I would venture to say 11.50 would be as wide as you want to go. I have 12.50's on an 8" wide rim. Now with that said, when you purchase your tires I would suggest you get the size you want and not the size that is limited to your rim. Tires are very expensive when you get to the 35" and up range, you don't want to regret your purchase down the road. As of right now, if I had purchased 15" rims I could be rolling on 37's for the same price I paid for my 35" MTR's on a 16" rim. Just something to think about.