Adam if memory serves, backspace is easy to find, but offset is a little harder and more obtuse. To find backspace, lay the wheel face down. Put a straight edge across the back lip and measure down to the hub mating surface. Not real sure of an easy way to find offset, though. The definition of offset is the difference of the vertical centerline of the wheel and the hub mating surface.

Here's a couple links with pics to splain it better...

Offset picture

Backspace measurement illustrated

Cute little article that goes with the pics

A supposed backspace/offset calculator that kinda baffled me...

Hope those help <img src="/forums/images/graemlins/kewl.gif" alt="" /> Those wheels look badass <img src="/forums/images/graemlins/mrt.gif" alt="" />

Fasteddy's advice is occasionally sound...