Most of the motor kits sold for 26 in. wheel bicycles seem to come with an over all reduction of approx. 17:1 - 20:1 . The chinese 2-stroke kits/motors have a 4.2:1 primary reduction built into the motor then an 11t output sprocket to a 44t driven sprocket at the rear wheel. The 4-stroke kits usually come with a primary reduction gearbox with a reduction in the neighborhood of 3.7:1 then an 11t output sprocket to a 56t rear driven sprocket for an overall reduction of 18.8:1. Reduction is just a math problem. Divide the larger dia. driven sprocket/pulley by the smaller dia. driver sprocket/pulley. With sprockets you count teeth with pulleys you measure dia. So say you had a 2 in. dia pulley on your motor you would need a 40 in. dia pulley at the rear wheel to get an overall reduction of 20:1 The driven pulley is larger than the rear wheel. Hence jackshafts or reduction gearboxs come into play. Due a search for the Ratio Calculator here on this site, its a very useful tool to work alot of this out. The Dia. of the whizzer Sheave is 17 in. - 18 in. I believe?
ocscully
