To be honest, that is they way they should be, (off the car).
Ever notice, how the tires on a vehicle have a slight bulge at the bottom where it's in contact with the ground? And that some aircraft kits have an option of "weighted" tires?
On occasion I sand the bottom of the tires flat, but they don't get that bulge.
I don't care what my tires are made out of, just that they fit the build.