These DIY molded rubber wheels might be perfect for your next robot.
The mold rubber used was Smooth-On part # PMC-121/30 Dry.
The alternate wheel hub will hold the rubber more securely but may be more difficult to print on some printers. The aluminum hub to attach to the motor is not included, but this should work.
More robot related information at http://www.iheartrobotics.com
0) Print two sides, one base and a hub to make one wheel.
1) Sand and seal the sides and base with a clear spray enamel. Do not seal the hub, it should remain porous.
2) Assemble the sides and base with screws, and apply mold release. Do not spray mold release on the hub and do not attach it until after mold release has dried.
3) Mix mold rubber according to manufacturers specifications and pour into convenient funnels mounted on the side.
4) Tap gently to remove air bubbles and let cure.
5) Wait patiently.