In a first for the NASCAR Cup series, cars competing in the upcoming Bristol dirt race on March 28 will be running on bias ply, rather than radial tires.
According to series supplier Goodyear, there are three key differences between the dirt tires and those usually run on asphalt. First, the bias-ply tires are more compliant and able to envelop the irregularities of the dirt surface. Second, the tires have a block-style tread pattern rather than a slick tread. The leading edge of the blocks bites into the dirt and the grooves in the tread help evacuate the dirt. Third, although the size of this right-side tire is similar to what teams are accustomed to running, this left-side tire is significantly shorter to build in more stagger between the left- and right-side tires. The tire is based on a dirt-modified model in Goodyear Racing’s tire line, though it has been widened out to 11in (from 10in on the dirt-modified tire) to give the NASCAR cars and trucks more grip. As on most NASCAR ovals one mile or less in length, teams will not run innerliners in their tires on the Bristol dirt track.
“Our tire setup for Bristol this weekend has several obvious differences between what these teams are used to running throughout the NASCAR season,” said Greg Stucker, Goodyear’s director of racing. “Goodyear started its transition away from bias-ply tires in NASCAR in 1989, so none of these drivers have driven a Cup car on anything but a radial tire. Bias ply tires are much more compliant than radials because they don’t have a belt package under the tread, making it more able to conform to an uneven dirt surface. The other obvious difference between these tires and the ones teams run on Bristol’s concrete surface is the presence of a tread pattern. All of our tires have a tread, but the concrete and asphalt tires do not have a tread pattern. These dirt tires have a block-shaped pattern, both to bite into the dirt and to evacuate it so the cars have grip.”
NASCAR Cup Bristol dirt race tire specs
Tire: Goodyear Eagle Dirt Bias Ply
Cup: Three sets for practice, one set for qualifying race and five sets for the race (four race sets plus one set transferred from qualifying)
Truck: One set for qualifying race and three sets for the race
Left side – D-3044
Right side – D-3046
Left side – 2,179mm (85.79in)
Right side – 2,248mm (88.50in)
Minimum recommended inflation:
Left front – 18psi; left rear – 18psi
Right front – 22psi; right rear — 22psi