Wheels for a duster offset and backspace

[BOXHEADgumby]

Thanks so much! I get it now and am certain that I’ll end up running a spacer if I want to avoid full custom wheels which I don’t mind spacers if I can find a set that bolt to the car in place of longer studs. Next hurtle in the decision process would be the center bore as I would rather run a hub centric wheel.

I also found this little guy, Wheel Offset to Backspace Calculator | GTSparkplugs

 

[famous bob]

Just lay a steel ruler across the face of the hub where the back of wheel mounts. Then measure the distance from the ruler to your leaf spring. Deduct 1", and that is your max back space. My Dart measures 5.5" there, deduct 1", I get 4.5" max backspace. The tire will take up 1/2", then 1/2 " clearance to the leaf. That's how I understand back space.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This totally depends on section width of the tire !

 

[roccodart440]

Blu is always down to help and fights the good fight with small wheelers haha

I end up with 18x8.5 5.1 bs with a 225/45 in the front and 18x9.5 5.3 bs 255/40 in the rear.

Im planning some new tires for the summer, I’ve got room for a 245 in front and 275 in rear.

View attachment 1715286781

Those wheels are soooo nice

 

[QMopar]

Easiest way to determine the backspace is shown in the video I posted above, pull the wheels and measure from the outside of the lip on the wheel on the backside to the mounting surface. The rims may also be stamped or marked on the inside, but that will probably be an offset number.

The problem is that with an A-body the backspacing needed in the front and in the back isn’t the same. The wider the tire you’d like to use, the more that’s true. So, to use the same rims front and rear limits your width.

The other issue is the rear axles aren’t all the same width. A-body 8 3/4’s are wider than A-body 7.25 and 8.25 rear axles. So, what rear axle do you have?

I’m also assuming you have the 5x4.5” bolt pattern since you have 18’s already.

• Ok, thank you. That makes sense on how to measure offset. I took some pics last year when I checked the brakes (attached) but I'll have to take them off at some point and measure to be sure. It's in storage now.
• I like the idea of having the wheels/tires all the same but it's not a deal breaker. Just thought it would look a little better and again, can rotate to prolong tire life. Maybe that's not something I need to be that concerned about.
  
• I have a 7.25 in it now but plan to swap to an 8.25 - with the idea of going to Jeep ZJ rear disc brake swap.
  
• Yes, 5x4.5"

 

[BOXHEADgumby]

Got the wheels all mounted! Figured I’d share some photos, thanks for all the help, yes I ended up going with hubcentric spacers for the rear so that I could get the same rim all around without forking out 500 or more per wheels for customs.

 

[MRGTX]

Got the wheels all mounted! Figured I’d share some photos, thanks for all the help, yes I ended up going with hubcentric spacers for the rear so that I could get the same rim all around without forking out 500 or more per wheels for customs.

View attachment 1715312404

View attachment 1715312405

I like the style a lot!! Black wheels with the black stripes...very nice! Great looking car, man.

I'm wondering if you could run some spacers on the back to push them outboard a bit...I realize that the narrower rear track is a standard A-Body thing and it probably wouldn't help handling....but I think you have the room.

EDIT: just saw above that you'll be swapping in an 8.25" rear. That will move your wheels out a little anyway.

 

[72bluNblu]

I like the style a lot!! Black wheels with the black stripes...very nice! Great looking car, man.

I'm wondering if you could run some spacers on the back to push them outboard a bit...I realize that the narrower rear track is a standard A-Body thing and it probably wouldn't help handling....but I think you have the room.

EDIT: just saw above that you'll be swapping in an 8.25" rear. That will move your wheels out a little anyway.

Swapping to an 8.25" won't move the wheels. The BBP 7.25 and 8.25" rear axles are the same width. Adding the disks in the back will widen the track width a little though, usually 3/16" to 1/4".

 

[famous bob]

Swapping to an 8.25" won't move the wheels. The BBP 7.25 and 8.25" rear axles are the same width. Adding the disks in the back will widen the track width a little though, usually 3/16" to 1/4".

I have read these posts, even figured my offset for grins from the chart. But still cant see why a person would care about offset, if you got the backspaceing right and the wheels/tires fit !! Who gives a flip ?

 

[72bluNblu]

I have read these posts, even figured my offset for grins from the chart. But still cant see why a person would care about offset, if you got the backspaceing right and the wheels/tires fit !! Who gives a flip ?

Offset is just a different way to measure the rim specs. If you have a backspace measurement, you have an offset measurement too. Backspace is measured from the lip of the rim to the mounting surface and is usually listed in inches. Offset is measured from the centerline of the rim to the mounting surface and is listed in mm. Both are just easy to use.

Offset is easier to use if you’re changing or comparing different rim widths. Offset tells you the centerline of the wheel. If you have your wheels centered in the wheel well, and want to use a wider or narrower rim, you just keep the offset the same. If you keep the backspace the same but change the width of the rim you’re actually moving the rim in or out depending on the change in width.

 

[famous bob]

Offset is just a different way to measure the rim specs. If you have a backspace measurement, you have an offset measurement too. Backspace is measured from the lip of the rim to the mounting surface and is usually listed in inches. Offset is measured from the centerline of the rim to the mounting surface and is listed in mm. Both are just easy to use.

Offset is easier to use if you’re changing or comparing different rim widths. Offset tells you the centerline of the wheel. If you have your wheels centered in the wheel well, and want to use a wider or narrower rim, you just keep the offset the same. If you keep the backspace the same but change the width of the rim you’re actually moving the rim in or out depending on the change in width.

Agree w/ all this, ^^^^^^^^^^^^^^^ been doing it for 50 plus, never worried about offset tho-???

 

[Clelan]

Got the wheels all mounted! Figured I’d share some photos, thanks for all the help, yes I ended up going with hubcentric spacers for the rear so that I could get the same rim all around without forking out 500 or more per wheels for customs.

View attachment 1715312404

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Can you share the details on what you bought? Wheel brand and specs, tire brand and specs? Or did I miss it?

Cley

 

[72bluNblu]

Agree w/ all this, ^^^^^^^^^^^^^^^ been doing it for 50 plus, never worried about offset tho-???

Every wheel you’ve ever bought had an offset spec. Just because you didn’t know it doesn’t change that, and just because you didn’t use it doesn’t mean it wouldn’t have been helpful.

 

[famous bob]

Every wheel you’ve ever bought had an offset spec. Just because you didn’t know it doesn’t change that, and just because you didn’t use it doesn’t mean it wouldn’t have been helpful.

Don't think it would have helped me , never needed to know, or maybe , didn`t care ? . ????????

 

[BOXHEADgumby]

Can you share the details on what you bought? Wheel brand and specs, tire brand and specs? Or did I miss it?

Cley

I got the motegi tracklites. 17x8 rear 17x7 front
running nitto tires 225/45/17 front and 245/45/17 rear. The backspacing was 5.5 if I remember right so I used a 1.5 spacer to bring the rear out to what I needed it to be. The front I needed up having to run a small spacer to make the wheels fit because the advertised centerbore was the correct size however the lip that is machined to bolt the centercap on was not accounted for in advertising. I went back and forth about just grinding the lip off and figuring out the center cap later or the route I took. All and all I would say if we had the ability to “upgrade to a more modern smaller hub I think wheel choices could open up even more.

 

[72bluNblu]

I got the motegi tracklites. 17x8 rear 17x7 front
running nitto tires 225/45/17 front and 245/45/17 rear. The backspacing was 5.5 if I remember right so I used a 1.5 spacer to bring the rear out to what I needed it to be. The front I needed up having to run a small spacer to make the wheels fit because the advertised centerbore was the correct size however the lip that is machined to bolt the centercap on was not accounted for in advertising. I went back and forth about just grinding the lip off and figuring out the center cap later or the route I took. All and all I would say if we had the ability to “upgrade to a more modern smaller hub I think wheel choices could open up even more.

Yeah the center bore issue comes up a lot. It really depends on the design of the rim, some are very thick at the hub so having a wheel cap smaller than the center bore isn't a problem. On others, as you found, the center bore narrowing down to a smaller wheel cap can be an issue. I had that problem with my Enkei RPF1's, even with the smaller diameter aluminum hubs that I have with the 13" DoctorDiff brakes I run. I just took the wheels to my machine shop and had them bored all the way through at 73.1 mm, then did a little custom work on the cap.

 

[Dodge73Dart]

Just lay a steel ruler across the face of the hub where the back of wheel mounts. Then measure the distance from the ruler to your leaf spring. Deduct 1", and that is your max back space. My Dart measures 5.5" there, deduct 1", I get 4.5" max backspace. The tire will take up 1/2", then 1/2 " clearance to the leaf. That's how I understand back space.

I also have a Dart 1973 Sport. I used to have a Crager 14x7 or 8 in a chrome reverse.
I would love to find that same wheel setup but unsure of the specs that would work.
The car is stock and will have Air shocks on rear.
You pretty much answered some of my question with the 4.5” backspace. So I go with a 4.5 back space and what would be my maximum with using a chrome reverse wheel? I also remember that I ran G 60 14 tires on rear.
thanks to all.

 

[69_340_GTS]

The reason "offset" matters is because many wheel manufacturers use it to dimension their wheels. They don't refer to "backspace" in their specs. So you need to know what it means, and how to convert it to more meaningful numbers.

 

[72demon96]

Blu is always down to help and fights the good fight with small wheelers haha

I end up with 18x8.5 5.1 bs with a 225/45 in the front and 18x9.5 5.3 bs 255/40 in the rear.

Im planning some new tires for the summer, I’ve got room for a 245 in front and 275 in rear.

View attachment 1715286781

What kind of rims are those?

 

[72bluNblu]

I also have a Dart 1973 Sport. I used to have a Crager 14x7 or 8 in a chrome reverse.
I would love to find that same wheel setup but unsure of the specs that would work.
The car is stock and will have Air shocks on rear.
You pretty much answered some of my question with the 4.5” backspace. So I go with a 4.5 back space and what would be my maximum with using a chrome reverse wheel? I also remember that I ran G 60 14 tires on rear.
thanks to all.

First, air shocks are a disaster. They're an excellent way to tear the shock mounts right out of the car, because the shock mounts were never intended to carry the weight of the car. If you run the pressure up on your air shocks to raise the back of the car, you take weight off the springs and move it to the shocks. Now your shock mounts are carrying the weight of the car instead of the springs. If you want to run the back of the car way up in the air, get different springs with a higher arch.

Second, all A-body rear axles are not the same width. An 8" wide rim with a 4.5" backspace works well on a Duster with an A-body 8 3/4 and BBP axles. But A-body 7.25/8.25 axles are narrower than an A-body 8 3/4 with BBP axles, so more than likely you will not want 4.5" backspace on an 8" rim. More like 4.25" or even 4" if you're going to run 275's back there. With the back end of the car way up in the air the clearance to the quarters will be less of an issue anyway.

If want to max out the tire that will fit INSIDE the wheel well, a 15x8 with a 275/60/15 will be about it with the springs in the stock location and no trimming on the quarter lip. Ideal backspace will depend on what rear axle you have. If you're going to run '70's street freak style with the back end up in the air like a 4x4, then you can run 15x10's and whatever you want, because the tires hanging outside of the quarters won't be a concern with the quarter lip 3' off the ground.

 

[Dodge73Dart]

First, air shocks are a disaster. They're an excellent way to tear the shock mounts right out of the car, because the shock mounts were never intended to carry the weight of the car. If you run the pressure up on your air shocks to raise the back of the car, you take weight off the springs and move it to the shocks. Now your shock mounts are carrying the weight of the car instead of the springs. If you want to run the back of the car way up in the air, get different springs with a higher arch.

Second, all A-body rear axles are not the same width. An 8" wide rim with a 4.5" backspace works well on a Duster with an A-body 8 3/4 and BBP axles. But A-body 7.25/8.25 axles are narrower than an A-body 8 3/4 with BBP axles, so more than likely you will not want 4.5" backspace on an 8" rim. More like 4.25" or even 4" if you're going to run 275's back there. With the back end of the car way up in the air the clearance to the quarters will be less of an issue anyway.

If want to max out the tire that will fit INSIDE the wheel well, a 15x8 with a 275/60/15 will be about it with the springs in the stock location and no trimming on the quarter lip. Ideal backspace will depend on what rear axle you have. If you're going to run '70's street freak style with the back end up in the air like a 4x4, then you can run 15x10's and whatever you want, because the tires hanging outside of the quarters won't be a concern with the quarter lip 3' off the ground.

Thanks for the info
As for the shock mounts that issue was already addressed during the restoration. I am running a stock 7.25 rear.
As mentioned in the initial post I used to run 14x7 chrome reverse. I never raised the rear real high and had to shocks to compensate for music equipment at times.
So I’m looking for what might work for. 14” wheel. thanks

 

[72bluNblu]

Thanks for the info
As for the shock mounts that issue was already addressed during the restoration. I am running a stock 7.25 rear.
As mentioned in the initial post I used to run 14x7 chrome reverse. I never raised the rear real high and had to shocks to compensate for music equipment at times.
So I’m looking for what might work for. 14” wheel. thanks

If you stay with a 14” rim the largest street tire currently available is a 245/60/14, BFG T/A. On a Duster that tire will still look pretty small, and it will work fine on a 14x7. A backspace of 4” would be fine, but with a 245 anything from 4.25” all the way down to 3.5” would work and the smaller numbers would likely look better because the wheels won’t be hiding all the way back in the wheel wells. 14” wheels severely limit your tire choices, both in size and brand.

A 15x8 with about 4.25” of backspace would be the way to go, with a 275/60/15 on the back. That will give you “the look” you’re likely after with your car set up the way it is. No one makes a 275 for a 14” rim anymore.

 

[roccodart440]

Hoosier Tire makes a Quick Time DOT Tire (bias full tread) 275/55-14

Coker Tire makes a Silvertown Radial 265/50R14

 

[72bluNblu]

Hoosier Tire makes a Quick Time DOT Tire (bias full tread) 275/55-14

Coker Tire makes a Silvertown Radial 265/50R14

Ok, you got me there. But a bias ply and a Coker that costs what now?

For frequent street use I wouldn’t want to tie myself to either of those options. Even just on availability it probably wouldn’t be great. I guess if you buy one set of tires every 10 years it might not be a big deal.

 

[roccodart440]

You'd never see me with anything less than a 15 either.

 

[diymirage]

You'd never see me with anything less than a 15 either.

And you'd never see me with anything more


(On a muscle car, of course)