like title says, just put in 18's and was wondering if i have to take my speed into consideration...ive heard now if i see im going 40 im probably going 50, is this right?

 

What size tires?

 

You should be keeping the overall tyre diameter the same. Otherwise the tyre/wheel combination will ruin your wheelwells if it is too big, or will be too small. The speed difference is negligible.

 

fronts are 235/40 and rears are 265/35. i did my research and this is the most you can go without doing additional mods. the speed difference was just my main concern. gracias pablo

 

Depending on the tire model, a 265/35 18 will read about 2-3 miles under your real speed per 100 mph. Those numbers might not be exact, I'm too lazy to do the math right now. In otherwords, not that big a deal.

 

~1.2 MPH speed difference.

 

Pedro, did you change your name to Pablo?????

 

my bad, that should be pedro... sorry about that

 

Just use this handy tire size calculator program.

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

Mark

 

thats pretty sweet ^^
thank you fellas