I recently read an article on creating custom sumo wheels with different type of rubbers. I had to stare at the image for a good while to find the dimensions on their wheel and drew this up in Corel. Then I created a version for Bane! These are the dimensions (pretty similar) to the baltic sumo wheels.

Baltic wheels

Dimensions are very easy to change to adapt them to your motor and/or project. Here in the US a good compound to try is ReoFlex 20 from Smooth-On or go up >20 for more hardness.

NOTE: After casting my first tire I realized with the type of material I used to make my mold I needed to have a release agent, be sure to pick one up as well and if the surface is porous be sure to seal it first also.