I want to say that since the wheels are Trigo cobraII wheels that came with the car from Shelby a few years ago, these should be the standard 3 ½ inch backspacing. I am selling these wheels for my father-in-law and since we are both not the most knowledgeable on the subject, I mesured the wheel myself in an unsophisticated manner using a straight edge and a ruler. Measuring according to the procedure from
http://www.rsracing.com/tech-wheel.html or
http://www.high-impact.net/wheels/ho...ckspacing.htm, I seem to get a backspacing measurement of approximately 3 5/8 inch for all four wheels. If you are interested, I could call and ask the mechanic that installed the new 17inch wheels and most likely find out a more potent answer to this matter. I hope this helps with question. Also, I have edited the original post and lowered the price.