Left Foot Braking
Left foot braking, a phrase oft spoken in hushed tones usually while recounting the skill of legendary drivers in motorsport. But what actually is it and why is it seen as such a big deal?
Left foot braking as we are discussing here is mainly relevant to a manual car (cars with paddle shift are normally left foot braked regardless of situation). It is the technique of using your left foot to actuate the brakes of your car usually mid corner or where a downshift (where your left foot would be needed to use the clutch) is not necessary. So what’s the point in doing this? Why would you want to use the brakes mid corner? The main situation where this is useful is when the car is understeering. When a car is understeering a transfer of weight towards the front of the car is favourable to increase the grip that the front wheels have along with a slight reduction in speed. Both of these things will stop the understeer and allow the driver to continue to take the corner on their desired line.
The conventional way to deal with understeer, at least to begin with for new drivers, is by lifting the throttle. This is usually sufficient to bring the car back into line and allow the driver to exit the corner cleanly. However lifting the throttle can have some unwanted side effects, firstly the reduction in speed can be difficult to control. The loss of speed can in some cases be quite sudden (high compression naturally aspirated engines especially can suffer quite extreme compression braking) and once you’ve lifted from the throttle if you don’t achieve sufficient deceleration there’s no way to increase the speed reduction further. Another side effect of using a lift to deal with understeer, especially in a car that’s aggressively set up with a loose rear, can be that the car then responds too much to the lift resulting in a snap into oversteer. This of course is undesirable, not only as it can be difficult to control or catch, but also because it results in a greater loss of time through the corner as the driver regains control of the car.
This is where left foot braking comes in. Left foot braking gives the driver far more control over the deceleration of the car as the brakes can be modulated to precisely the right amount without causing sudden changes in the attitude of the car. This results in far smoother driving, which is usually accompanied by lower lap times.
But that’s not all, there are also other benefits to left foot braking as well. In a turbocharged car, left foot braking allows the driver to get on the throttle earlier in the corner (or not lift to counter understeer) meaning that boost can build and be maintained ready for the corner exit. This is the main reason that historically left foot braking has been largely associated with rally drivers, especially in the group B era, where maintaining boost pressure with large laggy turbochargers was paramount in order to go fast.
There are additional benefits to staying on the throttle in other types of racecar as well. It is important to remember the effect of differentials within racecars. In order to lock up a limited slip differential it must have torque applied to it. This means that the driver must apply the throttle achieve lock, in some situations it is desirable to maintain the lock within the diff mid corner while dealing with understeer, usually to aid traction and maintain stability.
The best way to try or improve on your left foot braking technique is by attending track days and doing it in a safe environment. Experimentation is the best way to learn!