My Dad the Radial tire engineer discovered that the tires did not cool like bias ply tires. The hook conveyor usually used to move hot tires from the curing mold machines would leave the radial tires out of round. It required the addition of a machine at the press called a post cure inflater that kept the tire round during cool down, and a ring around the tire blew cool air on the outside. Getting the slot car tires solid and round probably is one of the major failures we see in our scale tires. Good luck.