Goodyear comes with tires that have been tested earlier by random choice race teams to see what compound is best for that surface in the codition it is that season. As long as it is a Goodyear issued tire Nascar would not care what they run ie. they could not run a Firestone or Hoosier tire. You are correct the teams have to turn any left over tires back in to Goodyear every since a chemical company said they were furnishing the 24 team with a nondetectable chemical to soak their tires in and making them more sticky. Lots of things have changed since I was a member of a team and with my memory problem a point I am not real sure about but I think that if you want x amount of tires for a race you don't get credit for any you don't use. Use to some of the start and park teams actualy bought used tires from the better funded teams as well as clutch disc, alternaters and any parts that the A teams changed after one use.