Motorcycles are beautifully simplistic. For a chain-drive bike, circle a chain around that sprocket and another sprocket attached to a wheel, and away you go. The fun part for bike owners is that it’s easy to play around with those sprocket sizes to change the personality of their rides. The size relationship of one sprocket to the other yields the final drive ratio, which determines how much speed results from the engine’s work.
Count the teeth on the rear sprocket. Each time this sprocket makes one revolution, the rear tire makes one revolution.
Count the teeth on the front sprocket. This part isn’t quite as easy, as the front sprocket is hidden. If your bike is still stock, you can find the stock sprocket sizes in your owner’s manual and some recommendations and warnings related to changing those sizes. If your bike was bought used and you suspect it's been modified, you'll need to remove the front sprocket cover. This may require removing fairing covers or even the gear linkage if your chain drive is on the left before you can reach the sprocket cover.
Divide the number of teeth in the rear sprocket by the number of teeth in the front sprocket. This is your final drive ratio.
