yes, they'll rub, those are f'ing huge for the m3.
you MIGHT be able to get away with 235 or 245 in a 40 profile 19". 255/40 will be way too tall in a 19. 255/40 works in 18 but not 19.
245/40R19 would likely work on the rear but not on the front. you could do 225/40R19 front (e46 m3 front oem 19) and 245/40R19 rear and have narrower than stock but i doubt you want that for tires are not dedicated snows
tire construction matters a lot more than 5 % points of sidewall profile. a Continental DWS in 255/35R19 275/35R19 will ride SIGNIFICANTLY smoother and softer than a PS2/PSS in that sizing
Last edited by smmmurf; 09-22-2012 at 08:40 PM.