Question on backspacing on rear wheels

[C.Rector]

Hello guys
I have a 73 Duster and am looking to use 15x8 rallies on the rear with a 235 or 245 60 rear tire. Im having a hard time determining if I should use a wheel with 4 inch back spacing or one with 4 1/2 inch backspacing. I dont want to run any type of air shock or air suspension just simple rear set up with no tire scrub.
Also I have found one company that sells the rally wheels new but they only offer a 15x8 with a 51/2 back spacing. Any idea on who sells these wheels?
Thanks in advance
Chris

 

[Divenut]

I believe 4 1/2 is what most folks use/suggest. But I would guess either 4 or 4 1/2 would work with the relatively small tires you're planning to use.

Pat

 

[72bluNblu]

I have 15x7" cop rims on the back of my '74 Duster, they have a 4.25" backspace. Not a whole lot of room to the spring, I'd say no more than a 1/2", and I only run 225/60/15's. I would say that 4.5" of backspace is as much as you can comfortably run without a spring offset or spacers. Some cars might be able to get away with more, but it won't be much more.

 

[Dodge74]

I have 15x7" cop rims on the back of my '74 Duster, they have a 4.25" backspace. Not a whole lot of room to the spring, I'd say no more than a 1/2", and I only run 225/60/15's. I would say that 4.5" of backspace is as much as you can comfortably run without a spring offset or spacers. Some cars might be able to get away with more, but it won't be much more.

can we see some pics...................

 

[72bluNblu]

Sure. Pictures show the spacing to the spring. As you can see, plenty of room to the quarter still. But only 1/2" to the spring, if that.

With a 15x8 you can run 4.5" of backspace without issue, maybe even 5" because of the way that the backspace measurement works, a 15x8" with a 5" backspace should end up about .3" closer to the springs than the 15x7" with 4.25" spacing. But 5.5" backspace would move the tires in .8" from where mine are, and as you can see there isn't that much room. You'd need spacers to manage that.