Thank you Mike for this tutorial,hope you'll post on your website (it's easier for me if i need go there than explore all Moi's threads )
you technique can be useful in many other situations
I've opened your 3DM file than export in OBJ:i've found few areas where mesh is not regular (that's normal in complex surfaces)





this can generate artifacts when render so i choosed a complex lighting set-up:open space-sun-real asphalt floor and also applied a glossy white material for the rim
(i've just modeled 3 different rims and tires so i mounted my PIRELLI P7 on your rim)



i also did a close-up shot to see if appear any artifact:it's OK...although a not-perfect mesh
(maybe a stronger close-up should show the problem,but..you see the whole wheel or the car,not a little imperfection in a little area of the rim)



thanks again:M