I have a 72 Malibu, and I'm getting a set of Boss 338's, 18x8's for the front and 20x10's for the back. I hope to run 235/45R18 tires on the front and 275/40R20 tires on the back. Can anyone tell me the appropriate backspacing for this configuration? My suspension is stock or very close to it.

I have a 72 Malibu, and I'm getting a set of Boss 338's, 18x8's for the front and 20x10's for the back. I hope to run 235/45R18 tires on the front and 275/40R20 tires on the back. Can anyone tell me the appropriate backspacing for this configuration? My suspension is stock or very close to it.


4.5" backspace on the 18x8's and 5.5"-5.75" for the 20x10's. However,the Boss 338 20x10's for a 5x4.75 bolt circle wheel have 6.25" backspacing.

4.5" backspace on the 18x8's and 5.5"-5.75" for the 20x10's. However,the Boss 338 20x10's for a 5x4.75 bolt circle wheel have 6.25" backspacing.

I can get 20x8.5's on the rear, what backspacing should i use then? They offer a 5.24 and a 5.79.

Their 20x8.5's for a GM car have 5.239" of backspacing which is still excessive for that width. Zero offset for an 8.5" wide rim is 4.75" backspace which is almost 1/2" more than you really need. What you could do is this;run a 1/4" thick disc brake spacer between the hub and wheel for a corrected backspace of 4.989". Stick a 255 width tire on there and you should be good to go.

Their 20x8.5's for a GM car have 5.239" of backspacing which is still excessive for that width. Zero offset for an 8.5" wide rim is 4.75" backspace which is almost 1/2" more than you really need. What you could do is this;run a 1/4" thick disc brake spacer between the hub and wheel for a corrected backspace of 4.989". Stick a 255 width tire on there and you should be good to go.

Alright, thank you very much for your help. I feel confident that I'm gettin the right stuff now :yes: