a 16x8 with 4" backspacing will put the tire out of the fender your inch to 1 1/2". I have 285's on 8" and do not have any rub at full lock on level gound. A true 12.50 may be a little closer to rubbing, but since you are asking about a 2500 (taller frame) I think it will be fine. Some people have said that the 2500's clear 35's.