I've got a question about rear tires. I've broken out my stash of offroad cars and they're ready for the season, but some of my rear tires are acting funny.

I don't run a lot of camber on the rear, -1 to -2 typically, but some of my rear tire sets are coming off of the track coned in overall profile after a 6-10 minute run. As in, the outer diameter is smaller than the inner diameter, like you see with onroad foam tires. Smashing the insert around some brings the tire carcas back to it's expected profile.

Is this an indication that my open cell foam inserts are needing to be replaced?