Back space question

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gunmetal72

gunmetal72

Life is a dark ride
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This might have been asked before.
My 72 Duster has 3.5" backspace rims on the rear. Tires are 245 60 x 15" T/A's and I would like put them on a wider rim. Need to know if will a rim with a 4" back space will work without the tires rubbing the springs before I buy them. Anyone have any thoughts?
 
There was plenty of room. Take a piece of wood against the drum and measure the outspacing. I had 275/60/15's on it and I think I had more room to the outside still. The 1/4's bow out on Dusters where other cars are straight
 
Ya, I am not concerned with clearance on the 1/4s, just the room between the tires and the rear springs
 
As sedan mentioned, the Duster has more clearance back there than other a-bodes. I have seen many get a 275/60/15 under there with ease. Your fitment will depend on several things (many that were already mentioned). Ex: rim size & offset, tire size (and sidewall bulging .. if any) and the one thing many forget to do and that is to take measurements on both sides. This is more important if you are trying to max out your tire/wheel combo. Ma Mopar is known for not being dead nuts centered with their rearend assemblies. I've seen some serious variances.

As for the 8" rims, I think you would be ok with the stock offset and your 245s. If you went to something like a 275, then just take some measurements. If your rearend is centered, you should be good to go. I have the 15x8 steelies with 275/60/15s on my '69 Barracuda. Just to get a hair more clearance, I used the offset shackles which move the springs inboard .8" and then I cut the centers out of the 15x8s and moved them .75" for a 4.75" BS. They fit nicely. Also, I centered my rearend assembly. It was off approx. 3/4". God luck.
 
OK, you have 7" rims with 3.5" BS. With a 1/2" added for the 4" BS and a 1/2" added for a 8" rim that should makes the tire 1" closer to the spring IMO. So if you have a 2" to the spring right now you should be good.
 
I 15×7 rallys out back of my dart sport. It has an 8.25 rear. Backspace is 4.25. Fit good but not out far enough for my taste to fender. If i use 15×8 rallys and 4.125 or even 4 inch backspace will wheel come out more?
 
What rear axle? BBP or SBP?

8.25's are about an inch narrower than 8 3/4's, so that changes what backspace will clear by almost half an inch.

A BBP A-body 8 3/4 can take up to about 5.25" of backspace. Even SBP can take up to about 5" of backspace.

BBP 8.25 and you'll want more like 4.75" backspace to max out the tire width if the springs are in the stock location.
 
QuickDart360 said:
I thought the lower the # on backspace the further out towards fender wheel went?
Click to expand...

Yes, that's true.

The numbers I listed are the maximum amount of backspace you can run before you start running into spring interference. They will also allow you to run 275's on a duster with the stock spring locations and no cutting or rolling of the quarters. At least on most cars.

If the tires are narrower than that you can run less backspace and still clear, just depends on what tires you want to run. But it you run rims with less backspace you're also committed to narrower tires, you won't have the clearance to go to wider tires without changing the rims.
 
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ok, tires are 245 60 x 15 -
will a 15" x 8" rim with 4" backspace work
or
should I use the 15" x 7" rim with a 4" backspace.
Only other option I have for the rims I want is 15 x 8.5" rim with a 3.5" backspace, not sure what the tires will look like with this rim
 
If those are the choices I'd use the 15x7's with a 4" backspace. That's a zero offset rim and will locate the tires best. You won't have a ton of space to the quarter but they'll fit.

The 15x8's with a 4" backspace are a -12 offset, so the tires will stick out an extra 1/2". Unless your car sits pretty high in the back you might have to trim the quarter lips to keep those from rubbing if you have a BBP axle 8 3/4.

The 15x8.5's won't clear the quarters.
 
ok, thanks, that is what I was kinda thinking, going from a 6" rim to a 7" should make the tires look a lot better.
I have the SBP axle with 8 3/4
 
72bluNblu said:
What rear axle? BBP or SBP?

8.25's are about an inch narrower than 8 3/4's, so that changes what backspace will clear by almost half an inch.

A BBP A-body 8 3/4 can take up to about 5.25" of backspace. Even SBP can take up to about 5" of backspace.

BBP 8.25 and you'll want more like 4.75" backspace to max out the tire width if the springs are in the stock location.
Click to expand...
So a stock A-body 8 3/4, with the BBP 10 x 2.5 rear B-body brakes conversion gives a 5.25" back space? Good to know, I'm planning that swap, Thanks!
 
Thanks 72blunblu! I was a bit confused but i think 15×8 rally with 4.125 backspace will give me the right look to my ride. Since my 8.25 is narrower than the 8.75. Now i have 15×7 & 4.25. 275/60/15 tires but not quite far out to fenderwell as i like. 15×10 rally has crossed my mind no idea offset!
 
QuickDart360 said:
Thanks 72blunblu! I was a bit confused but i think 15×8 rally with 4.125 backspace will give me the right look to my ride. Since my 8.25 is narrower than the 8.75. Now i have 15×7 & 4.25. 275/60/15 tires but not quite far out to fenderwell as i like. 15×10 rally has crossed my mind no idea offset!
Click to expand...

Those will definitely be close to the quarters. But if your car sits higher than mine it might be ok. I test fit 17x9's with 275/40/17's on my Duster when I still had the stock spring locations and a BBP 7.25, which is the same width as a BBP 8.25. Those were pretty close on the spring with a 4.75" backspace, I might have needed a small spacer to actually run those, and I did have a little extra room to the quarters. Not an extra 5/8" though. You may need to cut/roll the quarter lips a little with only 4.125", it'll depend on your ride height.
 
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