Here's some info that may be helpful. For a 2004 bike with 32 tooth pulley the following formulas should help you convert from mph to rpm and back:

RPM = (gear ratio x mph) / .0206

MPH = (.0206 x RPM) / gear ratio

Gear ratios are as follows: 1st = 2.375; 2nd = 1.579; 3rd = 1.16; 4th = .906; 5th = .75

An example: 80 mph in 5th gear = (.75 x 80) / .0206 = 2913 rpm

Another example: 3000 rpm in 4th gear = (.0206 x 3000) / .906 = 68.2 mph

Additional info: Factor is based on standard rear tire size (150 x 80 - 16) which has a circumference of 6.659 feet. Primary transfer ratio is 1.532 and secondary transfer ratio is 2.393. Factor calculated as follows:

.0206 = ( 1/ (1.532 x 2.393)) x 6.659 ft/rotation x 60 min/hr x (1 mile / 5280 feet)

(If you're running a 31 tooth drive pulley, your secondary transfer ratio would be 2.47 and factor would be .0200.)

Hope this helps and hope my math is ok!<br><br>Post edited by: pday, at: 2006/08/25 11:24