What Wheel Backspacing for an F-Body 8.25 in an A-Body?

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HTMLmopars

HTMLmopars

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Trying to line things up for my planned 8.25 swap into my 68 Valiant. I have wheels that are 15x8, 4.5"bsp, bbp, and just mocked them up on the rear outside of the car, and it measured about 68" from the edge of the wheel to the edge of the wheel. I'm not feeling great about that width, especially with my planned 255/60/15 tires (I'm willing to do 235s, but I'm trying to get a taller tire to bring down highway rpm with a more aggressive rear end ratio). I can't find a wheel in my price range (cheap) with the bolt pattern and more backspacing than 4.5. So are the 255 tires just a dream and won't fit? and will the wheels I have now clear the fenders with any tire?
 
An F-body 8.25 is like 59.6" wide from wheel mount to wheel mount. That's about the same as a 65-67 B body 8 3/4 (the F body 8.25 is a little wider). There's no way in heck you'll fit 15x8's with a 4.5" backspace on there with 255's. I don't think you're going to fit those on there with any tire that would be recommended for an 8" wide rim.

Just roughly, that rear axle is about 1.75" wider than an A-body 8 3/4 with BBP axles and brakes. Which means you're going to need close to a 6" backspace on a 15x8 if you want to run 255's. And 255's may be pushing your luck anyway if you're planning on keeping the stock spring locations.

Before you buy rims, you're going to want to have that rear axle mounted in the car so you can measure the distances from the wheel mounting surface back to the springs, and from the wheel mounting surface out to the quarters. Those are the numbers you need to figure out what will fit your car. If you get an exact width on that rear axle, from where the wheels mount on each side, I can probably give you a better guess as to the kind of backspace you'll need. But it's going to be more than 4.5".
 
Does anyone have good places to get used wheels? My local Picknpull doesn't sell just wheels, they only sell full wheel/tire sets (all 4) and I only need two wheels, and don't really want any tires. Planning on checking out a few other local yards to see what they've got, but I expected the bbp wheels to be easier to find. Lengths on that axle will be coming as soon as I can convince a family member to help me hold a tape and straightedge in the rain.
 
BBP wheels are easier to find. Just not in a 15” rim. And on that note, you’re probably not going to find a used 15x8 with more than 4.5” of backspace.
 
72bluNblu said:
BBP wheels are easier to find. Just not in a 15” rim. And on that note, you’re probably not going to find a used 15x8 with more than 4.5” of backspace.
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A 7" rim should work, too. I'm looking for a 235 tire at least, which is what I'm running right now. I was thinking that the crown vic cop wheels looked like they had a bunch of backspacing, and they should be easy enough to find, and should be the right 5x4.5 bolt pattern
 
You have to go back past ‘97 for the Crown Vic cop wheels to be 15”, those were 15x7 with a 4.25” backspace. After that they went to 17”.

And 15x7 with a 4.25” backspace won’t work for you. That’s actually the same specs as the Mopar cop rims. I have a 68-70 B body 8 3/4 in my Duster. When I ran cop wheels on it I could only fit 225/60/15’s. Now, the 68-70 B rear is wider, but only by a 1/4” per side. The Duster quarters are a full inch wider than the quarters on your Valiant. So, still not going to work.

Any 15” with enough backspace to work with that F body rear axle is probably going to have to be custom.
 
72bluNblu said:
You have to go back past ‘97 for the Crown Vic cop wheels to be 15”, those were 15x7 with a 4.25” backspace. After that they went to 17”.
Click to expand...
Looking at 17s now. There are some reasonably priced new steelies that have over 4.5 offset on a 7" wide rim, so they might have a chance. Just looking at options at this point, going to put it all in the car and measure up everything before I get wheels.
 
I just measured 59.25" from WMS to WMS. Sounds like the ballpark that everyone has been saying I should be in. The axle is going out for spring perch narrowing tomorrow morning, so it should be basically ready to be put into the car as soon as tomorrow afternoon.
 
Took a while, and I forgot that I had this thread going, too, but got everything bolted up, and on the road. Wheels are 15x7, 4.5" bkspc and I fit 245/60 tires on them. I redid the springs with Durango parts, which gave me a lot more height out back, and I think without it, I would have a little interference, but nothing rolling the inner fenders couldn't fix
 
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