Also, what size tires will fit a 15x8 rim. Will I need to measure backspace, if so, how?

Thanks
Duff

A good explanation (with a picture) of backspace can be found at web page (http://www.yokohamatire.com/utwheels.asp). This also tells you how to measure it.

I run 255\60\R15 on a 15x8 rim with 4.5" backspacing on my 72 Chevelle. Most folks will tell you that you can go up to a 275 on that size rim and suggest a 4.5" backspace to minimize rubbing issues (at least for the 71,72 models).

What year model is your car?

1970. My desire is to fill the wheel well with height and width and not go past the edge of the fender.

i am running 28/10.5/15 mt sportsman pro with a 8in rim and 4 1/2in spacing with PLENTY OF ROOM left!!! thinking of getting 28/12/15. thats in a 68 chevelle, dont know if there is any difference in the size of the wheel well