Manual transmission

A manual transmission (MT), also known as manual gearbox, standard transmission (in Canada, the United Kingdom and the United States), or stick shift (in the United States), is a multi-speed motor vehicle transmission system where gear changes require the driver to manually select the gears by operating a gear stick and clutch (which is usually a foot pedal for cars or a hand lever for motorcycles).

Early automobiles used sliding-mesh manual transmissions with up to three forward gear ratios. Since the 1950s, constant-mesh manual transmissions have become increasingly commonplace, and the number of forward ratios has increased to 5-speed and 6-speed manual transmissions for current vehicles.

The alternative to a manual transmission is an automatic transmission. Common types of automatic transmissions are the hydraulic automatic transmission (AT) and the continuously variable transmission (CVT). The automated manual transmission (AMT) and dual-clutch transmission (DCT) are internally similar to a conventional manual transmission, but are shifted automatically.

Alternatively, there are semi-automatic transmissions. These systems are based on the design of, and are technically similar to, a conventional manual transmission. They have a gear shifter which requires the driver's input to manually change gears, but the driver is not required to engage a clutch pedal before changing gear. Instead, the mechanical linkage for the clutch pedal is replaced by an actuator, servo, or solenoid and sensors, which operate the clutch system automatically when the driver touches or moves the gearshift. This removes the need for a physical clutch pedal.

A manual transmission requires the driver to operate the gear stick and clutch in order to change gears (unlike an automatic transmission or semi-automatic transmission, where one (typically the clutch) or both of these functions are automated). Most manual transmissions for cars allow the driver to select any gear ratio at any time, for example shifting from second to fourth gear, or fifth to third gear. However, sequential manual transmissions, which are commonly used in motorcycles and racing cars, only allow the driver to select the next-higher or next-lower gear.

In a vehicle with a manual transmission, the flywheel is attached to the engine's crankshaft, therefore rotating at engine speed. A clutch disc sits between the flywheel and the transmission pressure plate which is attached to the transmission input shaft, controlling whether the transmission is connected to the engine or not. The clutch pedal controls the pressure plate (clutch engaged – the clutch pedal is not being pressed) or not connected to the engine (clutch disengaged – the clutch pedal is being pressed down). When the engine is running and the clutch is engaged (i.e., clutch pedal up), the flywheel spins the clutch pressure plate and hence the transmission.

The design of most manual transmissions for cars is that gear ratios are selected by locking selected gear pairs to the output shaft inside the transmission. This is a fundamental difference compared with a typical hydraulic automatic transmission, which uses an epicyclic (planetary) design, and a hydraulic torque converter. An automatic transmission that allows the driver to control the gear selection (such as shift paddles or "+/−" positions on the gear selector) is called a manumatic transmission, and is not considered a manual transmission. Some automatic transmissions are based on the mechanical build and internal design of a manual transmission but have added components (such as computer-controlled actuators and sensors) which automatically control the timing and speed of the gear shifts and clutch; this design is typically called an automated manual transmission (or sometimes a clutchless manual transmission).

Contemporary manual transmissions for cars typically use five or six forward gears ratios and one reverse gear; however, transmissions with between two and seven gears have been produced at times. Transmissions for trucks and other heavy equipment often have between eight and twenty-five gears, in order to keep the engine speed within the optimal power band for all typical road speeds. Operating such transmissions often uses the same pattern of shifter movement with a single or multiple switches to engage the next sequence of gears.