LOL......Confusing isn't it Mario..Backspacing is part of offset. Yeah, those goofy clowns down in Madision....I think they really do enjoy using my tax dollars for toilet paper.
To explain offset, with a car wheel with 0 offset, the hub/mounting surface is centered (widthwise) in the middle of the rim. A postive offset, the hub/mounting surface is further to the outside of the rim. Negative, hub/mounting surface is towards the inside of the wheel past center..
Backspace.....Take an 8 inch wheel, say the offset is 0 (hub/munting surface is centered/widthwise). That would mean it has a 4" Backspace (half the wheel width) If the wheel had a +13MM offset (about 1/2") that would mean that rim now has a 4 1/2" backspace. Vise versa for negative. If the wheel had a -13MM offset, now the hub/mounting suface is deeper down in the rim 1/2". So 1/2" - 4", you would have a 3.5" backspace.
Make sense or do you now have a bigger headache?
Thanks again for lending your idea on the rims! I've decided to go that route...Keep the meaness in it!! Question is now, do I go with the 17" like is on the Charger or should I stick with the 15" and taller tire sidewall, like is on the car now?