I am considering using 15 x 7 wheels with 4 1/4" backspace. I am assuming 215/70/15 tires (26.9" diameter) will fit front and back without rubbing? What about 225/70/15? (27.4" diameter). I don't think I can go any wider due to the clearance at the rear fender lip.
I've got 255/60-15 on 15x7 Buick rallys with 4-3/8" backspace. It might rub at times on cars where the rear isn't perfectly centered.
I don't really know, I've never tried it. I think it would be really tight in the rear with the wheels i'm running.
I currently run a 255 50 17 on the rear of my 67. 10.5 wide wheels. I did have to trim the outer wheelwells a lil bit. Note that car sits down low on the setup all tucked under the fender.
Widest tires I've been able to put on my '67 is a P255/60-15 which are mounted on 15x8 Weld wheels with over 5" backspacin. One side would occasionally rub under certain circumstances like hitting a bump while turning into a parking lot. To go any wider than P255 of my car would require some modifications or cutting.
