Back Spacing Question

[MDC1969]

This form has been a great resource and has gotten me dialed-in pretty close. Since I know the width of my wheels, the offset will be a mathematical function of backspace and I do know the caliper clearance. I'm getting custom billet wheels so once they are cut I have to own the success, or pain! I did purchase a tool to measure backspace, (Wheelfit Pro 45, it actually mounts the real tire to the hub) it was expensive but seemed to be a good insurance against the cost of custom wheels.

Thanks for the tips, particularly about the control arm clearance with the drop spindles! I had not considered this before. Perhaps I can share this tool I purchased with someone else who is having to make these costly decisions.