Biting points

Race clutch design and manufacture remains one of the most challenging fields in motorsport engineering, as we discovered when we engaged with some of the leading companies in the industry

- GEMMA HATTON

Whenever we sit in our road cars we are faced with two large dials displaying the vehicle’s speed and the engine speed (or the revs). Usually, unless you are trying to prove a point to the car next to you, or are on a race track, we very rarely accelerate the needle into the red zone near the rev limiter. This is because, despite internal combustion engines having a large range of operating speeds, there is only a very narrow window in which the engine can operate at its highest efficiency, where it is achieving the maximum output power for the minimum amount of fuel (brake specific fuel consumption, or BSFC).

Therefore, a transmission is used to effectively vary the speed of the driven wheels, to ensure that the engine is always operating within that efficiency band as the vehicle accelerates or decelerates. So when you accelerate, you are demanding more torque from the engine so the revs increase up to a point where you change to a higher gear and the revs drop back down before gradually increasing up through the rev range once again.

In a manual transmission, to enable a smooth transition between the gear changes, the flow of torque from the engine to the transmission has to be disconnected. Of course, it is not practical to turn the engine off every time you want to make a gear change. Therefore, a clutch is used to transfer the torque from the powerplant to the gearbox, and this can also be used to disconnect the engine from the gearbox during gear changes without having to turn off the engine.