In the case of bicycle chains, it is possible to modify the overall
gear ratio of the chain drive by varying the diameter (and therefore, the tooth count) of the sprockets on each side of the
chain. This is the basis of
derailleur gears. A multi-speed bicycle, by providing two or three different-sized driving sprockets and up to 12 (as of 2018) different-sized driven sprockets, allows up to 36 different gear ratios. The resulting lower gear ratios make the bike easier to pedal up hills while the higher gear ratios make the bike more powerful to pedal on flats and downhills. In a similar way, manually changing the sprockets on a motorcycle can change the characteristics of acceleration and top speed by modifying the final drive gear ratio. The final drive gear ratio can be calculated by dividing the number of teeth on the rear sprocket by the number of teeth on the counter-shaft sprocket. With respect to the stock gearing on a motorcycle, installing a smaller counter-shaft sprocket (fewer teeth), or a larger rear sprocket (more teeth), produces a lower gear ratio, which increases the acceleration of the motorcycle but decreases its top speed. Installing a larger counter-shaft sprocket, or a smaller rear sprocket, produces a higher gear ratio, which decreases the acceleration of the motorcycle but increases its top speed. ==Chain tracked vehicles==