I have a 65 mustang with a 15x8 with a 4 inch backspace and I have about 1 1/2 space in the rear part of the tire before it touches the leaf spring and I have about 2 inches in the front. I hav e about 3 inches before it touches the inner fender wheel. I also have a 2inch flare on the car. On the Dodgestang site they put a 15x9.5 with a 5 inch backspace on a 65 mustang. What has been the largest rim has someone put on the rear without tubbing it or putting spring relocation kits?