Back Spacing for 17-inch Pin Drive

[MikeC]

Having tried some searches with mixed results, I would appreciate any help and insight from the knowledge base on this forum.

I have a Unique FIA 289, #9142, currently with 15-inch Compomotive bolt-on wheels originally on the car. My plan is to convert to Vintage Wheels BR17 pin drive wheels with the knock off pin drive adapters. The BR17 specs are:
17 x 8 with 4.35in backspace
17 x 9.5 with 6 in backspace
17 x 10.5 with 4.35 in backspace (deep dish wheel)
The pin drive adapter reduces the above back spacing by 0.4 inches leaving me with:
17 x 8 with 3.95in backspace
17 x 9.5 with 5.6 in backspace
17 x 10.5 with 3.95 in backspace (deep dish wheel)

I have completed some measurements and it appears I can fit the 17 x 8 and 17 x 10.5 inch wheels above, but I'm a bit concerned with final rear tire to fender lip clearance.

My questions are:
Does anyone have any advice on what the correct back space figures front/rear relative to wheel width will fit and provide the fender lip clearance?
Am I better off using the 17 x 9.5 in the rear?

I want to be cautious since I am ordering from across the country and would like to get this right.

Thanks very much for any help and advice.

Mike

[RJacobsen]

Mike,
I’m not sure that you will get an exact answer to your question. I think that wheel type (bolt on or knock off) was a factor in the choice of axle length during the build of the cars. You should be able to compare the wheel offset that you currently have with what you are looking at in the new wheels and come up with what’s right for your car.

[MikeC]

Thanks for taking the time to reply.

It was probably a stretch to expect others to be able to supply the info since it is best I do all the right measurements since I'm deviating from the norm. I am comfortable with that. Was just hoping for some experience from others since I am new to the Cobra.

Interesting though that the interference point with a 17-inch wheel toward the inside will be the attachment point of the trailing arm to the hub. Other than that i was surprised to find a lot of room for a wider wheel as long as the back spacing does not push the wheel out too far toward the fender.

Thanks again.

Mike