backspacing

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twayne24365

twayne24365

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so im thinking myself to death trying to get this figured out. i have 14x7 wheels with 4"bs and the tire i am running sits a little close to the fender side. i just upgraded to new dr diff axles with the large bolt pattern and am trying to find a set of steel wheels to use with 255/60 drag radials. in a perfect world i would use a 15x7 with 4.25-4.5 bs but the only wheels i can find like that are the police wheels.

that said, the only wheels i can find with those dimensions that are similar to the mopar wheel s have a +12mm offset, would that effect where the wheel and tire are located? or would i be ok with them?
 
Rallye wheels not a option?

What rim diameter and width are you looking at that has a +12 mm offset?
 
Look at specialtywheel.com, they have 15 x7 4 1/4 back spaced steelies.

Jeff
 
Car is a 72 swinger, I don't think 4 1/4 will bring the wheel in quite far enough to center it. And if the 15x7 with 12mm offset is 4.5bs that would very well work!
 
Well I quadruple checked and 4 1/4 bs will work.
So if a 15x7 with 4 1/4 will work, if I went to an 8" rim, what bs would I use then?
 
5.25; but will the sidewalls still clear the spring?
The 3/4 inch offset kit is cheap and easy to install.
Wheel Vintiques will put the center in their Rallys, anywhere you need them to be, that is physically possible. I paid about $110 per wheel for custom bs 10's,back in 2004, from Jeg's. They come primered.
 
I used 15x7 with 4 1/4 backspace. That's as wide as I can fit on my 69 Dart. I suggest that you do some measuring. All these cars are different. Mine came from Wheel Vintiques. They were made the way I wanted, but it took 2 months I think.
 
What axle? Going to LBP (this is on an 8-3/4) and the drums they require will require you to add to your backspacing.

For example, my 8-3/4 with 11" drums, a 17x8 wheel required a 5.375" backspacing to fit a 245/45/17 tire on my car. This is with stock location springs.

To run a 255 wide tire, you'd better look to 8-9" wide rims, preferably 9". Do as AJ said, add the 3/4 offset, install you LBP axles and brakes and then measure.
 
Well my axles and brakes are installed, they are custom to use factory abody drums that are re drilled.
 
255/60 are 10" wide. 12mm offset is a 1/2". Your tire would be 5 1/2" from mounting surface in towards the springs and 4 1/2" toward the fender lip.
 
I have 2 15x8 with 5" BS that were on my Dr Diff LBP axled 8 3/4. Since I am running 275s, it was too close to the fender for my liking. If you are interested in them, PM me.
 
domdart said:
255/60 are 10" wide.
Click to expand...

Not necessarily. That number, the section width, changes by tire manufacturer, model of tire, etc. For example, BFG T/A's in a 255/60/15 (the only tire that tirerack sells in that size) list a 10.2" section width. With 255's on a 70+ Dart that makes a big difference, because on most 70+ Darts with the stock spring locations there's only about 11" from the inside of the quarter to the spring. That extra .2" basically means your tire has to be perfectly located to not rub on something, and even then ride height will come into play.

On my '71 with an 8 3/4, BBP axles and the stock spring locations I have 6" from the spring to the wheel mounting face and 5" from the wheel mounting face to the quarter. That's with axles intended for the later BBP brakes.

With axles using the A-body SBP offset and redrilled brakes it would probably be closer to 5.75" from the wheel mount to the spring and 5.25 from the wheel mount to the quarter. That's going the make a +12 offset a little too close to the springs. Remember, backspace is measured to the inside lip of the rim. So a 15x8" rim is actually 9" wide, and if it's got a +12 offset, and therefore has a 5" backspace, the outer edge of the rim is actually 5.5" from the mounting face. The tire is another 1/2" inside of that (it's at least 10" wide), so you're at 6" from the edge of the tire to the wheel mount. Actually 6.1" if the section width still turns out to be 10.2. With an A-body SBP axle offset +6 is more like what you need, which on a 15x8 is 4.75" of backspace. That should put a set of 255/60/15's right at the spring, and you can adjust your spring clearance with a small spacer to maximize your tire to quarter clearance, which needs more space than the spring.

If you have the brakes on your car now, you can use a carpenter's square to measure from the face of the drum back to the spring and out to the quarter and confirm your numbers. These cars are all a little different, and they're frequently not even the same side to side. My '71 Dart has an extra 1/8" of clearance on the passenger side than it does on the driver's side.
 
Ok, so with the brakes and axles bolted in,
Mounting flange of axle to spring 5 7/8"
Mounting flange to inner fender 6 3/4"
Mounting flange to outer wheel well 5"
 
twayne24365 said:
Ok, so with the brakes and axles bolted in,
Mounting flange of axle to spring 5 7/8"
Mounting flange to inner fender 6 3/4"
Mounting flange to outer wheel well 5"
Click to expand...

So you've only got 10 7/8" if you leave the springs in the stock location and don't do any trimming on the quarter lip. That's really not enough to run a 255. The section width on most 255's is close to 10.2". You really need about a 1/2" to the quarters to avoid rubbing, and the springs need a minimum of a 1/4", and that's really tight with a 15" tire. Not as much an issue with a shorter sidewall, but with a 255/60/15 you need to leave room for sidewall deflection. So, you're out of room if all you've got is 10 7/8".

To safely run 255's I think you'd need to run the offset spring kit. Keep in mind that Mopar Performance calls this a 3/4" offset kit, but it's NOT. The front hanger only moves in a 1/2". The rear shackles are offset 3/4", but you don't get a full 3/4" on the front of the spring. It's not physically possible, there's only a 1/2" of room for an offset between the stock hanger and the frame. That's why Dr. Diff calls his offset kit a 1/2" offset. It's better made than the Mopar Performance offset too. I have both, and wouldn't use the Mopar kit again.
 
With my calculations on my 72 scamp. I should be able to JUST run a 255 on a 15x8 with 4.75 backspacing. That is assuming 11 inch between spring and out wheel well inner lip. A 15x8 with 4.75 just centres the wheel in the well. The tire's I am after measure a 10.2 section width with 7.5 inch rim. Running the 8's should decrease that a hair.

That said. Before I get 255's mounted. I am going to go under, re-measure. And do the math. With your measurements. Like others mentioned. I would suggest the spring kit and maybe rolling fenders. If you are ok with that.
 
Lustle said:
With my calculations on my 72 scamp. I should be able to JUST run a 255 on a 15x8 with 4.75 backspacing. That is assuming 11 inch between spring and out wheel well inner lip. A 15x8 with 4.75 just centres the wheel in the well. The tire's I am after measure a 10.2 section width with 7.5 inch rim. Running the 8's should decrease that a hair.

That said. Before I get 255's mounted. I am going to go under, re-measure. And do the math. With your measurements. Like others mentioned. I would suggest the spring kit and maybe rolling fenders. If you are ok with that.
Click to expand...

Measure twice, cut once! :D

Definitely make sure you actually have 11", and check both sides. I have 11" on one side and 11 1/8" on the other, and that's without any rolling or trimming. But maybe the assemblyline gods shined on my car. 245 seems to be the limit for a lot of the Darts/Scamps. Even with 11" from the quarter to the spring a 255 will be tight, stiffer springs and a rear sway bar would go a long way to keeping the tires off the body. With worn out stock springs and no rear bar it might not be enough.

twayne24365 said:
Thanks fellas, my quarterblips are rolled as well
Click to expand...

The quarter lips are rolled and there's still only 10 7/8"? Dang. You did not draw the good tire clearance card from the factory assembly line. Unless you offset the springs I would stay with a 245.
 
Well it's 10 7/8 up inside the wheel well where it starts getting narrower, its more like 12" at the wheel lip. Which will actually be about where the tire sits with the superstock springs I put on last night.
 
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