This page is the best way to take a quick look at offset and backspacing. Offset Explained
As for if a 245/45R17 will fit, depending on the tire the rim width range is anythere from 7.5" to 9". The wheels we have listed on our website are all a garunteed fitment. Our techs measure vehicles with some high tech laser/cad system and take those drawings and match up what wheels will fit. To find out if another wheel will fit compering offsets and widths will help, but there's no other way then to try it and see.