Zr1bandit

What's the proper setback for a 15x8 and 15x7 wheel on a 1970 olds 442. I see there are different option out there ----thanks ----Greg

joe_padavano

Setback?

Do you mean backspace? Or offset?

In any case, the offset should be near zero. To get that means about 3.75" backspace on a 7" wide wheel and about 4.25" backspace on an 8" wide wheel.

Zr1bandit

Yes, backspace is what im looking for -----thanks

Qwik71442

15x7 4" Backspace
15x8 4.5" Backspace

orange442

These sizes and backspace measurements above center the mounting surface dead center of the wheel and work well for our cars. It is also referred to as zero offset. When you measure wheel width you measure inside bead to inside bead but when you measure for backspacing or offset you measure from the wheel to hub mounting surface to the outside lip. With the wheels above as an example, a 15x7 wheel will measure right around 8" lip to lip so 4" backspace is also "0" offset because the mounting surface is centered in the wheel. Offset can be confusing to many because if a wheel is not zero offset then it is measured negative or positive in millimeters so you just need a good conversation table or a good understanding of millimeters to inches! Example: a 15x8 with a + 25 mm would be about 5.5" backspace. Since zero offset for a 15x8 is 4.5", and 25 mm is just a hair shy of 1" that gives you the 5.5" measurement. Learning this will help when looking at new wheels because many will have offset measurements but may not give you the backspace measurements.