Gear ratio

A gear ratio compares the rotational speeds or tooth counts of two meshing gears. It determines how rotation speed and torque change between the gears.

Angular velocity: Angular velocity is the rate at which an object rotates, measured as angle per unit time. A gear ratio relates the angular velocities of the two meshing gears.
Gear: A gear is a toothed wheel that transmits rotary motion through engagement with another toothed part. Gear ratio arises from the interaction of two gears.
Transmission (mechanics): A mechanical transmission transfers power and motion between a source and a load. Its gear ratios adapt engine or motor speed to operating demands.
Belt drive: A belt drive transmits rotary motion between pulleys using a flexible belt. Pulley diameter ratios can change speed without meshing gear teeth.
Torque: Torque is the turning effect of a force about an axis. Ideal gear trains trade rotational speed for torque according to their ratio.
Gear tooth: A gear tooth is a projecting part of a gear that engages teeth on another component. Each tooth that passes the mesh constrains the motion of the opposing gear.
Bicycle gearing: Bicycle gearing is the arrangement of chainrings and sprockets that sets the relationship between pedaling and wheel rotation. Tooth-count ratios determine how far the bicycle travels per pedal revolution.
Chain drive: A chain drive transmits motion between toothed sprockets using a linked chain. Its sprocket tooth counts set a ratio much like meshing gears, but with a flexible link.
Gear train: A gear train is a set of interconnected gears that transmits motion and power. A gear ratio describes one mesh or the combined transmission of a gear train.
Pitch circle: A pitch circle is an imaginary circle on a gear used to define its effective rolling motion against a mating gear. Its diameter connects gear size to tooth count and meshing geometry.

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