Deve how did the rims look from Wheelsmith? What backspace did you get? 3.25 or 3.5? Im going to order mine from them soon, Im going to stick with 16" though (Chrome Smoothies). Hope this comes through it is a tire size calculator a friend gave me the link for. You can plug in the old and new and it will show you the tire differences.
http://www.miata.net/garage/tirecalcold.html
