The chain drive.
- chainring (front sprocket)
- Chain with attachment to the hub (rear sprocket or sprocket)
Many bicycles are equipped with a gear hub or derailleur system. These parts are covered in separate articles.
The chain drive on the bike is very efficient. The efficiency of a well-lubricated gear drive (chain and bearings) is around 98.5%. Also, the muscle consumption efficiency through the chain drive is high and is very close to the theoretical maximum. Many people wrongly assume that the circular pedaling movement is inefficient. The leg strength is, after all, always downward, while only perpendicular of the force on the pedal provides the propulsion (see Figure 1) . The force along the crank has lost power. Exerting a force must not be confused with the performance of work.
The force x distance traveled is labor.
The application of a force directed along the crank costs no energy. Attempts to create more efficient muscle use, the leg strength while going around deliberately to move perpendicular to the pedal, have failed. Also structural changes in the drive such as the biopace-chainring (oval instead of round) have not led to a higher yield of muscle use.
Alternatives to the drive as belt drive and shaft drive on bicycles should therefore be viewed very critically. The chain drive efficiency alternatives usually get nowhere near. Since the power is limited on a bike, its systems on a bike have unacceptably large losses.