BackSpace question with a B-Body 8 ¾” in an A-Body Duster

[JBrian]

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!

 

[zinser72]

I have a b body 8 3/4 rear under my 72 duster and i run 18x7 wheels with 5.5" backspace. They have the perfect amount of quarter clearance if you ask me, about 1/2" on the outside and about 3/4" to the stock location leafs with 235/45 tires. Hope this helps!

 

[pauly v.100]

18x8.75 with 6.25 bs on an 8.75 rear on mine.

you should be able to run squared with 5.75-6.0 bs. remember the duster wells are a bid wider towards the outside so there should be plenty of room, and theres enough bs to get away from using a spacer in front.
the mustang wheels that so many people use are 17x8 w/ 5.72 backspace and fit perfect with a b-body rear.

 

[72bluNblu]

That's an awfully skinny tire. You can get 255/45/17's on a 17x8 too, that would be a 26" tall tire as well. Also, going taller than 26" can cause fender front corner interference issues, even on Dusters. 255's will fit on all 4 corners.

I have 275/35/18's on 18x9's up front on my duster, +35mm offset but I run dr diff's 13" brake kit and 3mm spacers to keep them off the frame. In the back I have a 68-70 B body rear with a 1/2" spring offset and 18x10's with 295/35/18's. They've got a 38mm offset, which is a 7" backspace.

 

[JBrian]

That's an awfully skinny tire. You can get 255/45/17's on a 17x8 too, that would be a 26" tall tire as well. Also, going taller than 26" can cause fender front corner interference issues, even on Dusters. 255's will fit on all 4 corners.

Just back from the shop scrubbing some lines on the leading edge of the front fender. 1.5" tapering in a smooth arch most of the way up the fender. We'll also roll the entire top lip of both the front fenders and rear quarters. The goal is to make it look factory, a difficult task!

As far as the tires, I'm trying to stay away from steam rollers and do my best to hind the tires. I am trying my best to have an all stock look while building a competent handling Duster. It already kills me to most likely have to go with an after market wheel:

http://www.customwheelsexpress.com/...h7LSl0nLxJ6SuKf7xAyAfAd8DA247EVGRsaAnGl8P8HAQ

to run these tires in a 235/5017: Potenza S-04 Pole Position

 

[72bluNblu]

Yeah it's too bad that the 17" rally's and magnum wheels that year one sells don't come with enough backspace to run on the front of the A-bodies...

The 235/50/17's are pretty easy to find because it's a stock Mustang size for the newer cars. 245's are hard to find in the right height, which puts the 255's as the next best option. I really don't think the 255's qualify for "steamroller" status, but obviously you can get a pretty decent handling set up with the 235's, the new mustangs handle pretty well with them.

 

[JBrian]

Yeah it's too bad that the 17" rally's and magnum wheels that year one sells don't come with enough backspace to run on the front of the A-bodies....

I asked Year-One customer service if they were considering offering the 17" rally in "Other" positive offsets. I received an abrupt "No" seeming like a lot of people have asked the same question. They really messed up a great looking wheel by not offering them in the correct offset. I would say a mistake was made and they kept the stock offset of a 15" rally without taking into consideration the additional width. Instead of correcting the problem, they seems to get mad when the question keeps coming up! Nice customer service Year-One...

 

[72bluNblu]

I asked Year-One customer service if they were considering offering the 17" rally in "Other" positive offsets. I received an abrupt "No" seeming like a lot of people have asked the same question. They really messed up a great looking wheel by not offering them in the correct offset. I would say a mistake was made and they kept the stock offset of a 15" rally without taking into consideration the additional width. Instead of correcting the problem, they seems to get mad when the question keeps coming up! Nice customer service Year-One...

Can't say anything about YearOne's customer service, I try to avoid that place like the plague simply because of their prices.

As far as the offset on the 17" rallye's and magnum's goes, I don't think it was a mistake. Keep in mind that not all of the Mopar body styles use the same offset. The offset that those rims come in fits the E/B bodies perfectly in both 17x8 or 17x9. I have 17x9's on my Challenger with a 5" backspace and 275/40/17's on all 4 corners. Not from YO, but they're the same size.

In fact, the A bodies are pretty much the only ones that need a higher offset for those sizes, and even then that's only up front. And in the 17" diameter, 9" rims really don't work well up front on the A bodies because of tie rod interference issues. So that would mean just making a 17x8 with the higher offset. Although, if they did something smart and made a 17x8 with a 5.72" backspace they'd fit later mustangs too ( I know, I know). But more than likely the folks at Year One decided they wouldn't sell enough rims in that size to make it worthwhile.

 

[zac_F71]

I too am doing the uncut 68-70 b body 8 3/4 in my Demon but a 15" drag wheel instead, same MP offset hangers/shackles

drum to drum the 68-70 B body axle is 3" wider (1.5" a side) and I plan to look at wheels in the 4.5"- 5.5" back space range.. going to run a 275/60-15 drag radial

 

[72bluNblu]

I too am doing the uncut 68-70 b body 8 3/4 in my Demon but a 15" drag wheel instead, same MP offset hangers/shackles

drum to drum the 68-70 B body axle is 3" wider (1.5" a side) and I plan to look at wheels in the 4.5"- 5.5" back space range.. going to run a 275/60-15 drag radial

What width rim?

On a 10" wide rim with the 1/2" spring offset and a 68-70 B rear you'd want closer to 7" of backspace, that's what I'm running with 295's. With 275's you don't need that wide of a rim, but you'd still want more backspace than that.

For a 9" wide rim you'd want closer to 6.5" of backspace (no less than 6"), and for an 8" rim that would be 6" of backspace (no less than 5.5"). The minimum numbers I listed would put the outside of the tire in the same place as my 295's, but I trimmed my inner quarter lips back almost a 1/2", so I would try to go with the extra backspace. You'll still have more room than me to the springs because of the narrower tires.

 

[zac_F71]

8" wide wheel is the plan but if I can't find the back space I need I will go up to a 9"

I was planning in all honesty running a 15x8 w/ 5.5"BS Weld Prostar straight off my fox mustang- some one local to be said I need 4"- 4.5" or so though so I got a confused LOL

Sorry to thread jack..

 

[72bluNblu]

8" wide wheel is the plan but if I can't find the back space I need I will go up to a 9"

I was planning in all honesty running a 15x8 w/ 5.5"BS Weld Prostar straight off my fox mustang- some one local to be said I need 4"- 4.5" or so though so I got a confused LOL

Sorry to thread jack..

That 15x8 with 5.5" of backspace will be about the minimum you need to make it work. It'll probably depend on your car. If you have SS springs or similar higher arch springs you'll probably be ok, but if you sit low you might have to trim the quarter lip a little to keep from rubbing on the outside edge.

You' would need 4" to 4.5" of backspace with an A-body rear, not a B body.

 

[zac_F71]

That 15x8 with 5.5" of backspace will be about the minimum you need to make it work. It'll probably depend on your car. If you have SS springs or similar higher arch springs you'll probably be ok, but if you sit low you might have to trim the quarter lip a little to keep from rubbing on the outside edge.

You' would need 4" to 4.5" of backspace with an A-body rear, not a B body.

Ya I have SS 2800lb springs - I plan to roll the outer lip and will probably add 1" blocks to lower it some..