All About Braking

Summary:

A common misconception about brakes is that their only function is to stop a vehicle, or slow it down. While that may be their main function, they have more functions in the racing world. We will go over the different types of braking used in professional environments, covering their purposes and how they are performed.

ABS vs NO ABS

Modern cars are equipped with a live-saving driver-assistance tool known as ABS (Anti-lock Braking System). Why is this so important for everyday use? In older cars that lack ABS, braking at 100% pressure will cause the brakes to lock up the front wheels, causing the front tires to lose grip, resulting in the car sliding, not being able to slow down as fast as possible. In addition to the grip being lost in the front, the driver is unable to steer the vehicle when the front wheels are locked. As a result of this locking phenomenon, people have gotten in many accidents in regular traffic and in racing environments. ABS’s job is to allow the driver to brake at full pressure by automatically adjusting the pressure to prevent lockups (this is why they will teach you not to slam on the brakes, but to “pump” the brakes in driving school; they are assuming the lack of ABS). Luckily, in the last 20 years, ABS has become standard in all production vehicles, however some race cars do not utilize ABS.

ABS, as great of a tool as it is, is not without its drawbacks. In regular street driving, it is a must-have and it wouldn’t make any sense to not use it. On the race track however, ABS can actually hold drivers back. New racers should always learn how to drive in a car that does not have ABS. This teaches them a high level of brake control, the most important being threshold braking (making use of 100% of the tire’s grip to slow down the car), which is done only by knowing where the brakes will lock, and braking with as much pressure as possible without reaching that point, consistently. Racers who learn to drive in a car with ABS and become proficient at braking will brake well, but they will be relying on the car’s systems to drive them, rather than them truly driving the car. A driver who has mastered racing without ABS will out-brake a driver with average braking skills utilizing ABS.

Using the Brakes for Weight Transfer

Remember when I said that stopping and slowing down is not the only function that brakes serve? The other function that I was talking about was weight transfer. Racing is all about balance, and mastery over shifting the weight of your car will set you in a league above the rest. Let’s dive into what is happening to the car’s weight when we brake and accelerate, and how to exploit it to make you faster on the track.

Have you ever seen a car when the driver slams on the brakes? You will notice that the front of the car dips down, and if you are the one slamming on the brakes, you will feel yourself being pushed forward quite hard, depending on how sudden and how much force you are applying (negative g-force). What you are seeing is the brakes doing what they were designed to do: converting kinetic energy into heat. This process of killing speed with friction causes the center of gravity to shift heavily to the front. If you have ever seen a car under heavy acceleration, you will notice that the car “squats” down, because the weight of the car is being transferred over the rear wheels. If you are the one doing the accelerating, you will feel like you are being pushed back in your seat (positive g-force). When you are first learning how to race, you may try to brake “safely”, by braking hard before a turn, then releasing the brakes fully before turning in. This 100%-0% before turn-in will only take you so far. To take your pace to the next level, you will need to learn a technique called trail-braking. Trail-braking is the exploitation of the weight transfer caused by hard braking to allow the driver to turn in sharper. When all of that weight is shifted to the front, the front tires have the most grip, and the rear of the car becomes lighter, making it more nimble. So let’s look at two drivers, one who is braking “safely”, and one who is trail-braking properly. The driver who brakes “safely”, approaches a tight right-hand corner shaped like a parabola: a hairpin turn. He/she brakes hard, slowing them down just enough to enter the corner. They stay at maximum braking pressure until they reach the turn-in point, and then they completely let go of the brakes. They make the turn safely, but their weight transfer was aggressive and not as balanced as it should have been. The weight was all on the front, then it very suddenly returned to the middle, and if the driver instantly got on the throttle, it went immediately from the front to the rear. This driver would probably be feeling something called understeer, a phenomenon that occurs when the front tires are not able grip enough, or the rear tires are gripping too much. Understeering not only will slow you down when racing, but it will put excess wear on the tires; when cornering, the weight is shifted to the outside tires. Now let’s take a look at the other driver. He/she brakes hard approaching the hairpin, but when they reach the turn-in zone, they stay on the brakes. As soon as they begin the motion of turning in, they slowly release the brakes until 0%. What this is doing is allowing the car to make a sharper yaw movement, because it has more grip in the front and less grip in the rear. This driver may be experiencing oversteer, a phenomenon that occurs when the rear tires lose grip and the car starts to skid. In the ideal situation, however, this driver was able to get through the turn much smoother, utilizing all possible grip in their tires, avoiding understeer and taking less time to complete the turn than the driver who did not trail-brake. Trail-braking is applicable in almost every type of turn, and should be practiced until it becomes instinct for the driver to stay on the brakes while turning in.

I mentioned earlier that when you are understeering you have to make adjustments to avoid crashing or losing too much time in a corner. One of the most commonly used methods of adjustment is known as left-foot braking. Left-foot braking is exactly what it sounds like: using your left foot to brake rather than your right foot. Knowing how the brakes affect the transfer of the car’s weight, a driver will use this technique to make fine adjustments to their moves: if they start to understeer, they may lightly brake with their left foot, not to slow the car down, but for the sole purpose of getting more grip on the front tires to carry them through the turn without going too wide through that turn. Fine weight transfers are not the only use for left-foot braking, though. In cars that do not have a clutch, many drivers dedicate their left foot to the brake so that their right foot never has to leave the throttle. Driving like this eliminates the milliseconds it takes for a driver to pivot their foot from the gas to the brakes. In cars with a clutch, left foot braking is a bit more uncommon, but is still used when there is no need to downshift while braking.

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