I have a 77 and looking at crager keystone , could some one explane back spacing . The 15 x 8 have a 3 7/8
thanks

see if this helps you ;)

https://www.rsracing.com/tech-wheel.html

Imagine you have a 10 inch wide wheel. If the center of the wheel (spokes on a mag wheel) are in the middle of the wheel than it would have about five inches of back spacing. Back spacing is the measurement from the rear edge of the wheel to the back face of the wheel. Most people like to have a lot of wheel showing on the front to make it appear deep. That leaves little room for back spacing on some designs.

Big Dave

A 77 should take a 4.25" b.s. wheel in the front an a 5.25" b.s. wheel in the rear max! Unless the susp. has been modified.Try to stay away from rev. offset wheels they tend to make the car act strange escpecially at high speeds .A 15x8 wheel with a 4" b.s. has the hub directly in th ctr. of the rim,or very close to it .:thumbsup: