Latest tire 1970 Swinger with mopar off set shackles can I fit a 275 tire?

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70Roadkill

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I hate starting a new thread read about 15-20 pages and not clear so I have a 1970 Swinger with an 8 3/4 drum axle. I picked up a mopar off set shackles kit from a guy. I'd like to know can I tuck a 15x8 I'm guessing right now 4.5 backspace until I measure it in the wheel well with out jacking up the rear end? I'd rather not cut the wheel well but if I have to then I'd like to know will a 295 tire then fit and would a 15x10 with a 5" backspace fit or would it rub the springs? Thanks in advance.
 
On my 72 Swinger ... 15x8 4.5 backspace ... straight hangers and shackles ... 245x60x15 ... 1" clearance to the springs ... 3/4" to the rolled fender lip ... 1 1/2" to the bottom front of the fenderwell (the tight spot we seem to often forget) ... 275s are about 1 1/4" wider and 1" taller
 
275's will fit with the MP offset kit, you will not get 295's in there without a mini-tub and 3" relocation.

Do you have BBP or SBP drums? Makes a difference. With an offset kit to run 275's you'll want more like 5.5" of backspace. All you have to do is look at Unconventional's measurements, a 15x8 with 4.5" of backspace and a 245 only has 3/4" to a rolled fender lip. That means without rolling even a 245 would be pretty tight to the quarter, but there's still an inch to the springs where you only need about a 1/2". So, add a 1/2" to the backspace and now you're at 5", add another 1/2" for offset springs and now you're at 5.5" to center the wheel in the tub. And we still don't know if you've got BBP axles and brakes. If you do, you probably need even more backspace.

I think Peter's 18x9's have like 5.9" of backspace?
 
The only way you will know. Is if you get under there and measure.

Not only does many of our cars come with non-factory rear ends. Meaning it might be wider/narrower than a stock A body rear end. Even from the factory sometimes the rear end was not centered properly. Some guys have seen up to 1/4 difference in difference of clearance between the rear tires. This can affect what you can run.

The best thing to do. Is get under and measure your hard points. Measure from the wheel mounting surface to the farthest out hard point. Usually the fender lip. Then from the wheel mounting surface to the farthest in hard point. Usually the spring/shackles. These two numbers together will give you the total section width you can run. These numbers separately will tell you how much back space you need.

For example. Lets say from wheel mounting surface to fender lip is 4 inches. And from wheel mounting surface to springs is 6 inches. You can run up to a 9 inch tire. This will leave you a 1/2 extra clearance on each side. You WILL want this. The rear end does move side to side, especially in hard cornering. Some guys run as little as 1/4. But you will get occasional tire rubbing.

Now for back space. A 9 inch tire will probably want a 7-8 inch wide rim. Lets say 8 inches for ease of math. You want 3.5 inches of the TIRE beyond the mounting surface. And 5.5 inches behind it. That means you pick an 8 inch rim with 5 inches of backspace. This will give you 5.5 inches of tire behind the mounting surface. And 3.5 inches of tire beyond the mounting surface. This is just an example. Your setup will probably be crazy different.

Clear as mud? I know in your case it can be difficult to measure since you don't have the offset kit in. But you should be able to mark where it would be and figure it from there. As I said. There is no "one size" fits all with our cars. The biggest problem being how much people have touched them before we get them. Who knows if that rear end is wider, or shorter, than it should be. Or if the springs are in the right spot. Or if the rear end is actually centered (often it isn't). I just hate to see guys go out and buy a set of whatever tires/rims, go to put them on and no bueno. It's easier to get under there and measure.
 
With the growing popularity of "Pre-runner" trucks around here, 3" to 6" of tire hanging out of the fenders. I don't think local law enforcement will notice my next combo with the 9" and the radiused fenderwells.
 
72bluNblu said:
275's will fit with the MP offset kit, you will not get 295's in there without a mini-tub and 3" relocation.

Do you have BBP or SBP drums? Makes a difference. With an offset kit to run 275's you'll want more like 5.5" of backspace. All you have to do is look at Unconventional's measurements, a 15x8 with 4.5" of backspace and a 245 only has 3/4" to a rolled fender lip. That means without rolling even a 245 would be pretty tight to the quarter, but there's still an inch to the springs where you only need about a 1/2". So, add a 1/2" to the backspace and now you're at 5", add another 1/2" for offset springs and now you're at 5.5" to center the wheel in the tub. And we still don't know if you've got BBP axles and brakes. If you do, you probably need even more backspace.

I think Peter's 18x9's have like 5.9" of backspace?
Click to expand...

I'll be running a bbp axles most likely the dr. Diff ones with stock rear drums set up and a disc conversion up front. I will set the axle up put it all in there and see what gives. I'm hoping not to have to mini tub but if I do I will. Just more labor and time for me to do it.
 
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