hey yall i just put on my new 18x8 oz racing f1 cups, and i was wondering about the speedo being messed up. i have 225/40/18 tires on them, and my friend said that should fit the standard that came on my car. its a 97 gxe. thanks for the help guys (and gals)

casey

 

If your tires are 225/40/18, then the overall diameter of the rim/tire will be a little smaller than the stock rim/tire. The speedo will read faster then you are actually going (speedo will read somethin like 50mph instead of actual speed of like 48). The ideal tire size that will match the stock rim/tire size is 235/40/18.

 

ok thats cool, as long as im not moving faster than the speedo says i am i wont worry

yeah i wanted 235/40/18 nitto 555's but i wuz ganna have to order them plus they were a lot more money so i got what they had in stock. 225/40/18 dunlop sp-10's. its what i had on my other rims (17's) and i liked them.

casey

 

I have 225/40/18 on mine, and it is 1 mph under over the speed limit. I'm not too worried about it, and the dealership wanted something like 240 bucks to recalibrate it. I think I can manage that 1 mph
Hope everything works out for you.

 

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

You can plug in the numbers and it'll tell you how much you're over/under.