How to Calculate Gearbox Torque

Written by ryan menezes
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How to Calculate Gearbox Torque
As seen in this cutaway, a gearbox's torque depends on the size of its gears. (old gearbox dumped in a rest area on the side of the road image by Undy from

Your gearbox produces a greater torque than that which enters it. The crankshaft's flywheel, which the engine's cylinders rotate, applies a torque to the gearbox's primary gear. The gear then turns a smaller counterpart with fewer teeth, rotating it with a greater speed. The car's driveshafts then carry this increased torque from the transmission to the rotors of the wheels, giving them enough force to drive the vehicle forward.

Skill level:


  1. 1

    Multiply the force applied to the box's first gear by the first gear's radius. If, for instance, 2,500 Newtons act on a gear whose radius measures 0.5 meters: 2,500 x 0.5 = 1,250 Newton meters.

  2. 2

    Divide the radius of the first gear by that of the second. If the second gear's radius measures 0.1 meters: 0.5 / 0.1 = 5. The gearbox's torque ratio is 5:1, and its torque multiplication factor is 5.

  3. 3

    Multiply the last two steps' answers: 1,250 x 5 = 6,250 Newton meters. This is the gearbox's torque.

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