Looking to make some type of "informed decision" on some bargain rims for my old XJ and was looking for the definitive answer on what " negative or positive back spaceing I should be looking for with my current modest 4-inch lift and 31 inch tires and a later purchase of something like the BFG 33-incher-I am confused by an additional term called "offset"-I understand vaguely that different rim manufacturers use different reference points to explain their product but I am just at a loss to understand what rim I will be needing-Again any and all advice/suggestions appreciated-TIA