Your best bet is the actually measure the outside surface of the tire with a string, and then lay out the string and measure it with a tape measure.
If you want to do it the other way (not as precise) is to measure the diameter of the wheel/tire combo and then multiply by 3.1416. This number is called pi.
Eric B.
Ottawa, ON, Canada
98 Mystique V6 5spd. Toreador Red
Modified Airbox with K&N drop-in, Cool Blue bulbs, Homemade solid brass shifter knob, Sony CDX-L300 head unit
http://photos.yahoo.com/LBuzzer/
