Front and rear are 3.75" backspace for the Halibrand type aluminum wheel.
I made an unusal discovery today while doing some wheel bearing maintenance and have a question related to this thread:
I had previously noticed one pin drive spinner snout that was slightly shy of flush (front passenger side) on P2174 while the other three were about ¼” proud when the wheels were seated. I measured the pin drive snouts and they were the same. So I measure the back spacing on the wheels and found one is 3.75” and the other is 4.25”! See attached picture. This makes a very noticeable difference in where they run in the wheel well. They are 6 pin Vintage Wheels HA17s. The fronts are 17x8.5. They were on the car when I bought it and these wheels and were purchased and installed by the previous owner. Sort of a bizarre error on Vintage's part to ship a pair of mismatched wheels. Wonder if Vintage will be willing correct the matter for me? They seem to have a good reutation on the various forums. Guess I'll find out.
The Vintage Wheel website says they are available in 3.75" back space unless for use with adapters, then they are available in 4.25", 4.65", or 5". I suspect they'll machine whatever you want.
So my question is:
Is 3.75" the common back spacing for 8.5" wide front wheels on SPF cars? The 4.25" back space wheel actual looks to be a better fit in the wheel well.
Is the back spacing measured from the outer edge of the wheel to the mounting surface? I just placed a straight edge across the rim and neasured to the hub surface.
I take it the SPF pin drive spindle is not considered a pin drive adapter? I'd usually call an adapter as that you would bolt on to a lugged hub/spindle assembly to adapt to pin drive. Is this correct?