Backspacing still doesn't make sense to me.
Maybe I can help Jerry. I switched over from the original Rallye wheels to Cragar SS on my 71 Demon last year. Firstly, the rear end is a stock 8 3/4 in the stock location along with the springs. I went with Cragar SS 15X7 with 255/60x15"s Bf Goodrich TA (banana skins) and the clearance between the leaf springs and tire side wall is 1/2". The clearance between the outer side wall and inner wheel well is 3/4". The reason I went with the 15x7's (4 1/8" backspace) and not the 15x8's (4 1/4" backspace) is the that tire sidewall would have been to close to the leaf springs. The section width (sidewall to sidewall) of these tires on a 7 inch rim is 10" whereas that section width changes to 10.5 with a 8 inch rim. Tire section width changes by approx. .25" for every .5" change in rim width according to Goodrich. The end all be all is that if I used the 8" SS rims the clearance between the tire inner sidewall and the leaf springs would have been 1/8 to 1/4 inch which is getting way to tight especially with flexible radial sidewalls.
Maybe I can help Jerry. I switched over from the original Rallye wheels to Cragar SS on my 71 Demon last year. Firstly, the rear end is a stock 8 3/4 in the stock location along with the springs. I went with Cragar SS 15X7 with 255/60x15"s Bf Goodrich TA (banana skins) and the clearance between the leaf springs and tire side wall is 1/2". The clearance between the outer side wall and inner wheel well is 3/4". The reason I went with the 15x7's (4 1/8" backspace) and not the 15x8's (4 1/4" backspace) is the that tire sidewall would have been to close to the leaf springs. The section width (sidewall to sidewall) of these tires on a 7 inch rim is 10" whereas that section width changes to 10.5 with a 8 inch rim. Tire section width changes by approx. .25" for every .5" change in rim width according to Goodrich. The end all be all is that if I used the 8" SS rims the clearance between the tire inner sidewall and the leaf springs would have been 1/8 to 1/4 inch which is getting way to tight especially with flexible radial sidewalls.
