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The number of revolutions made by a gear compared to the number of revolutions completed by the driven gear. Gear ratios are calculated by dividing output speed by input speed (i=Ws/W) or by dividing the driving gear's teeth by the driven gear's teeth.

  • The gear ratio changes as the number of teeth in the meshing gear change. At the same time torque also changes.
  • Two or more meshed gears make a gear set or a gear train. In a gear system, speed reduction means torque increase.
  • Also, speed increase means torque reduction.
  • An example of torque increase is a car that has a gear reduction of 12:1 from the transmission or transaxle to the drive wheels. The crankshaft turns 12 times to turn the drive wheels once.

Automotive drivetrains generally use gearing in transmission which contains a number of different sets of gears that can be changed to allow a wide range of vehicle speeds and also in the differential, which contains the final drive to produce further speed reduction at the wheels. The differential contains further gearing that splits the torque equally in between wheels while allowing them to vary in speed when traveling in a curved path