Backspacing question

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BigBlockMopar28

BigBlockMopar28

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I have a 74 swinger with an a body 8 3/4, factory length axles, and s/s springs. What kind of backspacing would i need to run a 10 wide wheel with a 10.5 wide, 26 tall tire? Thanks
 
On my car I only have 11" from inner fender to the spring. Centering a 10.5 in tire in there would be a bear, and really I'd want at least .5 clearance on each side. Im sure it isn't the answer you want, but best to get in there with a tape and square and measure her up.
 
Bolt a flat on the hub and make some measurements....


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Unless you've got 1/2" offset springs you're not going to get a 10.5" wide tire in there. Not gonna happen. You need at least a 1/2" to the quarter minimum, and about that much to the spring unless you're running larger diameter rims. So, with most Darts having about 11" from quarter to stock location springs it's not gonna work.
 
4.5 back space, 8" rim should get close.
Not sure of your year, however.
Have 275 50 15 on 67 cuda.
 
72bluNblu said:
Unless you've got 1/2" offset springs you're not going to get a 10.5" wide tire in there. Not gonna happen. You need at least a 1/2" to the quarter minimum, and about that much to the spring unless you're running larger diameter rims. So, with most Darts having about 11" from quarter to stock location springs it's not gonna work.
Click to expand...
Show him my old pics
;)
 
Move springs, like blu says.
Then I'm guessing, a 6" bs, add a spacer as required
I run a 10 inch rim and over a 13" section with a 4.5 BS on a 3" narrowed rear. So that's the flanges moved in 1.5 per side. And 1.5 plus 4.5 = 6
IMO that's not pretty on a Mopar.
You want a 10 in there? My best advice is to move the springs,narrow the rear, and measure it up, for custom wheels. Then prepare for some massaging in certain areas.
Or you could go oldschool............but you'll get no help from me,lol.
 
Thanks for the input guys. Due to my lack of self trust as far as cutting and welding to move the spring peices on the rear, ill stick to measuring and seeing what i can fit in there. Hopefully i can atleast get a 9.5 with an 8 wide wheel? I dont know, ill have to do some research looks like.
 
Quick question: what about a 15x8 wheel with 4.5" backspacing with a 9.5 tire? Anyone see any potential issues with that as far as width issues? As you can see im a newb when it comes to this stuff. Thanks!
 
BigBlockMopar28 said:
Quick question: what about a 15x8 wheel with 4.5" backspacing with a 9.5 tire? Anyone see any potential issues with that as far as width issues? As you can see im a newb when it comes to this stuff. Thanks!
Click to expand...
Why not use offset spring hangars, and roll the outer lip before u try to measure anything ? U can very carefully cut a rear spring pad in half, (DID MINE ONN A BIG BAND SAW) and weld half of it to each side of the existing pads on the axle. u won`t have to mess w/ getting it right or out of whack. u then redrill the u bolt holes for the offset, the rest is bolt together stuff. U could end up w/ about 1 3/4" more room. I did it and have 295 65 15 drag radials on a 68 barracuda , which have very small wheelwells to start with. I did lengthen the front edge of the wheel well before paint tho for the tire heighth .
 
mycuda said:
4.5 back space, 8" rim should get close.
Not sure of your year, however.
Have 275 50 15 on 67 cuda.
Click to expand...

famous bob said:
Why not use offset spring hangars, and roll the outer lip before u try to measure anything ? U can very carefully cut a rear spring pad in half, (DID MINE ONN A BIG BAND SAW) and weld half of it to each side of the existing pads on the axle. u won`t have to mess w/ getting it right or out of whack. u then redrill the u bolt holes for the offset, the rest is bolt together stuff. U could end up w/ about 1 3/4" more room. I did it and have 295 65 15 drag radials on a 68 barracuda , which have very small wheelwells to start with. I did lengthen the front edge of the wheel well before paint tho for the tire heighth .
Click to expand...

What fits a Barracuda will NOT fit a Dart. Barracuda's have more room than a Dart does, by about an inch. It's all on the quarter side, as the frame rails and axle width is the same. But just like Demons/Dusters/Dart Sports the Barracuda has a wider outer wheel tub. So, not relevant to a Dart Swinger. Even less relevant because the Dart's have such a low wheel opening. You can't hang the tires out past the quarters on a Dart. Well, maybe if you installed a 6" lift kit or something. But not on anything even close to stock ride height. On a Barracuda you can fit 275's without moving the springs at all. The absolute widest tire you can fit on a Dart without moving the springs a 255, and most Dart's can't even manage that without rolling the quarter.

BigBlockMopar28 said:
Quick question: what about a 15x8 wheel with 4.5" backspacing with a 9.5 tire? Anyone see any potential issues with that as far as width issues? As you can see im a newb when it comes to this stuff. Thanks!
Click to expand...

You're moving in the right direction. Do you have BBP axles? Because that changes the backspace you're going to need. I know you said you have an A-body 8 3/4, but factory axles would be SBP.
 
And 255s have about a 10" section on a checking rim of 7 inches. But they need at least an 8" rim to handle and wear decently. That would likely bring the section width to 10.5.No problem overall
With a zero offset wheel this would be a 4.5 bs, no problem on the inboard side, but into the outer wheelhouse on the outboard side.Ouch
Ima thinking you might make that work with a 5.75 bs, but it would be tight.
Blu?
Don't be thinking of running that 255 on a 7"rim to tuck it in. You will have to reduce the tire pressure to something like 24psi, to make it run flat to the road. That works in a straight line. But the first time you run it around a turn at 30 mph with the power on, you'll be in for a nasty surprise; namely rear-steer! This is when the tire-tread rolls under the car,taking the sidewall with it. Sidewalls do not take kindly to that abuse. They're only 2 plys and have no carcass protection
 
72bluNblu said:
What fits a Barracuda will NOT fit a Dart. Barracuda's have more room than a Dart does, by about an inch. It's all on the quarter side, as the frame rails and axle width is the same. But just like Demons/Dusters/Dart Sports the Barracuda has a wider outer wheel tub. So, not relevant to a Dart Swinger. Even less relevant because the Dart's have such a low wheel opening. You can't hang the tires out past the quarters on a Dart. Well, maybe if you installed a 6" lift kit or something. But not on anything even close to stock ride height. On a Barracuda you can fit 275's without moving the springs at all. The absolute widest tire you can fit on a Dart without moving the springs a 255, and most Dart's can't even manage that without rolling the quarter.



You're moving in the right direction. Do you have BBP axles? Because that changes the backspace you're going to need. I know you said you have an A-body 8 3/4, but factory axles would be SBP.
Click to expand...
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Not implying that they are the same, most old mopars aren`t the same -even in the same body style sometimes. What I was getting at, u can do the offset spring hangar thing which is pretty easy the way I described, and it will give u about the most tire clearance u can get w/o major surgery. But suit yourself, keep asking and -----------------
 
famous bob said:
Why not use offset spring hangars, and roll the outer lip before u try to measure anything ? U can very carefully cut a rear spring pad in half, (DID MINE ONN A BIG BAND SAW) and weld half of it to each side of the existing pads on the axle. u won`t have to mess w/ getting it right or out of whack. u then redrill the u bolt holes for the offset, the rest is bolt together stuff. U could end up w/ about 1 3/4" more room. I did it and have 295 65 15 drag radials on a 68 barracuda , which have very small wheelwells to start with. I did lengthen the front edge of the wheel well before paint tho for the tire heighth .
Click to expand...
Famous Bob are your tires tucked inside wheel wells?
 
duster2 said:
Really , I thought 255-60-15 tires worked well on a 15 x 7 wheel. Hmmmm !!!

Frank
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A 15x7 is the minimum recommended width from the manufacturers for a 255/60/15. The manufacturers measuring rim width is only 15x7.5” though, and the tread width is usually ~8” to 8.5” depending on which tire you’re talking about.

Obviously there are some tire shape differences between the minimum recommended width and the maximum recommended width. But as long as you’re still in the manufacturers recommendations you really shouldn’t have any issues. Maybe some tire pressure fine tuning for the track, but even that should be minor.

Based on the number of people here that completely ignore the manufacturers recommended minimum and maximum width and raise holy hell about how they’re not dead any time I say something about not doing something stupid like ignoring the minimum rim width recommendations I’d say you should be fine if you follow the manufacturers guidelines.
 
The people that insist on putting a 275-60-15 on a 15 x 7 wheel or a 295-50-15 on a 15 x 8 wheel , not good.
Just because you can , don't make it right.

Frank
 
BigBlockMopar28 said:
Quick question: what about a 15x8 wheel with 4.5" backspacing with a 9.5 tire? Anyone see any potential issues with that as far as width issues? As you can see im a newb when it comes to this stuff. Thanks!
Click to expand...
It wouldn't fit on my '69 GTS. Absolute max is a 235 tire which is about 9.25" depending on what wheel you use. I'd say try 15x7 with 4 1/2 BS, you may need some 1/8" or 1/4" spacers to fine-tune it. Of course it also depends on how high the rear end is sitting. The other thing that truly sucks is that both sides of these cars are seldom the same!
 
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