Manual

A manual transmission (also known as a stick shift or just stick, straight drive, or standard transmission) is a type of transmission used in automotive applications. Manual transmissions often feature a driver-operated clutch and a movable gear selector. more...

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Most automobile manual transmissions allow the driver to select any gear at any time, but some, such as those commonly mounted on motorcycles and some types of racing cars, only allow the driver to select the next-highest or next-lowest gear ratio. This second type of transmission is sometimes called a sequential manual transmission.

Manual transmissions are characterized by gear ratios that are selectable by engaging pairs of gears inside the transmission. Conversely, most automatic transmissions feature epicyclic (planetary) gearing controlled by brake bands and/or clutch packs to select gear ratio. Automatic transmissions that allow the driver to manually select the current gear are called semi-automatic transmissions.

Contemporary automotive manual transmissions are generally available with four to six forward gears and one reverse gear, although manual transmissions have been built with as few as two and as many as eight gears. Semi-trucks have at least 13 gears and as many as 24. Some manuals are referred to by the number of forward gears they offer (e.g., 5-speed) as a way of distinguishing between automatic or other available manual transmissions. Similarly, a 5-speed automatic transmission is referred to as a 5-speed automatic.

Other types of transmission in mainstream automotive use are the automatic transmission, semi-automatic transmission, and the continuously variable transmission.

Manual transmissions come in two basic types: simple Non-synchronous systems, where gears are spinning freely and their relative speeds must be synchronized by the operator to avoid noisy and damaging \"clashing\" and \"grinding\" when trying to mesh the rotating teeth; and synchronized systems, which eliminate this necessity while changing gears.

Unsynchronized transmission

The earliest vehicle transmissions could be shifted, with multiple gear ratios available to the operator, and even had reverse. However, the gears were engaged by sliding mechanisms or simple clutches, which required a lot of careful timing and throttle manipulation when shifting, so that the gears would be spinning at roughly the same speed when engaged; otherwise, the teeth would refuse to mesh.

When upshifting, the speed of the gear driven by the engine had to drop to match the speed of the next gear; as this happened naturally when the clutch was depressed or disengaged, it was just a matter of skill and experience to hear and feel when the gears managed to mesh. However, when downshifting, the gear driven by the engine had to be sped up to mesh with the output gear, requiring letting the clutch up (engagement) for the engine to speed up the gears. Double declutching, that is, shifting once to neutral to speed up the gears and again to the lower gear, is sometimes needed. In fact, such transmissions are often easier to shift without using the clutch at all. When using this method, the driver has to time the shift with relative precision to avoid grinding the gears. The clutch, in these cases, is only used for starting from a standstill. This procedure is common in racing vehicles and most production motorcycles.

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