The engine�s power is fed to the rear wheels via a gearbox. This gearbox must have a minimum of four forward gears and a maximum of seven gears (although everyone opts for either six- or seven-speeds). A reverse gear must be fitted. The gearbox is connected to a differential � a mechanical device that determines how the power is split between the inner and outer wheels. Driveshafts take the power from the differential to the wheels. These principles are exactly as in almost every car in the world. But the detail is very different.
Although the system of cogs and shafts are like a conventional manual gearbox, the gears are selected not by a conventional mechanical linkage but by hydraulic pressure actuated by electronic control. Although the driver can change the gears, usually the gears are selected automatically, controlled by the electronic brain of the engine. This system saves time (electronically controlled shifts take less time than manual shifts), increases safety (the driver can have both hands on the wheel at all times), and helps the car aerodynamically (the cockpit can be narrower because it doesn�t have to include a gear lever). A very fast manual upchange using the old mechanical system used to take around 0.1 seconds, during which time the car would lose about 2 mph because of the high aerodynamic drag and engine compression of the car. The electronically controlled shifts take only around 0.02 seconds.
The differentials can be tuned to alter the handling characteristics of the car. These too are electro-hydraulically controlled and have sensors measuring the torque being fed to each driveshaft. The traction control system, which cuts the power when wheelspin is detected
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