Need help in Rim Size selection

[Townsend_xB]

Ok, I want to get: Tenzo R Overdose Rims in Hyper Black for my xB What size would be identical in size to the stock OEM Rims? 17 or 18's? I cant figure this out and the guy from wheels next said that either would fit my car but I want to be able to use the Donut as well as not change the speedometer or odometer Thanks for your help in advance

[dexter_5000]

http://www.miata.net/garage/tirecalc.html use that it helps in deciding the larger the wheel the smaller the tire profile will be. i recommend staying with a 205/45/17