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American LeMans
ALMS: Surface Science
In just the four early season races, the ALMS has run on a variety of distinct track surfaces.
John Dagys  |  Posted May 17, 2009   Tooele, UT
St. Petersburg proves to be a challenge for competitors, as an airport runway is used as the street circuit’s front straightaway. (LAT)

The American Le Mans Series has been widely recognized for its diverse grids, with a mix of cutting-edge prototypes and fire-breathing GT machinery. Where else could the likes of Acura, Mazda, Chevrolet, Ferrari, Porsche and BMW be seen battling on the track, while yet developing technology for future road-going vehicles?

While the cars are very much the stars, an often overlooked aspect of the Series is its diversity of tracks. In just the four early season races, the ALMS has visited Sebring, the historic ex-World War II airfield; St. Petersburg and Long Beach, two similar, but very different street courses; and this weekend’s event at the wide-open and fast-flowing Miller Motorsports Park.

All four venues offer unique challenges in car setup, thanks in part to distinct variations in track surfaces. Setting up a car on a bumpy track made from a combination of asphalt and concrete is vastly different to a predominantly asphalt street course or even a natural terrain track like the one found at Miller.

Developing the optimal setup for each particular surface is an art and a science, not only for the ALMS team’s engineers, but also for its technical partners. With tires being the car’s only contact to the racing surface, understanding the intricate relationship between a tire and the track surface it rides on is as the heart of research and development.

That’s why Series partners like Michelin take a hands-on approach, at the track and in the laboratory. Michelin uses a variety of tools in tire development, such as finite-element analysis, which can model a tire’s stresses and deflections. Empirical models constitute another important component of Michelin’s R&D, as they can offer a simple prediction of a tire’s behavior, based on observed conditions.

The most valuable resource, though, is clocking miles on the track.

“By testing at different tracks on different days, in different weather conditions, and with different chassis, Michelin can try to identify which evolutions offer improvement in most or all conditions,” explains Karl Koenigstein, Michelin’s ALMS technical team leader. “All types of pavement have different challenges: Some are fast wearing, some have low grip and some cause a drop-off in lap times.”

Extreme bumps at Sebring not only takes a toll on the tires, but also the car’s suspension components. (LAT)
Take Sebring for instance: The combination asphalt and concrete surface, coupled with extreme bumps in Turns 1 and 17, makes it a challenge in finding the optimal setup. Add in the surface temperatures, which could vary up to 30 degrees depending on concrete or asphalt, and Sebring turns into an engineering nightmare.

“The bumpiest parts are the cold concrete slabs as they're like rafts that move on shifting sand, and can change year to year,” says Dyson Racing chief race engineer Peter Weston. “You have to run higher and softer at Sebring than at other tracks, not just for the grip over the bumps, but for the comfort of the driver and the reliability of the car, with it being a 12 hour race.”

Very little of the car’s data generated at Sebring can be transferred over to other tracks in terms of car setup and handling, and the same could be said for tires. Through a decade of sportscar experience, Michelin has learned that a tire that’s perfect for Sebring won’t necessarily work well at other tracks. As different track surfaces demand different tires, Michelin tests multiple compounds at multiple tracks to determine which ones work best.

Street courses create many challenges, but none more than the lack of pre-event testing. With these temporary circuits being located on actual city streets, the rush of daily traffic and activity prevents teams and tire companies from conducting ‘real life’ tests prior to a race weekend.

So how does Michelin develop a tire for a street course? It’s simple. They mainly rely on the previous year’s data, and if it’s a new venue, Michelin works with its technical partners to provide circuit estimates. Through state-of-the-art devices such as vehicle dynamics simulators, teams and manufacturers are able to gain valuable data estimates such as g-force loads and cornering speeds.

Michelin also develops casts of track surfaces to help gauge the roughness of a particular circuit, as well as using smaller sections of longer, permanent road courses to simulate the short and twisty sections of a street circuit.

Compromises often have to be made when setting up a car for street circuits with tall kerbing. (Marshall Pruett)
Casts are created by pouring a silicone mixture into a small square frame situated on the track surface. Once it’s cured, engineers have a negative of the track surface, giving them valuable data to help develop a race tire. Michelin also uses casting for its passenger-line of tires.

“If we have the opportunity to test before the race, that helps quite a lot but it’s not uncommon to race without that opportunity,” Koenigstein says. “Most new tracks that are built happen to fall within the range of extremes that we have in North America, so it’s unusual to have a new track offer up something beyond what we’ve seen before.”

In addition to the lack of track time on a street course, engineers face the challenges of developing their setups to accommodate the tall kerbing and occasional patches of concrete. It’s a give-and-take process, as it’s impossible to setup a car to ride all of the kerbs without sacrificing aerodynamic performance.

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