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Automotive Industry

The rubber meets the road

Automotive Design & Production, May, 2006 by Christopher A. Sawyer

Although it might seem that racing tires are in a class of their own: "It is much more difficult to design a street tire for the simple reason that the street tire has to perform under a much broader range of conditions," says Al Speyer, executive director Motorsports, Bridgestone/Firestone North America. The underlying truth of that statement hasn't stopped sanctioning race bodies from considering tires that can run under all but the worst weather conditions. Though it makes superficial sense, according to Pierre Dupasquier, former head of Michelin's motorsports activities, it is quite illogical. "When it rains, a race car heads for the pits to change the tires," he says. "It's a luxury the road car driver does not have. You must give the racing car what it wants."

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What does a racing car want? That depends on the type of car, type of track, and the conditions under which the race is run. Take the single-seaters that run in the Indy Racing League (IRL) and Champ Car World Series. They race on street circuits, permanent road courses, short ovals, and superspeedways. "A street course has an average speed of about 100 mph, and uses our softest compound and construction," says Speyer. It is so soft, he claims, hot tires peel the paint stripes off the road. On a permanent road course, average speed rises to 140 mph, and jump again to more than 180 mph on short ovals. "Those tires have progressively harder sidewalls and compounds to resist the heat build-up." For superspeedway work, says Speyer, "Sustained speeds are over 220 mph, and the compounds are the stiffest and hardest we make."

No real surprises there, except that a typical race tire has a tread face as thick as two credit cards, and requires unique processing techniques. "Racing tires have very wide, thin components," says Speyer. "It's a bit like trying to process a sheet of wax paper through the factory." The techniques developed for racing tires--when applied to sturdier materials--result in less distortion, and higher quality and consistency. Technologies like long-link carbon and smoother bead design have made the move from racing to road, with the former giving greater heat resistance, longer tire life, and retaining wet weather traction as the tire wears. The latter, a seamless rounded bead, reduces vibration.

What doesn't make the transfer--at least not in the same form--is the simulation technology used to create a new race tire. Dupasquier describes it this way: "We rely on sophisticated computer programs that allow us to look at the track right down to the granular level--to the shape of the pebbles that make up the surface. We measure the granularity, determine the abrasiveness, and look at how the corners flow together to determine the forces on the tires. This information is compared to our database of tracks, and we pull representative information in order to determine what will be needed." Speyer describes a similar process, but adds that--since racing is a travel-intensive pursuit--"it is populated by younger engineers who move back to the passenger vehicle side of the business as their career and family needs change." It is here--as well as through the regular meetings and design reviews--that information exchange takes place. Its value, says Dupasquier, "is that it changes the way you look at a problem, how you approach it, and what you do."--CAS

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Automotive Industry

The rubber meets the road

Automotive Design & Production, May, 2006 by Christopher A. Sawyer

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