Does anybody know what's the OPTIMUM wheel size for the car? The original (SLK320) had smaller ones. The 18" and 19" appear to be too large, and sized upwards for cometic reasons.

For explanation: I have a Miata roadster and thru trial and error of the tens of thousands of owners, the optimum wheel size is about 15", but no bigger than 16" for this car. (Motocross racers use 14" or even 13" wheels). Beyond that 15 - maybe 16" size there are all kinds of obvious performance issues, especialy acceleration reduction, and even handling suffers, the car is too twitchy.

With these huge wheels on the Xfire my concern is unsprung weight, and rotational inertia, adversely affecting acceleration, braking and handling. Per test reports, the Xfire already has a 25 to 30' longer braking distance from 70-0 than the Miata ('99) 130+ feet vs 161' (Car&Dr. 07/2003).

This posting is not for comparison purposes, both cars serve a completely different function for me, but I wonder if I should be looking for new (smaller) wheels. (Would help the tire replacement costs too when I think of it). No, I wasn't thinking of replacing the Miata with an Xfire roadster, unfortunately, the Xfire (roadster) just doesn't have THAT amazing feeling the Miata has.

Any ideas or actual experience?