Originally Posted by Glenn
Maybe, maybe not, every manufacturer seems to come up with different dimensions on tires of the same numerical size. What I see when I read that a tire is 315mm size, is a 12.5" section width, which IMHO is too wide for a 10.5" wheel. I would think a 11.5" wheel would be a better match. Then again, everyone has different ideas about what is and is not a good fit, so YMMV.
Well, there's "ideal" and then there's "workable". Generally, wider rims are more "ideal". See Carroll Smith or Wm. Mathis books.
Kumho 710's seem to run wide. 275's look better (i.e., straighter sidewall) on my 10 1/2" rims than on 9" ones.
Even so, I'm going to try 315's this time around. If I like them, I may finally spring for some even wider CCW's. Those 315's are some expensive tires, so I will be sure and check my alternator output first.
Also, I think you can get away with more in auto-cross than for track use. Or at least due to class rim width restrictions, you see a lot of very wide tires on not so wide rims on very quick machines. E.g., 275's on 8" rims on F Stock Mustangs and also on D(?) Stock Rx8's. So, "workable" seems to trump "ideal", especially if there's no choice/budget, etc.