Left-foot braking

Left-foot braking is the technique of using the left foot to operate the brake pedal in an automobile, leaving the right foot dedicated to the throttle 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.

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, and can also be used to control load transfer.

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.

Racing and rallying
Karts, many open wheelers, and some modern road cars (cars that are mounted with automatic transmission or semi-automatic transmission which is the Formula One style gear box), have no foot-operated clutch, and so allow the driver to use their 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, potentially causing trailing-throttle oversteer, 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 reduce understeer.

In rallying left-foot braking is very beneficial, especially to front-wheel drive vehicles. It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake (retarding actually, to reduce traction, rarely fully locking - best considered a misapplication), 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. It is not as necessary to use this technique with Rear-wheel drive and All wheel drive rally vehicles because they can be easily turned rapidly by using excess power to the wheels and the use of opposite lock steering, however the technique is still beneficial when the driver needs to decelerate and slide at the same time. In rear wheel drive, left foot braking can be used when the car is at opposite lock and about to spin. Using throttle and brake will lock the front tires but not the rears, thus giving the rears more traction and bringing the front end around.

Swedish rally legends Erik Carlsson and Stig Blomqvist are considered to be the inventors of left-foot braking, developing it while driving for the SAAB works team in the 1960s and '70s.

When left foot braking is used to apply the brake and the throttle at the same time it is very hard on the car, causing extra wear on the transmission and brakes in particular.

This technique should not be confused with heel-and-toe, which is another driving technique.

Road use
Many commentators advise against the use of left-foot braking while driving on public roads.

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 and potentially dangerous acceleration.

Most manufacturers of cars with automatic transmissions provide the car with a rest for the driver's left foot so the right foot may be used exclusively for throttle and braking.

Also, when the left foot is often used for depressing the clutch pedal this generally requires more force than operating the brake. A driver accustomed to applying this amount of force may unexpectedly slow down to an unsafe speed when attempting to use the left-foot braking technique.

In addition, many modern vehicles use a "Drive By Wire" or Electronic throttle control system instead of the traditional mechanical throttle linkage. These systems have a safety interlock that prevents left foot braking. The car's ECU can detect when both pedals are pressed simultaneously and will immediately cut the engine power for safety reasons.

In vehicles equipped with a hydraulic braking system applying throttle with the gearbox in neutral can provide more pressure to the brakes, effectively increasing their performance. This increase in hydraulic pressure must be taken in consideration when estimating the braking force necessary.

Maneuvering with automatic transmission
However, some commentators do recommend left-foot braking as routine practice when driving vehicles fitted with an automatic transmission, when manoeuvring at low speeds. (See, for example, The Daily Telegraph columnist "Honest John").

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 absence of a clutch on a vehicle with automatic transmission means that there is no such safety override, unless the driver has a foot poised over the brake pedal.

Critics of the technique suggest that it can cause confusion when switching to or from a vehicle with a manual transmission, and that it is difficult to achieve the necessary sensitivity to brake smoothly when your left foot is used to operating a clutch pedal.