Originally Posted by joe of loath
umm, its pretty much as you describe it. 10.5 is pro-stock, 21.5/17.5/13.5 is stock depending on where you are, and anything below 10.5 is mod.
Actually, it's even simpler than that, now, mod is anything less than a 13.5(at least going by ROAR guidelines), 13.5's are Super Stock(which is like Pro Stock or the old brushed 19 turn class), 17.5's are for Stock & 21.5's are more specialized, namely Vintage Trans Am racing(or certain classes of oval racing). And I think it works out pretty well....