Does anyone know the correct wheel backspace for a 1964 Jetstar (Convertible, if it makes a difference). I have all the service manuals for this, yet I don't see "backspacing" in any of the specs. I know how to measure the ones I have, unfortunately I have two different ones on this car.

I am considering a 15 inch rim. Any concerns anyone would like to vocalize, I am up for it. I am reasonably confident the bolt pattern is 4.75. Not sure what tire size will fill the well nicely.

Anything would be helpful, thanks in advance.

- Smooth

Smooth@smoothfx.com
www.smoothfx.com

 

No one? Could someone take one off their car and measure?

 

OK, as I've stated many times here, you really want to specify OFFSET, not BACKSPACING. Backspacing is dependent on the wheel width, offset is independent of the width.

ALL GM RWD cars through at least 1990 used wheels with as close to zero offset as possible. That means that the wheel mounting surface is centered with respect to the width of the rim. Backspacing is the dimension from the inside edge of the rim to the wheel mounting surface, and depending on the exact profile of the edge of the rim (this can vary), backspacing is typically the offset plus half the rim width plus about 1/4 to 1/2 inch. For a 7" wide wheel with zero offset, this would be 3.5 + 0 + about 0.25, or 3.75" backspacing. For an 8" wide wheel, this would be 4.25". You can see why I prefer to specify offset, since it is zero in both cases.

Yes, a J88 uses a 5 x 4.75" bolt pattern.

 

Thank you! I needed to know the starting point for stock because I plan on altering it a little bit. I just wanted to have some basic knowledge before I dove into this. To order wheels, they ask you questions about backspacing. I just wanted to make sure there wasn't something unusual about the stock set up. Everything else about this car is one model, one year only. So it's always good to be loaded with knowledge before you start something :-)

Again thank you for your help!

-Smooth

 

A little tight, but the ride awesome.

Before - After picks

 

Photo doesn't seem to be working

 

I edited the posting... how 'bout now?

 

Very nice!

 

For what it is worth: 6 to 12 millimeters of negative offset would have allowed me to put the skirts back on without modification.

I went with a centered offset, but the wider tire has to be aired down to get in the rear wells. They look badass, and I am growing to like the open well. Lowering the back one coil ring really sets it off.