Tall, thin, FAST tires

Aug. 9, 2013

DeltaWing Project 56 LLC, which does business as DeltaWing Racing, says it is transforming the motorsports and automotive industries with radical innovation. A big part of that innovation is in the DeltaWing’s tires.

“For the dimensions of the tires, we wanted: 4.0/23/R15 for the front and 12.0/24.5/R15 for the rear,” says Simon Marshall, DeltaWing Racing lead engineer. “We determined those sizes through simulation using a couple of vehicle dynamics simulation software programs where we could test-drive everything about the car and we knew it was going to turn and handle well before we ever designed or built the car.”

The rear of the DeltaWing car was designed to do all the work. Marshall says that is where most of the aerodynamic downforce and weight is located. The rear tires have 15-inch diameter rims, which is typical of something like an IndyCar rim, in order to accommodate a larger size brake disc.

“The front also has 15-inch rims for brake discs,” says Marshall. “Rim size is all about getting brake discs in. Clearly with race cars, it’s not like road cars, where the bigger the rim, the better for some people. It carries a lot of inertia with it. Big rims aren’t necessarily good for performance. You get the rim big enough to fit your brake package.”

The DeltaWing’s testing took place in front of the world, at the 24 Hours of Le Mans, June 16-17, 2012, in Le Mans, France. The first set of tires taken off the car during an early pit stop showed little wear.

“The fuel economy concept of the vehicle allowed us to use very light, slim, small tires at the front,” says Marshall. “At the Le Mans race in 2012, we were getting just under 200 mph, and the lateral forces were 3G-plus in the turns and the tires were just bomb-proof.”

Marshall says because the front tires are small, there isn’t much demand placed on the front brakes: The front tires can’t support a lot of demand laterally and longitudinally.

Bridgestone, Michelin, Bridgestone

When the DeltaWing was first proposed as an IndyCar in 2008, it was going to be fitted with Bridgestone tires.

“They actually committed back then to making molds for the tires because they could make some show tires to present,” says Marshall. “It turned out they didn’t pursue the DeltaWing because of their other commitments in IndyCar. That’s when we went with Michelin. But now we’re back with Bridgestone and it was quite handy because they already had molds made.”

Marshall says both Michelin and Bridgestone had to put a lot of work into the construction, geometry and compounds involved in these tires because they were doing a job not seen before. He says both companies overestimated how stiff the construction needed to be on the front tires.

“There’s always promise of more development beyond where we are now. We can get a much more compliant front tire to give us more front grip.”

DeltaWing Racing says that going forward, it will be working with Bridgestone. The tire maker is now using the same molds with a different compound and construction to try to improve the current tires. Sizes will remain the same.

“Definitely there’s nothing worse for fuel economy than a heavy, wide tire,” says Marshall. “So the fuel-efficient cars like the original Honda Insight, the original hybrid Honda, they need to have skinny tires. If you take fuel economy seriously, you can’t do it with a regular tire.”    ■