The best wheels are treads!
The technocats, team 45 have sweet custom treads, make of metal cleats on a chain.
They were some good pictures a while back, suffice to say they don't have traction difficulties
. They can tell you more, though, and if you go to their site(at least when I went), you could see some movies of their robot in action. In the background, you can here the drive train. Sounds like a M134 chaingun on an apache winding up
Great job 45!