Skyway and similar companies provide a selection of wheels with varied durometer rubber treads. Our tires have, on recent robots, been in the mid-high double digits durometer-wise and have functioned well (keep in mind that we use tank drive. results would be different if you use skid-steer). Another resource would be AndyMark.biz and their omni-wheels. However, shipping was as of 5:00pm and the fix-it window has closed, so I'm not sure what options are left open to you. Hope this helped.

Michael Greenley

P.S. Spellchecker was picking up durometer, but didn't have any suggestions, so I apologize in advance if that's a mis-spelling.