Please help with Tire offset

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cuda guy

cuda guy

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Hi everyone

Another question

We installed a b body BB rear end from the late 60,s in our 1971 Demon when we did the measurements this is what we found

From the front of the drum to the lip of the rim we have 3 x 3/4 inches

My question is what offset should I use

We tried a rim off a 2007 Dodge Magnum RT it looked like it would need to roll the lip

Im thinking about trying to find an 8 1/4 rear end
 
I guess it depends what your intended use will be. Like old school big and littles, Tucked in or out. Tire size etc. Demons and Dusters have a generous wheel well compared to a Dart. My 73 Duster has a B-body 8 3/4 with 275-60-15s and Knockoff Ansen slots for that Arlen Vanke 70s look. They measure 15x8 with a 4 1/2 inch back space and give me the look I wanted. Yes the fenders are rolled but that's the way I got the car. SS springs round it out so the fender Mod was not really needed, Oh Well. I could have went with more BS like 1 inch more with tire to spring clearance still good. With that it would be a special order rim, and more $$$ and wait time. Off the shelf rims for this app are limited but possible. Next step is under chassis headers to get rid of the 14s in front for the Hooker fender wells.

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I "think", if I recall correctly those rear ends are within three quarters of an inch a lot of people use the three and a half inch or 4-in backspacing
 
george joseph reid said:
I guess it depends what your intended use will be. Like old school big and littles, Tucked in or out. Tire size etc. Demons and Dusters have a generous wheel well compared to a Dart. My 73 Duster has a B-body 8 3/4 with 275-60-15s and Knockoff Ansen slots for that Arlen Vanke 70s look. They measure 15x8 with a 4 1/2 inch back space and give me the look I wanted. Yes the fenders are rolled but that's the way I got the car. SS springs round it out so the fender Mod was not really needed, Oh Well. I could have went with more BS like 1 inch more with tire to spring clearance still good. With that it would be a special order rim, and more $$$ and wait time. Off the shelf rims for this app are limited but possible. Next step is under chassis headers to get rid of the 14s in front for the Hooker fender wells.

View attachment 1716069166

View attachment 1716069167
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Ironracer said:
I "think", if I recall correctly those rear ends are within three quarters of an inch a lot of people use the three and a half inch or 4-in backspacing
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1 1/4 per side
with that would I not need 6 ichs back spacing
 
cuda guy said:
1 1/4 per side
with that would I not need 6 ichs back spacing
Click to expand...
I know the E-body rear end is the widest other than probably C bodies, it is a possibility different B body rear ends are different lengths...., in fact I remember something about that! I've got a large bolt pattern 8 and 3/4 in my 74 Duster, that car never came with one of them I think it should be body but it's got plenty of room I'm running 295 50 15s w/ SS Springs. Offset on the rims is wrong, for my taste, BUT, they only stick out past the wheel well about three quarters of an inch and then I have an inch and a half to the from the tire to the springs on each side I'm sure someone with more knowledge than us will pipe right in and uncloud this for us lol. I had a list of all the different rear end links and someone even posted one on here last week I want to see it was out of the Mopar chassis manual
 
Ironracer said:
I "think", if I recall correctly those rear ends are within three quarters of an inch a lot of people use the three and a half inch or 4-in backspacing
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Mine is a 68 -70 housing and the 66-67 are a wee bit narrower, Spring perches I cant remember off the top of my head but should be close for an A-body. If not just move them. All of this is in a sticky some where.
 
george joseph reid said:
Mine is a 68 -70 housing and the 66-67 are a wee bit narrower, Spring perches I cant remember off the top of my head but should be close for an A-body. If not just move them. All of this is in a sticky some where.
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Yessir, maybe in the drivetrain section? Or axle and rear end? I know I had about 30 years ago, but I definitely seen it posted here in the last week!
 
Good grief guys. It's right here... An accurate 8 3/4" rear axle width list

8 3/4" Rear end widths, drum-to-drum:

A-BODY
  • '66-'72= 57 1/8” (or 57 13/16” for BBP axles and brakes)
    • BBP 8.25/7.25= 56 3/4”
B-BODY
  • '62-'63= 58 1/2" (And '64 Max Wedge)
  • '64 = 60 7/8" (Exc.Max Wedge)
  • '65-'67= 59 1/2"
  • '68-'70= 60 1/8"
  • '71-'74= 63"
  • '71-'73 wagon= 64 3/8"

So, it really depends on which "B-body" rear end you have. And no, it's not like a "3/4" per side, since we can pretty much rule out the 63 or 64 rear end. The narrower 65-67 B-body rear is still 1 3/16" wider per side than an A-body 8 3/4. And the 68-70 B rear is a full 1.5" per side wider.

Can you run a B-body 8 3/4 in your Duster/Demon/Dart Sport? Absolutely. I have one in my '74 Duster, and I run 18x10's with 295/40/18's. But I have a 1/2" spring offset, the quarter lips are trimmed back, rolled and pushed, and my 18x10's have a 7" backspace (+38 offset).

So what offset should the OP run? Beats me. I'd need to know which B-body rear axle is in the car, if the springs are in the stock locations or if someone didn't move the B-body spring perches and pushed the spring out reducing clearance. And of course what wheels the OP would actually like to run. But for a ballpark, it's pretty simple. Most Dusters/Demons/Dart Sports with an A-body 8 3/4 run a 15x8 with about 4.5" of backspace. So, if it's a 65-67 B rear you need more like 5 11/16" of backspace, and if it's a 68-70 it should be more like 6" of backspace. Of course, if it's a 71+ B rear all bets are off.
 
72bluNblu said:
Good grief guys. It's right here... An accurate 8 3/4" rear axle width list

8 3/4" Rear end widths, drum-to-drum:

A-BODY
  • '66-'72= 57 1/8” (or 57 13/16” for BBP axles and brakes)
    • BBP 8.25/7.25= 56 3/4”
B-BODY
  • '62-'63= 58 1/2" (And '64 Max Wedge)
  • '64 = 60 7/8" (Exc.Max Wedge)
  • '65-'67= 59 1/2"
  • '68-'70= 60 1/8"
  • '71-'74= 63"
  • '71-'73 wagon= 64 3/8"

So, it really depends on which "B-body" rear end you have. And no, it's not like a "3/4" per side, since we can pretty much rule out the 63 or 64 rear end. The narrower 65-67 B-body rear is still 1 3/16" wider per side than an A-body 8 3/4. And the 68-70 B rear is a full 1.5" per side wider.

Can you run a B-body 8 3/4 in your Duster/Demon/Dart Sport? Absolutely. I have one in my '74 Duster, and I run 18x10's with 295/40/18's. But I have a 1/2" spring offset, the quarter lips are trimmed back, rolled and pushed, and my 18x10's have a 7" backspace (+38 offset).

So what offset should the OP run? Beats me. I'd need to know which B-body rear axle is in the car, if the springs are in the stock locations or if someone didn't move the B-body spring perches and pushed the spring out reducing clearance. And of course what wheels the OP would actually like to run. But for a ballpark, it's pretty simple. Most Dusters/Demons/Dart Sports with an A-body 8 3/4 run a 15x8 with about 4.5" of backspace. So, if it's a 65-67 B rear you need more like 5 11/16" of backspace, and if it's a 68-70 it should be more like 6" of backspace. Of course, if it's a 71+ B rear all bets are off
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And thats to flange not drum to drum? One of my buddys owns Cars for the Stars, he's been cutting up flipping and selling and building Mopar cars for as long as I've known him he told me it was 3/4 of an inch per side so I took his word on it. My Bad, I guess...
 
Ironracer said:
And thats to flange not drum to drum? One of my buddys owns Cars for the Stars, he's been cutting up flipping and selling and building Mopar cars for as long as I've known him he told me it was 3/4 of an inch per side so I took his word on it. My Bad, I guess...
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I posted “drum to drum” specs, in this case that’s wheel mounting surface to wheel mounting surface. Outer surface of the drum. The “flange to flange” numbers are the axle housing flange, not the axle flange.

Somebody probably halved the “per side” measurement. Or they’re comparing an A-body 8 3/4 rear end with BBP axles to a 65-67 B rear, that’s under an inch per side but still more than 3/4”. But that’s back to which B body rear you’ve got.
 
72bluNblu said:
Good grief guys. It's right here... An accurate 8 3/4" rear axle width list

8 3/4" Rear end widths, drum-to-drum:

A-BODY
  • '66-'72= 57 1/8” (or 57 13/16” for BBP axles and brakes)
    • BBP 8.25/7.25= 56 3/4”
B-BODY
  • '62-'63= 58 1/2" (And '64 Max Wedge)
  • '64 = 60 7/8" (Exc.Max Wedge)
  • '65-'67= 59 1/2"
  • '68-'70= 60 1/8"
  • '71-'74= 63"
  • '71-'73 wagon= 64 3/8"
Click to expand...

This comes up so often, the info above ^^^ should be a sticky at the top of this section.

When I converted my A-body 8-3/4 to shortened C-body axles, i carefully dropped a plumb bob to the garage floor and marked both sides. The bigger axles added exactly 3/8" to the track on both sides measured from the axle face, not the drum face. So I agree with your 57-13/16" dimension. The A-body drum face thickness may actually be thinner than the bigger drums too.

People always seem to want to stuff the biggest tires they can get away with. (I just bought a /6 70 Dart, what's the biggest tire I can fit?)
These little quarter inch increments here and there can add up. The old Direct Connection books said there can be a half inch difference from side-to-side on the same car.
 
Ironracer said:
And thats to flange not drum to drum? One of my buddys owns Cars for the Stars, he's been cutting up flipping and selling and building Mopar cars for as long as I've known him he told me it was 3/4 of an inch per side so I took his word on it. My Bad, I guess...
Click to expand...
Drum to drum sorry
I'm thinking about a positive offset rim newer style
 
cuda guy said:
1 1/4 per side
with that would I not need 6 ichs back spacing
Click to expand...
They make a real nice and cheap tool that lets you simulate your wheel specs. eBay has them for like 50 bucks
 
cuda guy said:
yes that looks fantastic
what rims and tires are they
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Here ya go, talk to this guy

Just be sure you guys discuss adapters or something

www.forabodiesonly.com

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KosmicKuda said:
This comes up so often, the info above ^^^ should be a sticky at the top of this section.

When I converted my A-body 8-3/4 to shortened C-body axles, i carefully dropped a plumb bob to the garage floor and marked both sides. The bigger axles added exactly 3/8" to the track on both sides measured from the axle face, not the drum face. So I agree with your 57-13/16" dimension. The A-body drum face thickness may actually be thinner than the bigger drums too.

People always seem to want to stuff the biggest tires they can get away with. (I just bought a /6 70 Dart, what's the biggest tire I can fit?)
These little quarter inch increments here and there can add up. The old Direct Connection books said there can be a half inch difference from side-to-side on the same car.
Click to expand...
It's stickied at the top of the drivetrain forum

cuda guy said:
yes that looks fantastic
what rims and tires are they
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cuda guy said:
Sorry but they wont fit i need 114.3 but thanks again
Click to expand...

Yeah exactly, those are 5x100 so they're not right for either A-body bolt pattern.

I run Enkei RPF1's on my Duster, they're available in 5x114.3 and in a bunch of useful offsets. What you need will depend on which B-body rear axle you have though, so you'll need to measure. There are a lot of options in 18x9" and 18.9.5".



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