Max Width Of Rear Wheel/tire

Stock wheel tub and stock spring locations a 255 is the absolute best you'll do, and that would require perfect backspacing. Some cars wouldn't be able to pull that off without rolling the quarter lip even with everything perfect just because of the body tolerances on these cars and the manufacturers section width variation on the tires. 245's are the better bet, and even that will require careful measurement of your car to get the backspacing right so the wheels are centered in the wells.

1/2" offset springs with stock wheel tubs and you can get a 275 on most cars, again some might need a quarter lip trim/roll and your backspacing will have to very good. With a mini-tub and 3" offset and 335's have been done. But that's a crap load of work.