So what would be the correct backspacing to put some 17x8 on my 73. I have upgraded to the 12" cop discs. A friend ordered 16x8s for his Duster once and we raced down to pick them up, also picked up a $1500 "speed contest" ticket on the way, when we got there the geniuses at Goodyear had ordered for big bolt pattern. He spent the rims money paying off the ticket

Ma Mopar usually used 0.5 inches of offset in her designs. So a 8 inch rim would be 5 inches of backspacing (4 inches of front spacing) to get you a 0.5 inch offset.

That should be close but the only way to know for sure is to mock it up and move the wheel through the entire travel. You'll need the OEM style of upper ball joint since the aftermarke ones will hit on rims with a lot of backspacing. You'll also want to pay attention to the outer tie rod joint since that will sometimes hit on rims with a lot of backspacing. Usually a 17 inch rim is big enough though to clear the tie rod.

Someone correct me if I am wrong, but IIRC-

0.5" of negative offset on an 8" wide rim would leave 3.5" of backspacing and 4.5" of "front" spacing.

I know this is apples/oranges, but my truck came from the factory w/ 6.5" wide rims and 0.5" of positive offset, giving a 3.5" backspacing and 3.0" frontspacing. My new rims are 8.5" wide, and have 3.5" backspacing (0.75" negative offset) and 5" frontspacing. In effect, the backside of the rim stayed in the same place while the front side of the rim moved out 2" (and actually fill up the fenderwells now)

'73--easiest way to find the correct backspacing is to take a few measurements on the stock rims, backspacing is going to be the most important number if you don't have much clearance behind the wheel.

-S/6

_________________
The "Silver Bullet"
87 Ram D150

Backspacing is typically measured from the back of the rim, not the bead seat. The outside measurement on a typical steel rim is 1 inch wider than the bead measurement. Therefore, a 8 inch rim measures 9 inches across. That is why the backspacing would be 5.0 and the front spacing would be 4.0 on a 8 inch rim with .5 inch of offset.

I see--Thx Andy

-S/6