Listen to this article 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 ri …