start out with something that's existing, define your targets and goals, and go through your normal design cycles,'' he said. ``You develop a mold profile, develop the compounds, develop a tread pattern-though race tires, in many cases, have no tread pattern.''
Whereas a passenger tire will remain years in development, a race tire must be finished within months, or sometimes even weeks, the executives said.
Mr. Koenigstein noted that Michelin began designing a new tire for the Audi R10 racing car in June 2005, immediately after that year's LeMans race. That tire won the 12-hour race at Sebring the following March-nine months after the original conception. A new street tire, meanwhile, may take 36 months to develop at Michelin.
When asked how often racing and passenger tire design influence each other, some executives said it was overwhelmingly race tire technology that influenced street tires, though some said it was more of a two-way street.
``There used to be very little crossover between road and race tires,'' Cooper's Mr. Baldwin said. Most often it's race tire design that ends up eventually in passenger tires, he said, but some compounding technology that originated at Cooper in street tires has made its way into racing tires.
Mr. Baldwin also said that Cooper still manufactures Avon-brand racing tires for the United Kingdom and some European markets, while the Cooper brand is used for racing tires sold elsewhere.
Race tire technology played a major role in the development of BFS' UNI-T Ultimate Tire Technology program, according to Mr. Speyer. Technologies the tire maker developed through UNI-T include CO-CS, Computer-Optimized Component System; the O-Bead bead cable, which eliminates the overlapped bead joint for rounder tire assembly; and Long Link Carbon, a carbon black with long chains of particles that allow greater wear resistance than the shorter particle clusters in traditional carbon blacks.
Goodyear often must evaluate new compounds and materials in a matter of days or weeks for race tires, Mr. Grant said, and much of that design work ultimately ends up in the company's street tires. The company's Formula 1 activities provided the impetus for both the directional tread tire for the Corvette and the carbon fibers in Eagle HP tires, he said.
The ``race wrap'' design that promotes durability in the Eagle GT-HR tire began with Goodyear's NASCAR involvement, Mr. Grant said.
``We have a long history of track to street,'' he said. ``As the design of tires moves to computer modeling, the thing we transfer most in engineering modeling technology is the up-front design work in race tires to other technologies.''
A race last October at Loews Motor Speedway in Charlotte, N.C., for example, resulted in a new mold shape now being used on both the race and street sides, he said. And Goodyear is moving quickly toward commercial application of radio frequency identification of tires after using RFID in all its NASCAR tires this year.
Despite the extreme speed at which race tire designers must work, most of them find it a liberating experience, according to Mr. Koenigstein.
``When you design a race tire, you don't have to worry about comfort or price points,'' he said. ``You don't have to worry about its working in Minneapolis. A LeMans-type tire has to work for 24 hours, and that's it. That liberty of design leads you to concentrate your efforts on a fairly narrow area. That's why engineers like that challenge-it's engineering taken to a very narrow extreme.''