I am looking at buying new wheels for my 03 cobra. The IRS bolt has been grinded. Looking for the maximum and minimum of offsets and backspacing I can go with while sticking with a 305 or larger width? without smacking my brakes and rubbing anything. I want something like an enkei wheel or oz so I need to see what I can work with

 

You will need a 6.8" of backspace on a 10.5 wide wheel. If you are lowered and want to run less, roll your fender lips. I believe you could go as little as 6.3" of backspace. Any less, and the tire starts to leave the fender well. If you want to run a 10" wide wheel the backspace will be similar but the 6.3" of backspace will keep the tire closer to the outside of the wheel well. this is based on a 315 tire.