Gearchanging

Gearchanging refers to the process of altering the gear ratio between an engine and the drivetrain to suit different speeds and loads. It is a fundamental operation in most motor vehicles and many mechanical systems that use gears, including bicycles and industrial gearboxes. Gearchanging allows the engine to operate in its efficient RPM range while providing enough torque for acceleration, climbing, or maintaining highway speeds.

In manual transmissions, the driver disengages the engine from the drivetrain with a clutch, selects a different gear using a gear lever, and re-engages the clutch. Synchronizer rings help align gear speeds so each gear can engage smoothly. Upshifting reduces engine RPM and can improve fuel economy, while downshifting increases engine braking and helps with acceleration or deceleration without overusing the brakes.

Automobiles with automatic transmissions perform gear changes without direct driver input, using hydraulic systems, electronic control units, and torque converters or clutches to select gears. Modern automatics include dual-clutch transmissions, which use two separate clutches for odd and even gears to enable rapid changes, and continuously variable transmissions, which adjust the gear ratio continuously rather than in discrete steps. Automated manuals are semi-automatic systems that use actuators to operate a manual gearbox.

Gearchanging also occurs in bicycles, where derailleurs or hub gear systems move the chain to different front or rear sprockets to change the mechanical advantage. Across systems, efficient gearchanging improves performance, drivability, and fuel efficiency, while improper shifting can cause wear or damage to components.