If he's running TCS, it'll be a Tamiya diff.

Assembled some tires today using the new/old S Grips I got last week and some of the new super hard foams. They assembled much more easily than with regular hard foams and the current squishy tires. Overall, they don't feel a lot firmer than the usual foams, but I think they'll have a positive effect on tread squirm and the edge of the tire rolling under.

BTW: Glued the foams by applying a little Elmer's Spray Adhesive to the ends, letting them sit for 15 minutes, then sticking them together and inserting into the tire immediately. Works well, no hard spots.