What are the brakes for?

Mario Andretti once said he was amazed by how “drivers still think the brakes are for slowing the car down”. Clearly brakes play a part but, for a racing driver, the brakes are there to allow the car to reach an apex in the quickest possible time and achieving the highest possible apex speed. This is achieved by using the brakes to control the pitch and weight of the car – front to rear – as it enters a corner and in doing so alters the balance of grip from front to rear and vice-versa. If a driver can modify the balance of the car, this extracts the most amount of grip from each end of the vehicle, thus giving the driver the all-important lap time.

The key technique to extract the best performance from the brake pedal is not brake and then turn. Racing is all about blending these phases of a corner together in one seamless and almost imperceptible transition from entry to exit and drivers use a technique called “trail braking”. Trail braking is a term used to describe the technique of lightened, yet continued braking while turning into a corner. To trail brake is to blend braking and turning at the same time. It enables a driver to brake slightly later, but more importantly, manipulate the car’s mass, therefore changing the load on each axel to aid corner entry.
Trail braking is a difficult technique to get consistently right. It requires a lot of feel to ensure the driver getting the most out of all four tyres at corner entry, but when it is done well, it is fast, seconds a lap fast per corner fast.
Here’s how to trail brake:

  • Brake in a straight line at maximum force
  • Slightly before the turn in point begin to ease off the brakes
  • Begin to turn into the cornerAs you increase steering angle, reduce braking pressure
  • Use appropriate amount of braking to keep a well-balanced car through the corner entry phase

When trail brakeing, the driver is able to brake a few metres later than normal, but ensures the majority of the deceleration is done in a straight line. When approaching the turn-in point (tuft of grass, change of surface or other marker) begin to ease off the brakes. It’s important that this part of the process is smooth – begin to come off the brakes too quickly and you’ll unbalance the car. At the turn-in point, start to turn the car toward the apex. This is the point where trail braking begins, as you’re trailing the brakes past the turning area.

As the steering angle is increased to bring the car into the apex, the driver needs to continually release brake pressure. The more steering input, the less braking force the tyres are able to keep until the final 10-15% of brake pressure, where the driver will only be using the brakes to control the pitch of the car. This is the tricky part, where the car may rotate (oversteer) and a delicate touch is required. Just before the apex the driver should be completely off the brakes and the tyre’s grip will be wholly used for cornering, with no grip used for deceleration.

It should be said that it’s not necessary to trail brake into all corners. Trail braking is best suited to slow and medium corners where we want to ‘rotate’ the car before the apex to turn the car more and open up the exit, allowing us to get on the throttle earlier. In faster corners drivers will not trail brake as much and likely come off the brakes earlier (although probably still trail a little) so to avoid transferring too much grip to the front tyres and keeping the rear settled (which is what you want in the quick stuff).

The amount of trail braking needed for a specific corner isn’t set in stone. The driver needs to be dynamic in their approach as the difference in corners, setup, track temperature and so on, will affect the balance of the car and the amount of trail braking required. For this reason, trail braking is about feel and reacting to how the car moves once turned in. Finally this technique is used equally on front, four and rear wheel drive cars to good effect.

This technique is at odds with teachings for road driving as well as track day or racing schools. Why? When braking, load is taken off the rear axel and transferred to the front. This is fine when braking in a straight line, but when a driver introduces steering lock, the fronts will have lots of grip given the additional load, work significantly better, and turn the car well. Conversely the rear has had all the load taken away and is liable to rotate the car in a oversteer action due to having no load placed upon it. As a consequence, if a driver is not use to how the car will behave with a given input, spins are an inevitable result. The same is true of lift off oversteer. The transfer of load from the rear (on acceleration) to the front (when lifting off) with steering angle causes a loss of traction on the rear and rotates the car. So the safest way to drive is to brake and accelerate in a straight line and steer with no or neutral power.

Please don’t try this technique on the road. Even on a track please understand that it is highly likely you will end up facing the wrong way moving quickly to the scene of our own accident. I have spun learning this technique this many, many times, once causing a re-shell, new door, new gearbox, new wishbones, new track rods, new wing and so on. Search YouTube for “Silverstone Qualifying Prang 750 Motor Club Clio 182 Series”, I am in the blue car. I would strongly suggest anyone interested in trying it out book the Lancia Motor Club track day and use slow speed corners, building up speed slowly and carefully.

rthurbin

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