Pardon my laziness, but I thought that an experienced autocrosser may have already dealt with this issue. I have an E30 M3 with a completely stock suspension. I'm trying to determine if I bump the car out of its stock "C" class if I put 15" Kosei wheels with 225 tires on it. The relevant rule says that I can use "any wheel of stock diameter that does not require wheel spacers or body modifications, provided tire contact patch does not extend beyond fender opening when viewed from the top, perpendicular to the ground." So the wheels should be good, being 15" and not requiring spacers or fender bashing. But what about the tires? I'm not sure how one determines if the tire contact patch itself extends beyond the fender opening. It's not really something you can put a level bubble on. 205s on the stock wheels are clearly within the fender wells, but 225s would probably push the tire sidewalls to the fenders, particularly if you are supposed to consider the entire fender and not just the outermost portion of the fender flare. So have any E30 M3 drivers dealt with this issue? And if so, with what outcome?
Yep, specifically the rules posted for the '14 O'Fest. But are those different than the rules that apply to regional CCA autocross events?
If your local chapter runs autocrosses, they probably would have rules, class designations, rules, etc. on the chapter website. If not, contacting any local chapter poobahs should get you a lead on their auto-x rules... or were you asking because you're coming to O'Fest?
I was asking because I'm coming to O'Fest. It's interesting that different chapters use different rules. My local chapter does not do autocross, but the neighboring Colorado chapter has an extensive autocross program and uses a points system for modifying -- something akin to the NASA autocross rules. I had assumed that they were unusual in using their own rules, but now I gather that the O'Fest rules aren't widely used in regional events.
Hopefully someone with an E30 M3 who brings & auto-x's it @ O'Fest will pipe in - my guess would be that if you're close (like a few mm, or less than 1/2", & not visibly noticeable), it's probably unlikely your car will be so closely scrutinized that organizers will bump you up a class. O'Fest classing verification seems a bit on the honest-system, I think relying to a degree on people's integrity to comply with the spirit of the rules. If you think it looks close, just be ready to accept that organizers might bump you up. There is variation from maker-to-maker in widths, so tire choice might make a difference, possibly, though I'm not sure if it would be enough to be an issue.
Thanks for the response! Or I could stop being lazy, bolt the wheels on the car, and take a few measurements.
I don't read anything in the stage one dictating tire size. In my opinion these rules have huge gray areas open to very liberal interpretation. Your reference to wheel size/fender clearance rule is not the same as tire size and therefore should not have any consideration on what tires you choose to use. Furthermore, they specifically state in stage 2 "Tire contact patch may extend beyond body-work." Also, it's interesting to note that factory tire size on the euro E30 M3 is 225/45/16. In conclusion... you're fine.
