gearing

Gearing refers to the arrangement of gears in mechanical engineering to transmit power and motion between rotating shafts.

A gear train comprises two or more gears that mesh so that their rotational speeds and torques are related by the gear ratio. The gear ratio is equal to the number of teeth on the driven gear divided by the number of teeth on the driving gear; the output speed is the input speed times the inverse of the ratio, and torque is multiplied accordingly. In involute gear profiles, contact remains near-constant, preserving the velocity ratio over a range of center distance.

Gears are categorized by type. Spur gears have straight teeth and simple alignment; helical gears have angled teeth for smoother operation; bevel gears transmit motion between non-parallel shafts; worm gears provide high reduction in a compact form; rack-and-pinion devices convert rotary motion to linear motion. Planetary gear trains use a central sun gear with planet gears to achieve high gear ratios in a compact package.

Key design considerations include gear pitch, module or diametral pitch, backlash, efficiency, lubrication, and load handling. Material choices range from various steels to cast iron and specialized composites, with surface finishing and bearing supports influencing life, noise, and reliability. Applications span automotive transmissions, industrial machinery, clocks, and bicycles, where gear selection (cogs, chainrings, and derailleur affordance) determines available ratios and performance.

In finance, gearing (financial leverage) describes the ratio of debt to equity and indicates the degree of borrowing used to fund assets. Higher gearing can amplify returns but also increases solvency risk during downturns.