Originally Posted by Rob 93ZR1
Looking to replace the stock 20" wheels with aftermarket 17" rims. I would like to better understand offset and backspacing, but need a starting point. If the OEM wheels are 17x7 with a +1 offset, does that mean the backspace is 4.5"?
That's not correct. What you're missing is that wheel widths are measured bead to bead but backspace is measured from the lip. The lip is normally 1/2" past the bead so that needs to be added in. Add 0.5" to your 4.5" and you'll come up with the correct 5" BS for that wheel.
Here's another calculator that I like for comparing tire/wheel installations. http://www.rimsntires.com/specs.jsp