Insider Knowledge: A look at the tires used on the IndyCar circuit

The Indianapolis 500 (AP Photo/Tom Strattman, File)

There’s a scene in the film Rush where actor Daniel Bruhl, as Formula One driver Niki Lauda, tells his future wife there’s a problem with her car. He knows, he says, because he has “an educated ass.” She doesn’t buy it but, sure enough, the car breaks down.

Dale Harrigle, chief engineer and manager of race tire development for Firestone, relies on drivers for constant feedback during the IndyCar season, but most testing takes place via computer simulation. Firestone is the only tire supplier for IndyCar; it manufactures 28,000 Firestone Firehawk tires in its workshop in Akron, Ohio. Each tire is handmade, and the right front differs from the left front, while the right back differs from the left back. Harrigle says there are 68 different specifications for tires for the 2016 race season, and Firestone will always bring a few test tires to each event for the week’s practice. Each Indy team will go through approximately 200 sets of tires: 52 for road courses (primary and alternate compound), 60 sets for street courses, 36 sets at the Indianapolis 500, 43 oval sets and six sets of rain tires.

The softer alternate tires, which allow drivers to take corners more quickly but wear down faster, are identifiable by the red stripe around their rims. Rain tires have a grooved pattern to prevent hydroplaning. And do you want to know why pit crews are so fast? Indy cars have one nut, specially built by Dallara, the Italian company that builds the basic car used by all teams. These are not your regular hexagon nuts: They have vanes inside them, and the sockets have teeth that are shoved into the vanes. The pneumatic impact wrench to remove it costs $4,500, and each socket runs about $1,500.

Let’s reinvent the wheel! The earliest tires were strips of leather placed on wooden wheels. The first patented pneumatic tire was designed in Belfast in 1888 by a Scottish-born veterinarian named John Boyd Dunlop, who built it for his 10-year-old son’s tricycle. The patent was eventually made invalid—another Scot, Robert William Thomson, actually lodged a patent 43 years earlier and teamed with Charles Goodyear on the development of vulcanized rubber—although the tricycle tire provided the basis for the Dunlop Tire Company.

The 2,300-lb. Marmon Wasp, winner of the first Indy 500 race in 1911, had tires 34 inches in diameter and 4.5 inches in width, of which only 2.5 inches covered the track. Nowadays, each tire covers 10 inches of track. The Wasp’s tires were constructed from fabric plies that featured two grooves in the tread. Current Indy tires are a hybrid of radial and bias-ply tires. Tire sizes increased gradually until 1965—when Jim Clark won the Indy 500 with 9.2-inch Firestones during the height of that company’s battle with Goodyear—and the size of tires has remained in the 10-inch range since then. (Eddie Cheever’s 1998 title was won with 9.75-inch fronts, when Goodyear attempted to reduce aerodynamic resistance by making tires that were narrower and shorter than Firestone’s.) A simple question worth asking: How do the people who make tires describe their purpose? “They allow drivers enough grip to utilize the performance of the car,” says Harrigle. “Indy cars weigh 1,800 lb. with fuel and can go from 0 to 60 mph in just over four seconds. At certain tracks, they hit 230 mph. So we’re talking about security and confidence for the driver.” Consider that the rubber soul of the tire.

To begin with, racing tires aren’t filled with air. It’s nitrogen. Why? Mr. Taylor, your Grade 10 science teacher, could tell you: Air, which is 78 percent nitrogen, contains moisture. Pure nitrogen, by contrast, won’t vaporize and expand when the tire heats up. And as Allen McDonald, chief engineer for Canadian driver James Hinchcliffe, explains, “You wouldn’t be pleased with the longevity of these tires. There’s a huge amount of grip on them, and they wear down quickly. Plus, they’re way more temperature-sensitive than normal car tires.” Harrigle says most of the technological carry-over from the racing to the commercial market relates to the development of polymers that eventually find their way into
consumer tires. Perhaps racing tires’ most significant impact on the commercial market comes, he says, from understanding how various compounds react at extreme temperatures. Good to know if you’re driving across the desert—educated ass or not.

This story originally appeared in Sportsnet magazine. Subscribe here.