Left Foot Braking
Left foot braking is exactly as the name says. In case you need to stay on the throttle and brake at the same time you can use your left foot for braking.
Since the left foot is mostly used for quick, forceful stomps on the clutch most people almost fly into their windshield if they try left foot braking for their first time. It takes some practice getting used to left foot braking, because just as with your right foot you should be applying delicate braking pressure. People who are used to driving vehicles with automatic transmission are likely using their left foot for braking already.
If youd like to perform more advanced braking techniques with the left foot its important to first develop a feeling for the braking pressure. Normally, when using the right foot, if you bring your car to a full stop subconsciously you release braking pressure as the car slows down. Your subconscious is trained to do this for the right foot, but not for the left foot!
Learn braking hard, or preferably threshold braking, with your right foot first before moving onto learning left foot braking...
FERRARI ENZO PEDALS DESIGNED TO AID LEFT FOOT BRAKING
So why would anyone need to brake and throttle at the same time? Theres more than one advantage to left foot braking...
First of all youre decreasing the time to switch between the throttle and brake pedal. You can immediately get back on the throttle once the braking is complete. Of course left foot braking cant be performed if there is the need to shift down and use the clutch.
Secondly the effect of going off the throttle and on the brakes with the right foot upsets the cars balance. Releasing and applying them simultaneously with the right and left foot will result in improved stability and more smoothness for the transition.
Performing left foot braking while lightly remaining on the throttle results in better stability and handling. In spite of the little drag the brakes cause the weight shifts in a much more stable way. And with improved stability you go faster through corners.
With left foot braking you can modulate both pedals to be in more control of the weight transfer.
By controlling the weight transfer you can increase or decrease front or rear tire grip, which influences oversteering or understeering behavior. Especially effective in front-wheel-driven vehicles, simply because it's the best way to control the rear.
There are a lot more advantages for this braking technique. If youre going round a corner and got too soon on the throttle, then by applying a little left foot braking you can get the same result as releasing some of the throttle. As it keeps the engine pulling this is beneficial to your exit speed, especially for engines with a turbo.
In cars that feature a huge turbo, turbo-lag can become a problem when releasing the throttle. By staying on the throttle and keeping the engine up in the higher RPM range, the turbo wont be allowed to drop off boost completely and it will retain enough boost to minimize turbo-lag.