( I did not check that there was a page 2 with the answer 
here is my post anyway)
if you are really into sumo this book is great!
His secret is simple. He coat is wheels is silicone, he use RTV ( Room Temperature Vulcanising ) use around motor gasket.
You use a credit card to apply a very thin layer of silicon to the wheel.
I had some very used 3 kg sumo wheels from my sumo rhino and there were so teared appart. I was going to the national canadian robots games and I had to fix them. I put the wheel in the lathe, I took this cheap credit card and mounted to the tool holder, aligned everything perfect.
I then added silicon on the wheel. I hand turn the lathe slowly while the credit card was barelly touching the wheel. It was really perfect and smooth!
I let that cure for 24h and got some nice wheel!
I then won #1 place 
www.youtube.com/jeromedemers
I even took pictures of the procedure, but I do not have them with me.
Pete also explain that secret in a servo magasine in the “ask mr roboto” section. I have no clue of the issue.
Good luck
Jerome
