Back Spacing, which way?

Frnknsteen said

I'm no wheel expert, but I have been doing a lot of research into what I need if when I convert my '67 to the big bolt pattern.

First question,.... Which drum brakes are you using? According to conversations I had with Cass at Doctor Diff, if you go to the big bolt pattern and use the 10x2.5" drums. it will increase track width by .3" per side, which makes sense with what you are seeing. He recommended going with 15x7 wheels with 4.5" back spacing. That will move the wheel 1/4" towards your leaf springs (from where you currently are), which from what you are saying, should put you at 3/4" from your leafs and 3/8" from your fender edge.

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I am using factory drum brakes. I think what Cass was trying to explain was that when switching to BBP axles the axle flange sticks out a bit more than the SBP axles do. I don’t know what that measurement is but the .3” that you mentioned was probably correct. The only thing on top of the axle flange is the thickness of the brake drum hat which is less than an 1/8”. So, the .3” that Cass referenced to may or may not include the hat of the brake drum.

All the posts I read that showed the 4.25 backspace did not mention what axles they were using and I didn’t even think to ask the question so I ordered the 4.25 backspace.

At 2am, and after a long day I was trying to understand backspacing and it was confusing to me too.

I want to stay with the 7” wheel and after your explanation and some sleep I think that clears it up. Using the 4.5 backspace would kick the wheel center section out a ¼" more, thus moving the tire inward to 3/4” from leaf spring and 3/8” from fender lip and that should take care of the issue. Wheel Vintiques doesn't offer a 4.75 backspace and I'm not sure if the trim ring would still fit at that point with a custom wheel being made.

I will order the 4.5" and see what happens. I guess I will find out on the test drive if it rubs at all.