Jon, I measured the tread width on my 315's and my R12's and they are the same width or the 315's could be 1/8-1/4 inch wider. Both are right at 9 inch in there width. I was a little supprised by this, but the 315's are much wider when you get to the belly of the tire, so I would not put 315's on a 8.25 wheel. It will be very close to touching without the bouncing that bus's do. He said when they kiss the heat will start to build.
