I have a 2006 M3 with the competition package. I'm looking for some track only wheels and tires. Will 18's fit over the competition package brakes? I would also appreciate any opinions on tire size. Thanks.
Using the Tire Rack's wheel-selection options (tirerack.com) is an easy way to compare fitments. Tire Rack is conservative in their fitments, so if they have a wheel same specs as what you're considering, you should be good. Check the Tire Rack's tech section for details you need to know about wheel fitment. Besides the obvious width, diameter, & bolt pattern, there's also offset & center-bore. You can get a sense of the range of offsets that work for a given wheel width & diameter looking at the available offsets (shown on the left once the site puts up available wheels). If your track tires will be track-only, then I'd say go for the lowest profile (sidewall height) you can get for the desired tire width; that might be less than ideal if the plan is to drive 'em there, on the track, & back - always a risk of blowouts or rim damage from potholes, road bumps, etc. with tires with very little sidewall. Grip is fun, but, the price is short life - if you want something to make it more than maybe a weekend or two, avoid the 40-treadwear Hoosiers or similar & go for r-comps with 100 treadwear, or more. If it's to be a combo street/track tire, then perhaps look into ultra-summer performance tires, treadwear 140-200. If you've never done any driver's schools, hpde's, or track events, sticking with stock rubber initially is likely just fine, they'll be more forgiving and you'll learn more. If that's the case, once you've progressed through the learning curve to where the tires have become a limiting factor to progressing further, then that's a good time to step up to a higher-performance tire. If you have some track driving experience already, you no doubt already have a sense what you're looking for in tires, performance-wise.