Tire fitment to kit wheels

[The Fisherman]

I'm stuck. Picked up at set of AMT Goodyear tires to finish off Twisted Fish and ran into a problem I haven't been able to find an answer about. The AMT tires (F60-15 and L70-15) are both narrower than the Revell wheels and backer. I've shaved thickness from both pieces and dished the backer as much as I can to set the wheel into it and the pieces are still too wide to fit either tire. 

Is there a trick to using these tires, or do I simply make a new backer to fit? I have no problem doing that, I just feel as if I'm missing something with the usage of these popular tires.

[Ace-Garageguy]

It's very common to have to modify the width of wheels, or swap or make new backs, to fit specific tires. Sometimes it's even necessary to shave the inside diameter of the tire as well.

You're probably not missing anything. Trust your judgement and do what's necessary to get the look you want. 

[Roadrunner]

I just went through the exact same thing on a'69 GTX I'm building. I discovered the problem too late, so used lead wire to shim the inside wheel, forcing the tire outward. It's a jimmy rigged fix, but I'll know better next time.

[Force]

If the tire is hollow you can fill the inside with balls of paper towel or something similar to hold the tire sides out against the rim edges.