[Danger Dude]

here is a tire calculator that also gives you speedo change

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

 

[Danger Dude]

Dom you are post ho'ing

 

[Danger Dude]

Here play with this tire calculator and determine what you think will look best.

Tire size calculator

 

[Danger Dude]

No somebody posted first because it came in my email then they deleted the thread.

 

[Danger Dude]

. in my oppinion 17's are better because 18's are heavy.. my car feels even slower do to the extra weight and rotational mass..

That is because you are slower. The additional weight of 18's and more rubber on the tires adds nearly 100 lbs to the weight of the car. You will mostly notice this when you first accelerate from a stop.