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?