Originally Posted by BlownGP
Backspacing is measured in inches not mm and is the distance from the back of the rim to the hub mounting surface. Offset is the distance between the hub mounting surface and the center line of the wheel.
Stock offset is 20mm
I know the difference between offset and backspacing, I worked in and managed a tire shop for almost ten years. I just used that terminology inadvertently because that's the way the OP worded it. Thank you for the clarification, however.
And since we are being precise to the last millimeter, the exact offset of the 20" RAM wheel is +19.04 mm, not 20 mm, which is actually an erroneous measurement anyway, since you did not indicate whether it was a positive or negative offset.