Disc brake swap Track width

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Losi

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Getting ready to order all of doctor diffs stuff to convert the front and rear to disc.. and larger bolt pattern. (front cobra stage 3, rear just the basic kit)
by swapping to the spindles they sell plus doing that swap i am told that my track width will increase a lot roughly 1/2.
I would like to run a 17" Wheel whether its both 8" or a front 7". What would be my easiest option to locking down a correct backspace/offset of wheel before i pull the trigger on all of this...

Is there any other swaps that help retain stock track width front and rear to help with wheel selection??? the rear is a a body 8 3/4 67 Notchback cuda
 
Really covered this in your other thread. The 73+ Mopar disk spindles add most of that width. There used to be a Wilwood kit that maintained a narrower track width, but it’s no longer available.

This is the factory track width change, using factory spindles. Any kit that uses 73+ disk spindles will have this much additional width, at minimum

IMG_5546.jpeg


The stage 3 DoctorDiff kit adds an additional 5/16” per side to this if my memory serves.

As far as what you can do, it’s pretty simple. If you want 7” wide rims, you should run at least 4.25” of backspace. With that you should be able to safely run up to about a 225mm wide tire up to about 25.7” tall on your Barracuda. With a 17” rim you can run up to about 5.6” of backspace before you hit the outer tie rod end.

With an 8” front rim you should probably run at least 5” of backspace, which requires a 17” or larger rim. Less backspace than that and your tire width will be limited to what you could run on a 7” wide rim. Between about 5.25” and 5.6” of backspace will let you run a 245 up front, potentially even a 255 close to the 5.6” backspace number. Alternatively, with an 18” rim you can go up to ~6.3” of backspace, which allows a 275 up front on a 9” wide rim. Same rules for an 18x8 as a 17x8, just with the option for more than 5.6” of backspace.
 
72bluNblu said:
Really covered this in your other thread. The 73+ Mopar disk spindles add most of that width. There used to be a Wilwood kit that maintained a narrower track width, but it’s no longer available.

This is the factory track width change, using factory spindles. Any kit that uses 73+ disk spindles will have this much additional width, at minimum

View attachment 1716170741

The stage 3 DoctorDiff kit adds an additional 5/16” per side to this if my memory serves.

As far as what you can do, it’s pretty simple. If you want 7” wide rims, you should run at least 4.25” of backspace. With that you should be able to safely run up to about a 225mm wide tire up to about 25.7” tall on your Barracuda. With a 17” rim you can run up to about 5.6” of backspace before you hit the outer tie rod end.

With an 8” front rim you should probably run at least 5” of backspace, which requires a 17” or larger rim. Less backspace than that and your tire width will be limited to what you could run on a 7” wide rim. Between about 5.25” and 5.6” of backspace will let you run a 245 up front, potentially even a 255 close to the 5.6” backspace number. Alternatively, with an 18” rim you can go up to ~6.3” of backspace, which allows a 275 up front on a 9” wide rim. Same rules for an 18x8 as a 17x8, just with the option for more than 5.6” of backspace.
Click to expand...
From what I can tell interpreting what you wrote these wheels that I posted above should fit the criteria? Or no
 
Losi said:
From what I can tell interpreting what you wrote these wheels that I posted above should fit the criteria? Or no
Click to expand...

In the front they'd probably work. The ~5.6" backspace where the outer tie rod end clearance starts to be an issue is with just the '73+ spindles, so with the 13" DoctorDiff kit adding 5/16" you'd be right there.

But in the back they'd have way too much backspacing. As I mentioned in your other thread your first choice of 17x8's was actually about right for rear backspacing. That's the problem with A-bodies, as illustrated with the picture of the track widths. The front and rear don't use the same backspace when you start looking at running wider tires. In the back with an A-body 8 3/4, BBP axles, and disk brakes with the stock spring locations you'd be looking for a backspace around 5" to 5.25". You can use less (like the 17x8's with 4.5" you posted in your other thread) if you don't go for the widest possible tire. But with the 8 3/4, BBP axles and disks you'll probably have about 6.25" or so from wheel mounting surface back to the leaf spring. About a 1/2" needs to be clearance, and around a 1/2" will be tire overhanging the rim (on most tires you'd mount on a 17x8" rim), so that's 5.25" for your backspace. Again, if you limit the width you can run less, but you're not going to be able to run 5.9" of backspace with any tire that will fit on that rim.
 
72bluNblu said:
In the front they'd probably work. The ~5.6" backspace where the outer tie rod end clearance starts to be an issue is with just the '73+ spindles, so with the 13" DoctorDiff kit adding 5/16" you'd be right there.

But in the back they'd have way too much backspacing. As I mentioned in your other thread your first choice of 17x8's was actually about right for rear backspacing. That's the problem with A-bodies, as illustrated with the picture of the track widths. The front and rear don't use the same backspace when you start looking at running wider tires. In the back with an A-body 8 3/4, BBP axles, and disk brakes with the stock spring locations you'd be looking for a backspace around 5" to 5.25". You can use less (like the 17x8's with 4.5" you posted in your other thread) if you don't go for the widest possible tire. But with the 8 3/4, BBP axles and disks you'll probably have about 6.25" or so from wheel mounting surface back to the leaf spring. About a 1/2" needs to be clearance, and around a 1/2" will be tire overhanging the rim (on most tires you'd mount on a 17x8" rim), so that's 5.25" for your backspace. Again, if you limit the width you can run less, but you're not going to be able to run 5.9" of backspace with any tire that will fit on that rim.
Click to expand...
lmao i am exhausted searching the web for a 17x8 wheel that will work for front and rear that i am ok with looks wise... i think i finally found something that satisfies both lol. im hoping the .04 extra backspace wont be critical lol
1701227064322.png


1701227111488.png
 
72bluNblu said:
Yep, that should work!
Click to expand...
so now onto tires... with this wheel setup im assuming for front 245/45/17 and for rear the same or can i go wider? or taller to a 50? more the more muscle car stance or so.. if my tire sizes do not match i am not to worried about the rotation benefit. what tires do you like? my other cars i have ran firehawk indys
 
Losi said:
so now onto tires... with this wheel setup im assuming for front 245/45/17 and for rear the same or can i go wider? or taller to a 50? more the more muscle car stance or so.. if my tire sizes do not match i am not to worried about the rotation benefit. what tires do you like? my other cars i have ran firehawk indys
Click to expand...

You should be able to do a 245/45/17 up front. In the back you have more room, you could run a 245/50/17 if you wanted or even a 255/45/17 or 255/50/17, although you may only find light truck tires in the larger 50 series tires so you’ll have to see what’s available to match the front.

I haven’t run the Fire Hawk Indy’s myself but I’ve heard good things about them. Beyond that it depends on your plans for the car, I try to keep the tread wear ratings in the 200’s nowadays but definitely below about 350.
 
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