Earl,
If you have the size tires you want to use and want to figure the off set, why not try what one guy here did. He bought some cheap spacers of varying thicknesses and put them on until he got his tires like he wanted them and then went to the tire and wheel place and had them make his wheel offset the thickness of the spacers. He took the wheel he used to do the measuring so they could see what he wanted.
Ron
