wheel spacing

[booyaballer]

my 70 challenger currently has 14" magnum wheels which appear to have 3 3/4" backspacing (if i measured correctly). it also had 1 1/4" spacers and drums on all four corners.

I'm changing to 15" police chrysler wheels 15 x 7 front and 15x8 rear all with 4" BS, based on reading the forum. i'm also adding front disc brakes ( stock reproduction type disc). now to my question, how do i determine how much backspacing i need?

Thanks in advance.

 

[Coupe]

Ive never done this from scratch before. Ive always had different combinations of wheels to test with.
On the front, try a stright edge across the mounting surface. Measure from it to the sreering arm and any other suspension or break part that might drag the steel wheel. I would then subtract 1/2".
On the back, you could do the same, Dosn't sound like your choice for the rear is too much. Too much back spacing on the rear can drag the tires on the inner body.
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