re: aftermarket wheels - if you go with a reputable outfit like tirerack you should be ok. they don't sell anything that doesn't have SAE on all the proper letters of certification attached. also, they do their homework with offsets and clearances and i never even worry about it. OTOH if you go and buy your wheels from costco or pep-boys - you're on your own. for that matter, my brother traded in a set of 560 alloys for another oem set that had been chromed and got a big headache instead. he got a harmonic vibration at speed and after numerous trips to have balance & alignment checked it turned out that the wheels were out of true! so indeed, buyer beware...