I am getting ready to purchase some new tires since mine are almost gone.

I currently have 235/45/17 on my 7.5" wide Chrome Rims. I know I can fit a 245 since Kumho says it will fit. But do I get a 40 or a 45 series? I dont want to throw my speedo off by too much. Plus I dont want it too small or bigger than the original outside diameter of the 225/50/17 wheels it came with.

Pretty much all I am concerned with is the OUTSIDE diameter of the tire and wheel installed. That is all that really matters.

 

245/45/17 is within .685 % of the stock 225/50/17 tire size, while 245/40/17 is close to 4% off. Get the 245/45/17 tires.

 

Where you get this info from? It is universal info? Cause I want to upgrade to a larger rim size and tire on my other car also.

 

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

use this for all your tire sizing needs

 

That joint is the BOMB!!!