[junefish]

I can't find anything against them in the rules either, but I wouldn't advice the use of pneumatic wheels simply because of the weight restrictions. Weight is always an obstacle, and pneumatic wheels weigh a lot. I did a quick Google search for 20" bicycle wheels, and found a "incredibly lightweight" bike that weighs 19.6 kilograms (about 44 lbs). True, that weight included the frame, but since you were planning on having 4 wheels (not 2) I would guess that the wheels alone would weigh at least 30 pounds--never mind the rest of your drive train! Also, I would be concerned about the strength of the tires--from match to match your robot goes under a lot of stress, and you don't want to get a flat tire.

Hope this answers your question.