thanks!
also found this, courtesy of JCz4Bimmer's comments...
http://www.zpost.com/forums/showthre...ghlight=square
there's a lot of info in there about front tire and suspension setup for the ///m's. one of the posts describes needing spacers and 3 degrees of negative camber to get a 255 treadwidth to run smoothly for the front. i think it's safe to say that if you want to retain the stock sport suspension, a 235 treadwidth is safe.