In archaeological terms, the Indianapolis Motor Speedway Museum is that rarest of dig sites.
Tracing the history and evolution of the automobile, at least in its competitive form, can be achieved by taking a remarkable stroll through the IMS facility. Starting with the Marmon Wasp, winner of the inaugural Indy 500 in 1911, all the way through to Dan Wheldon's Dallara-Honda that won the great race in 2011, plotting the arc of development with racing tires makes for a fascinating look at how that piece of technology has developed over 100 years.
Armed with a measuring tape, notepad and behind-the-ropes access prior to the museum's opening, the Marmon Wasp was used as our anchor point to build a chart of front tire width expansion over a century of innovation.
With a diameter of 34 inches and section width of 4.5 inches, Firestone's 1911 Indy 500 winning rubber was constructed from fabric plies using a "gum-dipping" method that features two grooves in the tread. Despite the 4.5-inch width, the tires only put 2.5 inches of tread—the actual patch—to the ground on each corner. That's 10 inches of total tread for a 2300-pound vehicle, and those tires were production Firestones, rather than specials produced for racing.
Move from the teens to the late 1920s and tire technology made strides in construction materials and methods—smaller 32-inch diameter "Balloon" tires came to the fore a bias plies replaced fabric—but the patch increased just half an inch to 3 inches on the 1928 Indy 500-winning Miller.
By 1941, 30 years after the first Indy 500, front tires had yet to double in width. Firestone's "Deluxe Champion" tires, employed from 1939-1963, were shorter at 28.5 inches in diameter and continued to use bias ply construction, but the proverbial light bulb had yet to happen as the winning '41 Wetteroth chassis was driven to victory on thread just four inches across.
It took 44 years for front tires to grow by an appreciable amount with Jim Clark's race-winning 1965 Lotus-Ford sporting 9.2-inch Firestones, and, oddly enough, despite furious tire wars between Firestone and Goodyear took place during Indy's most adventurous decade of design, what came out of that era—at least in terms of tire widths—has seemingly remained frozen in time.
Mario Andretti's 1969 Indy winner rode on 10.5-inch treaded fronts, and by 1972, proper racing slicks were adopted, doing away with the production-based tread concept, but the 10-inch range would continue to reign.
Al Unser Sr.'s 1978 Indy winner dropped down to Goodyears that were nine inches, but something in the 9.75-10.5-inch variety has held sway over the Speedway ever since.
Jacques Villeneuve's 1995 Indy winner had Goodyears at 10.5 inches up front while Eddie Cheever's 1998 500 winner used Goodyear's narrower 9.75-inch fronts—a successful attempt by the Akron-based brand to reduce aerodynamic resistance by building front tires for the 1998 race that were narrower and shorter than what Firestone created.
And in a nice bit of symmetry, Wheldon's centennial Indy 500-winning Firestones were 10 inches wide at the front—the sum of all four tires on the 1911 winner.
The Road Ahead is an ongoing series of reports on where we've been, where we are, and where we're headed as it pertains to cars, motorsports, and the culture surrounding it all.