What is wheel offset?
 

I just bought a second gen av and it has 22s on it. I have found a couple different tires but not sure if they will fit. The bolt pattern is the same, but the offsets are different. 1st gen offset is a little different than 2nd gen. Can anyone explain to me what an offset is and how to know if a rim will fit my Av? Thanks

It is the distance between the hub mounting surface and the center of the wheel.

Positive Offset
A positive offset occurs when the hub mounting surface is on the street side (the side you see) of the center line of the rim. Most factory rims will have this type of offset.

Zero Offset
When the hub mounting surface is centered within the rim, it is known as a zero offset.

Negative Offset
If the hub mounting surface is on the brake side of the center line of the rim, it is considered a negative offset or "deep dish".