When I installed the 15" Audi 5000 wheels (with Nokian WR 205-65R15 XL tires) on our van I had a local machine shop make up four 1/2" spacers.  I brought in one of the Audi rims and the machinist made up the spacers to match the mating surface of the back of the rim.  He ran the aluminum stock through a planer to make sure the front and back surfaces were parallel.  I glued the spacers to the rims to make rotating tires easier.

George
'85 Westfalia