The closest 15-inch tire to stock is a 195/55/15, which is 23.4 inches in diameter. The 50-ratio 195 tire is about .76-inch smaller in diameter, but will provide sharper steering and a slightly higher indicated speed. The best 195/50/15 tire is the Goodyear GSD3 at $93 each. I would bet that this tire is better than any 205/50/15 tire as far as handling is concerned, so if I had the choice, I'd go with the D3s.

 

Incorrect.
The stock tire is 23.2 inches. 195/55/15, at 23.4 are .2 (almost a quarter inch) different than stock. 205/50-15's are23.1 which is only .1 (less than an eighth inch). Here is a pretty good link to compare tire sizes. http://www.miata.net/garage/tirecalc.html

 

I stand corrected, but really, a .1 or .2-inch is nothing compared to the overall diameter (0.9%)!

 

tire pressure has a larger effect that what you guys are talking about, don't always go by some calculator because different brand tires of the same size have different overall diameters as well as tread depths. the big factor of tire size is the width of the rim, which he didn't offer in the first post. if it's a 6 in rim, then a 195/(55,50) will do fine. if it's a 6.5, then a (195,205)/50 will do. if it's a 7 inch rim, then a 205/50 will do fine.

note: the tiny differences that you guys aren't going to affect the speedo by that much, after about a 3-5% change, that's when the mileage is a problem.

 

Good point on therim width. Should've added that to the equation.[sm=smiley20.gif]

 

I was told by a Tirerack rep that a 5.5-inch wheel can accomodate up to a 205/50 tire. many of the light 15-inch wheels are 5.5 or 6 inches wide.