John: do a search on back spacing or offset, there is plenty on this sight.
Most wheel manufactures have a website that explains it, usually with a chart.
I have a Street Beasts with 6 1/2" wide rims that have 5 1/2" back spacing or offset to the inside. About 4 1/2" is all I can really use, so I have a 1" spacer on the face of the axle. The tires/wheels I have on it now are just for rolling around in the shop, not driving.
You'll have to see how much "clearence" you have available. You may not be able to put as wide of a tire as you want. good luck!
