i'm on 18" (225x40) wheels and its not really all that bad still using sports pack suspension, even on Irish roads (and thats saying something!)
i do agree that depending on the spoke design, you may need bigger brakes (im upgrading to the brembo 305 GT kit)
strength is really key when your running bigger wheels / smaller sidewalls
http://i36.photobucket.com/albums/e1...g?t=1171663894
http://i36.photobucket.com/albums/e1...g?t=1171664162