Left-foot braking
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Left-foot braking is the technique of using the left foot to operate the brake pedal in a car, leaving the right foot dedicated to the accelerator pedal. It contrasts with the normal practice of the left foot operating the clutch pedal, and the right foot operating the brake and accelerator pedals. It is most commonly used in auto racing, but is also used by some drivers for use with an automatic transmission, as the left foot is not needed to operate a clutch pedal. The most significant consequence is that the driver can operate both the accelerator and brake at once, creating the potential for spins, while not allowing the clutch and brake to be used together. It is generally not recommended practice and can be dangerous.
At its most basic purpose, left-foot braking can be used to decrease the time spent between the right foot moving between the brake and throttle pedals. It can also be used to control load transfer.
Racing and Rallying
Karts, many formula cars, and some modern road cars (such as the Enzo Ferrari), have no foot-operated clutch, and so allow the driver to use his left foot to brake.One common race situation that requires left-foot braking is when a racer is cornering under power. If the driver doesn't want to lift off the throttle, and potentially cause a trailing-throttle oversteer situation, left-foot braking can induce a mild oversteer situation, and help the car "tuck," or turn-in better. Mild left-foot braking can also help cure an understeer situation.
In rallying it applies primarily to front wheel drive vehicles. It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake, which is set up to apply a significant pressure bias to the rear brakes. The vehicle is balanced using engine power by use of the accelerator pedal, operated by the right foot. The left foot is thus brought into play to operate the brake. Rear wheel drive rally vehicles do not use this technique because they can be much more easily turned rapidly by using excess power to the wheels and the use of opposite lock steering.
This technique should not be confused with Heel-and-Toe, another driving technique.
Left-foot braking with automatic transmission
This practice is not recommended for drivers of road cars. The technique generally encouraged is for the driver to use the right foot for both acceleration and braking. The primary reason for this is that there is never any situation in a car with an automatic transmission where it is necessary to apply both brake and throttle at the same time. Using one foot for both makes certain that the driver will only be operating one pedal.
Additionally, in emergency braking situations, it is common for the driver to extend both legs in a panic reaction. If the right foot is on the throttle, this will cause unwanted acceleration.
For this reason, most manufacturers of cars with automatic transmissions will provide the car with a "dead pedal" (that is, a fixed, pedal-like rest) for the left foot. Which is also used to keep the driver at optimum seating position by providing somewhere to push in order to mantain properly seated.
Using the left foot for braking can also cause confusion when switching to or from a vehicle with a manual transmission because of the differing roles of the left foot. [link]
In spite of this, some commentators recommend left-foot braking as routine practice when driving vehicles fitted with an automatic transmission, particularly when maneuvering at low speeds. (See, for example, [HonestJohn])
Proponents of the technique note that in low-speed manoeuvres, a driver of a vehicle with a manual transmission will usually keep a foot poised over the clutch pedal, ready to disengage power when the vehicle nears an obstacle. This means that disengagement is also possible in the event of malfunction such as an engine surge.
However, the technique is of little value in such situations since, during low speed maneuvers, the right foot would not be necessary to control the throttle. This is because of the tendency of the car to move slowly forward (when in "Drive") or backwards (when in "Reverse") due to the idling of the engine.
Decline of Left Foot Braking
Many modern vehicles use a "Drive By Wire" or Electronic throttle control system instead of the traditional mechanical throttle linkage. These systems do not allow for left foot braking. As the throttle is connected to the car's ECU, it can detect when both pedals are pressed simultaneously and will immediately cut the engine power. This is in case of a malfunction in the throttle body or a stuck pedal. An example is all modern Volkswagen and Audi Group vehicles.
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