Left foot braking is a pretty simple driving technique that you can use to help control front and all wheel drive cars through turns. It’s useful for a few reasons:
I would say the most important reason is to control the car’s balance. When you brake, the weight of the car shifts towards the front wheels. Purposely shifting the weight forward in a turn will give the front wheels some extra traction to dig the car out of the exit. Applying the brake against the throttle allows you to get the proper weight shift without over-braking and slowing the car too much.
The second reason that left foot braking is faster for front wheel drive cars is because it helps the differential. It’s easy for a car to lift its inside front wheel while trying to accelerate out of a turn. Reduced resistance on the lifted wheel will cause the differential to send more power to it which generally results in your engine power doing a one wheel burnout if you’re really trying to drive fast. Left foot braking prevents the lifted inside wheel from spinning too much so a higher percentage of the engine power goes to the outside front wheel to pull you out of the corner.
Chris Harris demonstrates the technique and talks about these benefits in this vintage AutoCar video:
The third reason that left foot braking is faster has more to do with race driving. When using both feet, you can switch between braking and throttle instantaneously. If you only use one foot, the car will have to coast for a split second while you switch pedals. This is the left foot braking excerpt from the Basic Rally Techniques with Colin McRae video where he talks about the racing application of left foot braking.
The last benefit to left foot braking is brake bias control. We all know that a gratuitous yank on the hand brake will lock up the rear wheels of a car and cause it to do wild spins. The problem is that the hand brake is more or less an on/off wheel lock switch and going into an uncontrolled spin is generally not the best way to lay down a fast lap time. Left foot braking allows you to have a rear brake bias with a lot of control and modulation. If you drag the brakes against the engine in a front wheel drive car, the engine power is still trying to turn the front wheels but not so in the rear. That means you will see a greater wheel speed reduction on the rear axle than on the front even though the car has more powerful front brakes. In addition to all of the other benefits we’ve talked about, left foot braking will give you a bit of controlled slip from the rear axle due to this brake bias effect. It’s less prominent in a high grip road racing car, but this controlled rear axle slide is a key technique for rally driving. Rally cars are sometimes set up with a rear brake bias to help initiate inertia drifts and to exaggerate the effects of left foot braking.
As with any other driving technique, be careful when training yourself to left foot brake. Don’t be an idiot and try to do it in traffic. You will have to develop a whole new level of sensitivity and coordination in your left foot. It’s also important that you understand that no single technique will turn you into a superstar race driver. Left foot braking is an additional tool to add to an extensive skill set and a fundamental understanding of balance and tire management (also known as physics) if you want to drive fast. Be smart so that you can drive safe. Then you can be good by practicing techniques. Once you’re good at techniques, you can put it all together to be fast.
Sources: AutoCar and nolanbowling on YouTube