i was looking into the NT555...good grip...good tire wear...problem is that i went on their website and they don't have 225/50/17 and 235/50/17...could i go as low as 225/40/17?...what would be if any, adverse affects??

 

I wouldn't put those on my car. You are going to be greatly lowering the overall wheel diameter if you put those in the front and even worse in the back. If you run the same size front to back it will make your TCS and VDC very touchy in normal driving. Your speedometer will read off by quite a bit as well.

 

it's really hard finding tires just the right size for the oem 17s...the michelins pilots seem great but they are very expensive...i wanted something that performs well and has good tire wear..the nittos seem to be cheap enough with the performance and wear rating i can live with...i'm just preparing for the time my bridgestone potenzas get eaten away....

 

go up to 245's or 255's they'll fit just fine.

 

i wonder if going 245 or 255 will affect the speedo

 

Use this:

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

Plug in the numbers and it will tell you how much your speedo will be off.