Hi!

I have a set of 7"x15" alloy wheels that have backspacing of 86mm (offset -14mm). To figure out how big tires I can fit under my 1989 Caprice Classic STW, I would need to know the offset (and backspacing) of the original 7"x15" steel wheels.

No guesses, not even good ones, just facts, please :)

Well if you want just the facts. How about finding out just what your wheels do have then?

Take a wheel off the car. Lay a straight edge across the back side of the wheel and measure down to the mounting hub. That will tell you what you have.

What did the alloy wheels come from BTW? Are you sure they even have the right bolt pattern needed? Wagons and 9C1 Caprices came with a 5x5 inch "truck" bolt pattern. If the wheels you have came from anything else GM they should have only a 5x4.75 inch bolt pattern.

Well if you want just the facts. How about finding out just what your wheels do have then?

Take a wheel off the car. Lay a straight edge across the back side of the wheel and measure down to the mounting hub. That will tell you what you have.

Yes, I know how to do that; I was just hoping that somebody already knew the values I'm looking for. It seems quite odd to me that nobody knows the dimensions of original wheels.


What did the alloy wheels come from BTW? Are you sure they even have the right bolt pattern needed? Wagons and 9C1 Caprices came with a 5x5 inch "truck" bolt pattern. If the wheels you have came from anything else GM they should have only a 5x4.75 inch bolt pattern.
They have been serving my Caprice for over ten years (winters), so I'm pretty sure that they will fit :smile: The size of winter tires was 235/75R15, so it doesn't help me with this tire fitting problem.

They have been serving my Caprice for over ten years (winters), so I'm pretty sure that they will fit :smile: The size of winter tires was 235/75R15, so it doesn't help me with this tire fitting problem.

I made an assumption that you had procured some new wheels.

I will tell you that tire fitment is going to be a touchy thing. It's really a car by car situation. I was told that 275/60/15s would fit on all four corners of my 9c1. I even saw people running this combo. But they won't work on the front of my car. Any slight dip causes the front fenders to hit the tires. That's not a fun experience when your going anything greater than 10mph BTW. :smile:

I am currently running 275/60s on the rear. They are mounted on 15x8 in Wheel Vintques GM trcuk rallye wheels with a 3.75" backspacing.

That's about as big as I can fit on those wheels. A different backspacing for me would allow a some what wider tire. But these current tires are quite big.

I would guess that the stock backspacing is right at 4" if I recall discussions on the 9c1 list from years ago correctly. I would also say that a 255/60 is about as wide a tire as you should mount on a 7" wide rim.