Other than the commonly-known variety (bull----) the other use of that term on automotive forums refers to "backspacing" -- in his case, 3 & 5/16ths. Backspacing and offset usually go hand-in-hand, although there are some variances. In any case, 3 & 5/16ths BS on an 8-inch rim would equate to an offset of -11/16ths, or in the more commonly-used metric, -17.5mm offset, or somewhere right around there. That's a pretty high negative offset, which would only serve to hit the fenders more than a neutral offset... So if you're planning on 0-offset rims, I'd bet you'd get away with the same tires without any issues at all... As for the 12.5's, well... Lemmie think about that a minute. Sweater's tires are set outboard an additional 17.5mm from where yours would be... In other words, his rims will emulate a tire that is 35mm wider than his tires really are, at least on the outboard side anyway. Frame rub is a different story, but as far as the fenders are concerned, his tires appear to be 35mm wider (approx 1.5 inches) than they really are. So the question is, Sweater, ya think you'd be able to fit another 1/4-inch of tire width on there without rubbing? Check it at steering lock where the tire comes closest to the fender, and speculate whether or not another 1/4-inch would be a deal-breaker or not...

-Chris

-Chris