15" wheel?

[1fastGN]

I did some searching and found a lot of info on 16, 17, and 18" tire combos but not much on 15".
I'm looking at 15X6 and 15X8 welds for my 89 LX. what would the proper offset/backspacing need to be.
would like to run a 275/50 on the back and prolly a 225/60 on front.

 

[90stang5speed]

for the rear, 8x5.5 back space worked well for me. I also had 275 50 15 drag radials. My quad shocks were removed and fenders were rolled before I bought the car though.