Several tire changes for NASCAR's Bristol dirt races this week

There was no question changes were needed in the Cup Series, which has seen the introduction this season of the Next Generation car which features an 18-inch bead diameter tire (they were previously 15 inches).

But Goodyear has gone further, changing to a radial tire this year instead of bias ply, which was used last season in the first Cup Series dirt race since 1970.

Bias ply tires are generally more compliant than radials and better able to envelope the inconsistencies of the dirt surface.

Goodyear designed its 18-inch tire with the lower profile sidewall to behave similar to a bias ply tire, but with the size-matching capability of a radial.

“We had to develop a new package for the 18-inch dirt tire this season, so it gave us the opportunity to totally re-imagine this Cup tire set-up,” said Greg Stucker, Goodyear’s director of racing. “We felt the right move was for a radial tire, which provides a greater degree of size consistency.

“However, a radial tire incorporates a much stiffer tread surface, so we made adjustments to the tire construction to achieve a more compliant feel, similar to that of a bias ply, and able to handle the irregularities of a dirt surface.

“The 18-inch package also includes a new tread pattern which incorporates a lot of dirt tire technology we’ve developed over the years, and tread compounds adjusted to be more resistant to heat and wear.”

Goodyear ran a tire test in preparation for this year’s Cup race at Lancaster (S.C.) Motor Speedway with Truck series regular Stewart Friesen in a Next Gen car last December.

A confirmation test was held with Friesen at Bristol on April 6 once the track surface had been changed from concrete to dirt.

Goodyear 18-inch dirt tire overview

Photo by: Goodyear

Cup teams will received three sets of tires for practice, one set for qualifying and six sets for Sunday night’s feature race (five race sets plus the set transferred from qualifying).

For Saturday night’s Truck race, Goodyear also made some changes. Trucks have been running at least one dirt race a year since 2013 (barring the 2020 COVID-19-impacted season).

Truck Series teams will remain on bias ply tires but run two new Goodyear tire codes compared to what they ran last season on the Bristol dirt track. Both the left- and right-side tires feature tread compound changes to be more heat and wear resistant.