Originally Posted by Granpa

If you're referring to the to the 60D series of tires, The Tamiya hard foam insert seems to be the best. Unfortunately. you should contact or rubber cement the ends together. Shimizu makes an insert that you don't have to do that with, but IMO is too soft. The insert that comes with the tire should be discarded.

Use the 456 or 454 in front, and the 454 or 452 in the rear. Te 450 for some reason just does not work.