72 Plymouth Duster Backspacing

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