hi, i just bought my S 00 about a month ago and i'm planning on changing the rims. i'm planning on getting 18's but do not know what tires sizes to get or how big can i get them. Anyone know what is the max size i can get for the front and back on 18's? thanks in advance

 

You are forgetting a couple of critical details. Tire size depends upon the width of the rim, the offset of the rim and whether or not you have or even plan to have a lowered car.
You can also go to the TireRack site and punch in "S2000" and select 18" rims to see what possibilities there are.

(A better question will get you a better answer.)