I'm looking at an 18 x9 wheel. but the only other thing I can find is that they come in 0 or a 12 mm offset. what in the world does this mean. I can't find anything about backspacing, or is that the offset ? please forgive my ignorance on the subject.

 

Here is a place to learn what they are.

https://www.rsracing.com/tech-wheel.html

 

thanks kingfish. gotcha now. offset is just the measurement from the hub to centerline of the wheel, then take into account the wheel width to figure backspacing. clear as mud now. thanks again