Well, what width are your rims?
Your rims are made for 255?? They're 9" wide then?
Also, just as a note, by running wider tires in the rear compared to the front, you will make your car understeer more.
I've seen 255's on stock 8.5" M3 lightweight rims, they fit if the car isn't dropped too much, but they bulge out a lot, the contact patch is practically the same as a 245 (and the 245's are lighter and cheaper).
"Driving is like a narcotic, an addiction that can take over lives. It ruins people, breaks families apart, and even kills. Itís habit that needs to be fueled. Time, money, rationality, sweat, knuckle skin, and anyone who disapproves are of little importance to a driver, and are often overlooked. Hi, Iím Nelson, and Iím a drivaholic."