moves the drop center ty the back side of the wheel so the bigger lip is natural. This is very common with multi-piece wheels because there is more room for the drop center on the larger portion of the wheel. Some one-piece wheels are also reverse but this is for cosmetics only. It lets you have a large lip withouth the steps for the drop center.
What is a very safe offset? The 18X10 fits best with a 45mm offset. This gives clearance on the rear spring and brings the outside lip right even with the fender. If he went much different the wheel would rub the spring or stick out like a Homie-G ride. What I'm trying to say is he got the largest lip on the rear he possibly could in that wheel.
