Maybe I am getting a bit carried away. BUT I FOUND OUT!!!

The tires that came on my civic were 22.1" 943 Revolutions per mile Michelins with 9/32" tread depth. Michelin is a FRENCH company that doesn't like putting any of their product specifications on-line. I had to go to a tire store to find out their specs. :angry:

If you can't get the tire's rev's per mile, but you can get the diameter...

Take the overall tire diameter and SUBTRACT twice the tread depth. Multipy the adjusted diameter by pi (3.14). Divide the number of inches per mile by the circumference. The answer is the number of rev's per mile.

(D - 2(tread depth))3.14 ÷ 63360 = revolutions per mile.

That size is difficult to match outside of low-end econo-radials. You're supposed to stay within 3% of the OEM diameter or you'll throw off your speedo and cause the geometry of your suspension to change, hurting its performance.
Here's how you find out how far off your speedo/odo will be per mile...

Take the larger tires' rev's per mile, divide it by the smaller tire's rev's per mile. The answer is a percentage that you can multiply by what your speedomoeter reads and it will give you the actual speed you're traveling. If the larger tire is being substituted, you'll be going faster than your speedometer reads.

For example, take NITTO's smallest diameter 17" tire... NT-450 205/40ZR17. It turns 886 revolutions per mile. 943/886=1.064334 or 6.4334%. If your speedometer says 80mph, you're really going 85.14673 mph.

So there you go. Tire tech that everyone can use. Thanks for putting up with my babble.

Jafro