Left-foot braking: Your mileage may vary | BimmerWorld’s James Clay

After years of hearing the benefits of left-foot braking, and some iterations in equipment allowing more complete adoption (sequential transmissions and, more recently, paddle-shift cars), I can tell you it’s been a journey.

In the early days with an H-pattern standard transmission, I struggled to find the benefit–the tires can only do so much work, and it’s easy to overload them when adding inputs (and work requirements).

I spent a tremendous amount of time left-foot braking street cars to calibrate that foot, more often used for on-/off-clutch inputs, into a useful tool. The results for me were a fail. Even in a car with a racing sequential where I used the left foot at times (especially to combat knockback on the brakes), it never showed an overall benefit in lap times for a single lap–or a session.

Then we got our first M4 GT4 with a DCT transmission. A factory car with tuning for shifts both up and down, a manual pedal box without a booster that I could wail on, and turbos that liked the throttle plate opened early so they were ready to make power when needed–the perfect foundation to make left-foot braking work.

Immediately I found (thanks to the non-boosted pedal) that the hardest part of adopting left-foot braking was where I put my left foot when I left the pits. If I had it near the brake in the first braking zone, that was where it remained and there was no thinking required for which foot I would use.

And surprisingly the biggest benefit I found (again, with the non-boosted brakes) is that my left foot was ready to turn the brakes ON–and interestingly, even though I was no longer rev-matching for the DCT transmission, my right foot while braking had too many years of programming to blip a throttle, which showed up as small variations in brake pressure.

The left foot was the hammer, and my right foot was too variable. I was also able to continue on this journey when I started driving the BMW M240i Racing with a boosted pedal, which allowed (and required) refinement with a more delicate pedal approach.

In this era, my braking became more consistent, my taps before braking for knockback were easier with less dancing on the pedals, and I started to experiment with the right amount of overlap to get the turbos ready mid-corner to optimize power out of the turns–all wins.

But after a year and change, I noticed the other side of the coin: the problems I was also causing.

I was prepositioned over the brake pedal while accelerating into the braking zone and deployed the left-foot hammer immediately–but I’m not driving a formula car, and the car wasn’t ready for the abrupt transitions.

There is value, even with a stiffly sprung race car, in time to transition the weight. And while this can be done with thoughtful application rate, there is also some value in a minimal pause time while all this is happening. (I know, time coasting is time lost, but it’s not that absolute.)

I had also worked on overlap (the way I came off the brake pedal in trail braking and when I came onto the throttle to spool the turbo), and it did help turn exit–at times. But the undesired side effect is, while cracking the throttle does start the turbo spool, it also moves you off the decel ramp in a typical clutch-type limited-slip and, worst (and most typical) case, onto the accel ramp, increasing diff lockup and affecting the mid-corner phase of the turn.

So your turbo is ready to make the power, but you’re waiting on an induced mild push to be able to fully apply it–again, in very small amounts. And all of these things, which added another input into the mix when the driver is giving bits of two pedals at once, were also hurting the tires, both immediately (a tire can show small effects of grip loss due to load for a corner or two until it cools back off) and over the span of a stint.

Then, an eye-opening moment came when Bill Auberlen joined our team and added his data to the pile for dissection. He’s not a left-foot braker. And once I saw that and started paying attention, I understood that very few elite drivers are, and not for the reasons above only.

Of significant concern when adding more throttle use, both deeper into the turns and earlier coming out of turns, is fuel use. This may not be a concern for most drivers not looking to stretch a stint another lap, but it’s a factor. And while working through the data, removing the left foot from braking (other than standard knockback tapping) wasn’t slower!

And through a year of going back and forth on foot use for both myself and some of my teammates, all under the watchful eye of our engineer, the clinching moment for me was when our engineer told me that I was losing out over a stint due to the tire energy expended by asking too much–0.1 or 0.2 a lap, so it wasn’t much, but I think very few drivers are in the habit of accepting any level of loss.

So where am I now? I can produce very similar lap times with left- or right-foot braking, and I have to make a conscious choice on which to use because I’m comfortable with either.

I know I’m slightly faster and make tires last longer (longer in the performance window–this isn’t a consumable tire wear concern) when I right-foot brake–and I do.

The left foot continues to handle knockback taps before every braking zone. And in some very rare instances, I still use left-foot braking on a very few specific braking zones because they are extremely high-speed, I’m busy for some reason in the car, and I want the confidence that when I pull the trigger and drop a foot to brake, the brake pedal will be squarely under it with no concerns of my foot slipping or not being able to hit the needed pressure for an intense application.