Backspcing question for you big wheel guys

[Nu2Mopar]

I am trying to figure out the proper backspacing for wheels. I am building a 70 duster, front disc and rear drums, stock wheel wells. I am going with 18x7 in front and either 19 or 20x8.5 in the rear. Does anybody know the proper bs for these cars / wheels and any suggestions on tire size would be helpful as well. I was figuring on a 225/40 in front and a 255/40 or 35 in the rear??


I have searched but there seems to be alot argument on the subject...lol

 

[moparpollack]

Steve,

What brakes and what size brakes are on the front? What rear end do you have? is it an a body or b body?

 

[pauly v.100]

i have 17x8 cobra wheels for now that have 5.72 backspace. the fronts with that backspace would work fine for you but the backs need spacers to work with a stock dimension A-body rear end. mine's from a B-body so they fit perfect. I've seen other members cars here that are running 17-18 inch wheels with lesser backspace, maybe 4.5-4.75 that seem to have pretty good luck, I plan to go bigger but i won't spend a penny on new rims without making sure they will fit first so i'm going to blow a few bucks and buy a Percy's wheelrite tool for gettin it right.
I'm hoping to squeeze a 9.5 wheel and tire on the back without spring relo or tubs.

 

[Nu2Mopar]

i was thinking 4.5" bs in front? and maybe a 5.25 bs in rear? I have not tried any measurements yet, but will soon. Thoughts?

 

[moparpollack]

The bigger rim diameter makes it possible for more backspacing in the front. This keeps the tire out of the fender well. Upgrading to the 12" discs allows you to bolt on the 5.72 backspace mustang wheels. If you run a b-body rear end you can also run the 5.72 backspace wheels so you can rotate the tires.