72bluNblu, quick easy question...If I have a 17x8 wheel with 5.75" backspace, and I add a 3/8" spacer am I increasing or decreasing the backspace? I forget how it works. That would make a 17x8 wheel with an effective BS of 6.125 or 5.375 ?
You're decreasing the backspace by adding a spacer. So, if you start with 5.75" and add a 3/8" spacer you'd end up at 5.375".
That's why I prefer to err on the side of having a little too much backspace. You can add a spacer to move the wheels off the frame/springs/suspension. But if you don't have enough backspace, all you can do is modify bodywork or buy new wheels.