72 Plymouth Duster Backspacing

[Ivoryk3ys78]

Before ordering some new mag wheels I did some searching on here and there seemed to be consensus that 4.5 backspacing on a 8 inch wide rim would allow a 275/60/15 to fit on the Duster without issue. Several people posted they did it without problem.

I ordered the mags and we put my dads 275 on and no way it would fit. The deep backspacing put mt ridght against the springs on the passanger side and on the drivers side even worse. Luckily they will work great for my brothers 67 Satelite to fit 255/60/15 so he will buy them from me.

So now today we tried to mount up some old slicks my dad has for his Roadrunner onto the Duster to see if they fit to buy new slicks for the wheels. They fit just fine and they are the size of a 275. These rims are a 3.5 backspacing.


I am wondering what would make my setup different? Why does that deep backspacing seem to work so well for others but for me im against the spring and a 3.5 backspacing works much better.

Thanks

Oh and I have 8 and 3/4

 

[72bluNblu]

Large or small bolt pattern?

If it’s an A body 8 3/4 with the stock SBP axles then 4” is usually a better backspace. With BBP axles and a 15x8 with 4.5” of backspace you should be fine. 3.5” of backspace only works if the car is sitting fairly high in the back, at stock ride height that usually put the tires into the quarters.

And there’s always the wildcard, the axle could have been shortened.

 

[Ivoryk3ys78]

Thanks. Yeah no way in the world would 4.5 backspace work for me. We even tried a 3/8 spacer and the tire still hit the drivers side spring.

It is a 4.5 bolt pattern. The springs are XHD from Mancini I bought a couple years ago. The car definitely sits pretty high in the back.

Yeah.. maybe someone did shorten the axles before we got it.. I guess anythign is possible.

Right now I have 3" backspace on I believe a 7 inch rim with 255 that works well but 3.5 will definitely work with 275.

Large or small bolt pattern?

If it’s an A body 8 3/4 with the stock SBP axles then 4” is usually a better backspace. With BBP axles and a 15x8 with 4.5” of backspace you should be fine. 3.5” of backspace only works if the car is sitting fairly high in the back, at stock ride height that usually put the tires into the quarters.

And there’s always the wildcard, the axle could have been shortened.

 

[72bluNblu]

Thanks. Yeah no way in the world would 4.5 backspace work for me. We even tried a 3/8 spacer and the tire still hit the drivers side spring.

It is a 4.5 bolt pattern. The springs are XHD from Mancini I bought a couple years ago. The car definitely sits pretty high in the back.

Yeah.. maybe someone did shorten the axles before we got it.. I guess anythign is possible.

Right now I have 3" backspace on I believe a 7 inch rim with 255 that works well but 3.5 will definitely work with 275.

With a stock width A-body 8 3/4 and BBP axles installed it should be about 6" from the face of the drum where the wheel mounts to the springs.

So, 4.5" of backspace, with a 275 you should have about 1" of tire overhanging the lip of the rim at the section width, so that's 5.5", leaving a good 1/2" to the springs for clearance. That's how it should work.

Sounds to me like someone shortened your axle.

 

[Ivoryk3ys78]

Will measure next time I am down at my parents or will call and have my dad measure. Could there be something different with the pumpkin? Is there an A and B Body 8 3/4 that would make a difference?

With a stock width A-body 8 3/4 and BBP axles installed it should be about 6" from the face of the drum where the wheel mounts to the springs.

So, 4.5" of backspace, with a 275 you should have about 1" of tire overhanging the lip of the rim at the section width, so that's 5.5", leaving a good 1/2" to the springs for clearance. That's how it should work.

Sounds to me like someone shortened your axle.