15x8.5, 3.810 backspace - Vintage Mustang Forums
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post #1 of 4 (permalink) Old 06-27-2019, 04:24 PM Thread Starter
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15x8.5, 3.810 backspace

I purchased American Racing wheels in 15x8.5 for a mach1 70.
I took them to be able to have the option of mounting several tire widths. (from 225 to 255).
The problem is that I never tought about backspace so now I m doubting about the tire's size that I can mount on wheels without thez sub on the front Fender and rear quarter panel. After some research I saw that the tire size suggestion for a 15x8 rim and a 4.5 inch backspace is 225 / 60-15.
My first idea was to mount 235 / 60-15 in the front and 255 / 55-15 in the rear. But I just saw that rims have 3.810 inch backspace. Do you believe that these tire sizes still work ? What do you recommend?
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post #2 of 4 (permalink) Old 06-27-2019, 10:32 PM
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My experience with my 70 Mustang is you need about 0 offset. That would be a backspace of 4.75 since the wheel is 1 inch wider than advertised due to the bead. I have run 295/50/15 in the rear and 265/50/15 in the front with fender rolling. I'm running 275/60 and 245/60 now. The fronts rub slightly when turning at full lock and I do run lots of negative camber.
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post #3 of 4 (permalink) Old 06-28-2019, 04:58 AM Thread Starter
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Thanks for you answer. i'll check that
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post #4 of 4 (permalink) Old 06-28-2019, 11:27 AM
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I have both and the 15X8 with 4.500 back spacing is the hands down winner for clearance purposes. It pushes the tire in "just enough" versus the 15X8.5 with the 3.75 off set. Plus the 15X8 has the outside "look" of a 15X7 wheel . I wish they made a 15X10 that way.

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