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BackSpace question with a B-Body 8 ¾” in an A-Body #1714026
12/22/14 03:12 PM
12/22/14 03:12 PM
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Saint Peters, MO
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Brian Offline OP
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Here’s the deal, I want to go to a 17” x 8” wheel probably running a 235/50-17 which are 26.3” tall all around on my 1971 Duster. This size tire allows me to run modern maximum performance summer tires while still retaining enough sidewall height to look correct. Ideally I would like to run the same size wheel with the same offset (BackSpace) all around as well. I may consider larger rear tires for the track if traction is a big problem.

Since I’m also upgrading the front suspension to 73-76 spindles with 11 ¾” discs with Gen I Viper calipers that will push the front wheels out requiring a wheel with a lot of positive BackSpace; it seems that the narrow A-Body 8 ¾” rear is not wide enough and will require a much deeper negative BackSpace to push the wheels back out into the quarter Panels. If that’s the case, I can’t rotate the tires front to rear and would have to carry a generic spare tire like a 205/70-15 on a steel wheel assuming that would clear my front brakes.

Question:
Would a 8 ¾” B-Body rear that is 3” wider overall push the rear wheels back out into the quarter panel enough so I can safely run the same positive BackSpace wheels front and rear? What BackSpace am I looking for (5.5” I’m guessing)?

Help!


1971 6.1 Gen III Hemi Duster
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Brian] #1714027
12/22/14 03:29 PM
12/22/14 03:29 PM
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Look at the articles in the tech archives on Tim's red Valiant. We sat his car up to use Mustang 17x8 (or 17x9) rims on four corners. It had a B-body rear end under it and special hubs up front.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: AndyF] #1714028
12/22/14 04:02 PM
12/22/14 04:02 PM
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Houston Tx
Uhcoog1 Offline
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Brian-

Yes, you *should* be able to run the same wheels square on the car with a 68-70 B body rear. You may need slightly more width.

The front ride height also has a significant impact on the best backspacing in the front.

When doing your math, keep in mind the A body swapped to a 5x4.5" is slightly wider than the 5x4" original.

I've got a spare gt500 wheel (18x9.5, +45mm offset = 7.2" backspacing) and an old continental scrub you can mount. You can play with it and spacers to find your ideal tire position in the front wheel well and then set up the rear axle to fit the same wheel. Come borrow it whenever you like.


-'02 Dodge Viper Ex-World Challenge racecar
-'73 Duster, 6.1 based 392 hilborn hemi, tko600, full floater rear 9", Hellwig custom bars, viper brakes, built for road course
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Uhcoog1] #1714029
12/22/14 10:18 PM
12/22/14 10:18 PM
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Saint Peters, MO
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Brian Offline OP
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Wade,

Trade you the wheel and tire for a 5.7 bare block and an engine stand!

Here is what I'm now considering:

17"x 8", 25mm backspacing (5.5") I hate to go to an aftermarket wheel, but these look good to me and are cost effective.

http://www.customwheelsexpress.com/custo...VGRsaAnGl8P8HAQ

Looking at these tires:

Potenza S-04 Pole Position $128 at the Tirerack.


1971 6.1 Gen III Hemi Duster
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Brian] #1714030
12/22/14 10:23 PM
12/22/14 10:23 PM
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houston texas
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I had the tire measuremet tool also.
Bolts to the hub and allows you to determine if what you want will fit.
Percy's made it.


U Ian borrow it too


if You Like Gremlinsteve. Gremlinsteve Likes You.
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: gremlinsteve] #1714031
12/23/14 02:07 AM
12/23/14 02:07 AM
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Granite Bay CA
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Those wheel jigs are pretty cool but for me, nothing compares to having an actual tire and wheel bolted in place. I like having the ability to actually see right in front of me where I can add or subtract the wheel offset.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: AndyF] #1714032
12/23/14 03:05 AM
12/23/14 03:05 AM
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Posts: 27,468
So Cal
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Quote:

Look at the articles in the tech archives on Tim's red Valiant. We sat his car up to use Mustang 17x8 (or 17x9) rims on four corners. It had a B-body rear end under it and special hubs up front.




Did you use a 65-67 B-body rear or 68-70 B-body rear?

People should realize carefully picking between those two are different widths and can help fitment with whatever your particular rims' backspacing.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Brian] #1714033
12/23/14 03:35 AM
12/23/14 03:35 AM
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So Cal
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Quote:

Here’s the deal, I want to go to a 17” x 8” wheel probably running a 235/50-17 which are 26.3” tall all around on my 1971 Duster. This size tire allows me to run modern maximum performance summer tires while still retaining enough sidewall height to look correct. Ideally I would like to run the same size wheel with the same offset (BackSpace) all around as well. I may consider larger rear tires for the track if traction is a big problem.

Since I’m also upgrading the front suspension to 73-76 spindles with 11 ¾” discs with Gen I Viper calipers that will push the front wheels out requiring a wheel with a lot of positive BackSpace; it seems that the narrow A-Body 8 ¾” rear is not wide enough and will require a much deeper negative BackSpace to push the wheels back out into the quarter Panels. If that’s the case, I can’t rotate the tires front to rear and would have to carry a generic spare tire like a 205/70-15 on a steel wheel assuming that would clear my front brakes.

Question:
Would a 8 ¾” B-Body rear that is 3” wider overall push the rear wheels back out into the quarter panel enough so I can safely run the same positive BackSpace wheels front and rear? What BackSpace am I looking for (5.5” I’m guessing)?

Help!




The 68-70 B-body rear that is 3" overall wider will be 1.5" wider on each side. That's compared to a original A-body rear with thinner 5x4 axle flanges.

I run thin axle flanges on a re-drilled original 5x4 axles. I have found 4.5 backspacing was max with a 245 wide 50 series tire on an 8" rim. More than that, the tire will rub the leaf. Much less than that the tire my rub or will be unnecessarily closer to the outer fender lip. And that will keep you from the possibility of running a 255 or 265 wider tire on an 8" rim.

So if you run 5.5" backspace rear tires, you need a rear that sticks out on each side only 1" more than an original A-body rear. Or 2" more total drum to drum width.

To me, that would be a 65-67 B-body rear that is 59 1/2" drum to drum. That's 2 1/8" wider or 1 1/16" on each side wider.

Also, do you plan to run rear disks? Typical rear disk have a thicker flange plate than a drum. Would be nice to know that difference now and account for it.

Last edited by autoxcuda; 12/23/14 03:52 AM.
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: autoxcuda] #1714034
12/23/14 03:49 AM
12/23/14 03:49 AM
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Saint Peters, MO
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Brian Offline OP
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Quote:

The 68-70 B-body rear that is 3" overall wider will be 1.5" wider on each side. That's compared to a original A-body rear with thinner 5x4 axle flanges.

I run thin axle flanges on a re-drilled original 5x4 axles. I have found 4.5 backspacing was max with a 245 wide 50 series tire on an 8" rim. More than that, the tire will rub the leaf. Much less than that the tire will run the outer fender lip and will keep you from running a 255 or 265 wider tire on an 8" rim.

So if you run 5.5" backspace rear tires, you need a rear that sticks out on each side only 1" more than an original A-body rear. Or 2" more total drum to drum width.

To me, that would be a 65-67 B-body rear that is 59 1/2" drum to drum. That's 2 1/8" wider or 1 1/16" on each side wider.

Also, do you plan to run rear disks? Typical rear disk have a thicker flange plate than a drum. Would be nice to know that difference now and account for it.



I plan on running Discs all around.


1971 6.1 Gen III Hemi Duster
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Brian] #1714035
12/23/14 04:04 AM
12/23/14 04:04 AM
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Posts: 27,468
So Cal
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Quote:

Quote:

The 68-70 B-body rear that is 3" overall wider will be 1.5" wider on each side. That's compared to a original A-body rear with thinner 5x4 axle flanges.

I run thin axle flanges on a re-drilled original 5x4 axles. I have found 4.5 backspacing was max with a 245 wide 50 series tire on an 8" rim. More than that, the tire will rub the leaf. Much less than that the tire will run the outer fender lip and will keep you from running a 255 or 265 wider tire on an 8" rim.

So if you run 5.5" backspace rear tires, you need a rear that sticks out on each side only 1" more than an original A-body rear. Or 2" more total drum to drum width.

To me, that would be a 65-67 B-body rear that is 59 1/2" drum to drum. That's 2 1/8" wider or 1 1/16" on each side wider.

Also, do you plan to run rear disks? Typical rear disk have a thicker flange plate than a drum. Would be nice to know that difference now and account for it.



I plan on running Discs all around.




Do you know the thickness of the rear disk at the axle flange portion?

Just went in garage and measured a stock A-body drum at around 0.110"

Last edited by autoxcuda; 12/23/14 04:05 AM.
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: autoxcuda] #1714036
12/23/14 04:04 PM
12/23/14 04:04 PM
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Article says it was a '67 B-body rearend. I don't remember anymore myself so I'll go with what the article says.

http://www.hotrod.com/how-to/chassis-suspension/mopp-1204-1968-plymouth-valiant-track-day-prep/

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: AndyF] #1714037
12/23/14 04:50 PM
12/23/14 04:50 PM
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Quote:

Article says it was a '67 B-body rearend. I don't remember anymore myself so I'll go with what the article says.

http://www.hotrod.com/how-to/chassis-suspension/mopp-1204-1968-plymouth-valiant-track-day-prep/




65-67 rear end rings a bell to me from what Tim has posted over the years. That's why I asked.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: autoxcuda] #1714038
12/25/14 10:29 AM
12/25/14 10:29 AM
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I had an 8 3/4 in my duster with the 5.7" bs mustang rims. I didn't pull it out of the car but I was told it came from a 70 coronet. the width worked out good.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: JAMESDART] #1714039
12/25/14 04:09 PM
12/25/14 04:09 PM
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hawaii
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I agree with above replies, my '69 rear end needs 6.25" bs wheels (8.75" width) to fit on a Valiant. With the added room in the wheel wells on Dusters, I'd think a 5.5" bs would be about perfect using the earlier rear end and 8" wheels.

Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: pauly v.100] #1714040
12/26/14 12:46 AM
12/26/14 12:46 AM
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Saint Peters, MO
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Brian Offline OP
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I'm waiting to hear about '67 B-Body 8 3/4", sounds like it would be perfect, thanks!


1971 6.1 Gen III Hemi Duster
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: gremlinsteve] #1714041
12/26/14 01:26 AM
12/26/14 01:26 AM
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Saint Peters, MO
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Brian Offline OP
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Quote:

I had the tire measurement tool also.
Bolts to the hub and allows you to determine if what you want will fit.
Percy's made it.

U can borrow it too



Steve, I'm going to take you up on that offer once I get the car back in the garage with the motor and transmission, leaf springs and 8 3/4" installed. The way this project is moving forward, probably around March! Thanks for the offer!

Brian


1971 6.1 Gen III Hemi Duster
Re: BackSpace question with a B-Body 8 ¾” in an A-Body [Re: Brian] #1714042
12/26/14 01:28 AM
12/26/14 01:28 AM
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Nebraska
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I have a 67 B body rear. The track is still narrower than the front but with disc's in the rear it would be about right or close. I think my rear wheels are about 1/2" deeper than the fronts outer lips.


Mopar to the bone!!!






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