Bigger Rims = Speedo Off?

[pierrebond]

If I put some 18s on my c230 which comes stock with 15s, my speedometer will be off? How do I recalibrate this if so?

[marsbike]

as long as the OD of the tire is the same, or really close, it should be fine.

[pierrebond]

Awsome thanks! Seems I'll need something like 225/40/18 for a tire size then.

[c55m8o]

Try this handy tool...

http://www.miata.net/garage/tirecalcold.html

since it's Javascript, you can actually use IE's save complete or save single file feature to save this locally and re-use it from your local computer.