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Clutch control

Clutch control is the controlling of the speed of a manual transmission vehicle by partially engaging the clutch plate, using the clutch pedal instead of (or in conjunction with) the accelerator pedal. The purpose of a clutch is in part to allow such control; in particular, a clutch provides transfer of torque between shafts spinning at different speeds. In the extreme, clutch control is used in performance driving, such as starting from a dead stop with the engine producing maximum torque at high RPM.

With the clutch pedal completely pressed or a motorcycle's lever pulled entirely towards the driver, there is no direct link between the engine and the driveshaft, so no power can pass from the engine to the driveshaft and wheels. With the pedal entirely released, there is full contact between the engine and the driveshaft, via the clutch plate, which means that the engine can apply power directly to the driveshaft. However, it is possible to have the clutch plate partially engaged, allowing the clutch to slip. As a result, only a fraction of the power from the engine reaches the driveshaft, which is commonly known as half clutch.

There are benefits to the use of clutch control in specific circumstances:

When a car is in first gear, small variations in engine speed translate to large changes in acceleration and engine braking. However, with a combination of clutch control and careful use of engine speed, a much smoother ride can be achieved by allowing the clutch to slip. Variations in engine revs are not immediately translated into changes in drive shaft rotation speed, but rather the friction on the clutch plate allows the drive shaft to gradually equalize with the speed of the engine.

At a certain point while gently lifting the clutch, the car will begin to move as the clutch starts to slip, referred to as the biting point. Here, the accelerator pedal should be gently depressed to slowly increase the car's speed. Once the car reaches a suitable speed, the clutch can be fully engaged and speed can then be controlled either by varying the engine speed or by partially disengaging the clutch again if necessary.

This particular use of clutch control is frequently taught to learning drivers as a way to control acceleration when pulling away from a complete stop or when driving at very slow speeds while minimizing the chance of stalling the engine.

Creeping generally refers to moving slowly, and is generally analogous to a parking situation or very slow moving traffic. Creeping is usually done in either reverse or first gear, like when reversing out of a parking space or pulling into a driveway. While moving at low speeds like these, it is often not necessary to use the accelerator pedal as an engine's idle speed should provide enough torque to do so, given a driver is careful enough with the clutch pedal. Revving the engine higher than necessary while moving at low speeds and the clutch not fully engaged can cause damage to the system due to heat caused by friction on the clutch material, reducing its usable lifespan. This is mitigated in most motorcycles by the use of a wet clutch.

When pulling away on an uphill slope, the chance of stalling the engine is greater, and so it can be beneficial to engage the clutch more slowly than normal while revving higher than normal.

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