Gearshifts

Gearshifts refer to mechanisms and actions that change the gear ratio between the engine and the drivetrain, allowing the powertrain to tailor torque and speed to driving conditions. The term covers manual and automated systems across road vehicles and, in a general sense, bicycles and motorcycles.

Manual transmissions use a clutch and a gear lever to select fixed gear ratios. The driver disengages the clutch, moves the shift selector through a set pattern to engage gears, then re-engages the clutch. Synchronizers help mesh gears at certain speeds. Benefits include direct control and potential efficiency; drawbacks include required skill and driver effort.

Automatic transmissions rely on hydraulic or electronic control to choose gears, using torque converters or clutch packs with planetary gearsets. Modern automatics use electronic shift logic, adaptive programming, and sometimes multiple modes. Variants include continuously variable transmissions (CVTs), which vary the effective gear ratio endlessly, and dual-clutch transmissions (DCT) or automated manuals, which use two clutches for faster upshifts.

Motorcycles typically use foot-operated or hand-operated gear shifts with sequential gearing and often sport quickshifters or electronic controls. Bicycles use derailleurs or hub gears with indexed or friction shifting to change chain ratios.

Maintenance involves checking transmission fluid, clutch wear, linkage alignment, and ensuring smooth engagement. Improper shifting can cause wear or damage. The choice of gearshift type affects efficiency, performance, cost, and driving experience.