By Mike Unger
Driving a kart is a simple enough thing to do right? I mean you push on the accelerator, turn the steering wheel, and push on the brake pedal ~seems simple enough.
Well if you have been karting for just a day or a 1000 days you know it’s not that simple. One of the areas about driving a kart that seems to get the least attention is braking. I have worked with a number of drivers over the past few years and better braking techniques are something that we can all work on to become more successful racers. It is one of the things that separate the truly great racers from the average racers. This article will help you understand the various braking techniques, some drills to work one and give you some guidance on the physics behind it.
Let’s start off easy and look at the most simple case, braking in a straight line. Imagine you are at top speed (say 50mph) and yousimply need to come to a complete stop in the shortest distance possible. You are in a single speed kart, rear brakes only, with a standard hi stall clutch. It would seem like a simple thing to just hit the brakes as hard as you can, lock up the rear tires and slide to a stop. The obvious problem with this approach is that besides flat spotting your tires you will not stop in the shortest distance possible. This is due to the characteristics of friction between the road and your tires. Dynamic Coefficient of Friction (friction generated when sliding) is less than Static Coefficient of Friction (friction generated when there is no sliding between the tire and road). Because of this characteristic the shortest stopping distance will happen when the tires slow as fast as possible without locking up and sliding. Modern day automobiles make this easy on the driver as they all have anti lock brakes. You simply slam on the brakes, the car’s computer modulates the brake line pressure to keep the tires right on the edge of locking up throughout the braking maneuver and the car comes to a stop in the shortest distance possible. Of course karts don’t have such systems so driver skill is the difference between a good stop and a very good stop.
To begin to understand how we need to brake let’s first talk physics and energy. Kinetic energy is the energy of something that is in motion.
The basic equation for kinetic energy is: Kinetic Energy = mv2/2, where m is the mass of the kart, and V is the velocity of the kart.
The act of braking basically turns all of the Kinetic Energy into heat. All of the heat is generated by the brake pads rubbing against the brake rotor. Looking at the equation as the mass goes up the Kinetic energy goes up in a linear fashion. But as the speed goes up the energy goes up by a square of the velocity. Simply put the faster the vehicle is travelling, the amount of energy required to stop it goes up exponentially.
Why is it important to understand all of this equation stuff? Well if you understand the concept of the equation you can understand the most important part of how to stop in the most effective way. The goal is to turn all of the Kinetic Energy into Heat in the shortest time possible without sliding the tires. By knowing that the Kinetic Energy is a function of the square of the velocity you will realize that you will need to apply a larger brake force to the brake pedal at high speeds and decrease the pedal force proportionally as the speed of the kart slows down. Knowing this and applying it is key to maximum braking effectiveness.
One thing that makes braking so difficult in most karts is that you only have rear brakes. The reason why this is such a big deal is because when you start decelerating the weight on the rear of the kart will transfer forward. When this happens the amount of grip capacity of the rear tires drops. In simple terms, besides the fact that you need to compensate for the kinetic energy being related to the square of the velocity, as you brake harder the rear tires get lighter making it easier to lock them up. Anti lock brakes on karts would be a good thing to have huh?
So knowing all of that, let’s get back to the kart. As mentioned before in the simplest case you are travelling in a straight line at 50mph and need to stop as quickly as possible. The most effective braking technique will be to get the tire to the very edge of locking up as quickly as possible. Then as the weight transfers and the speed drops you will need to decrease the amount of force you are applying to the brake pedal to keep the tire right on the edge.
In technical terms the first part of the braking maneuver is called the initial apply. Getting this part done quickly is critical. The reason why it is so critical is because at the beginning of the braking maneuver at 50 mph you are travelling at 73 feet per second. Every 0.1 second you delay getting the tires to the maximum braking point you burn up 1.7 feet. We all know that missing a turn in point by 1.7 feet is a big deal so getting it right is important. The perfect initial apply with be a very quick, hard apply that will bring the tire right to the very edge of locking up as quickly as possible. It seems simple enough but it will take quite a bit of practice to get it right. After you have the initial apply down you will need to reduce the pedal force in proportional to the karts speed in order to get stopped in the shortest distance. Getting it right will require a significant amount of practice and a good consistent braking system on your kart.
I recommend this simple drill to help with the most simply case. For this drill you will need to have a track that has very little traffic on it or a very hard braking zone in it. Basically you just focus on braking in a straight line to a stop or to a very slow speed. If there is anyone at the track with you I highly recommend that you explain to them what you will be doing so they don’t run into you when you do it. It would also be good to choose a place on the track that is off the racing line. Pick a braking point on the track, a crack in the asphalt, a skid mark, or even a cone if available. Come up to speed and when your front tires cross that mark, hit the brakes and show down as fast as possible. Again a quick hard initial apply followed by progressively less pedal force as the kart slows. It will take a number of tries to get it right. When you do you will feel and hear the rear tires chirping, just barely locking up all the way through the stopping maneuver. The other thing you will notice is that you can stop much faster than you ever thought you could. With more practice you will learn to brake like that every time until it is instinctive.
But not so fast, you are not quite ready to set the track record yet. To truly go fast you need to learn the skill of trail braking. Trail braking is simply when you continue your braking maneuver into the turn. This technique is something that veterans already do and beginners struggle with. But one of the big differences between a fast driver and a slow driver is how well you can trail brake.
The reason why trail braking is so important is because it allows you to take your braking points even deeper because you use part of the corner to slow the kart down. The problem of course is that besides the modulation of the brakes that you have to do because of the weight is transferred off the rear tires and the rapid reduction of Kinetic Energy, when you turn the steering wheel you unload the inside rear tire. By turning the wheel your braking contact patch acting on the road is cut in half. You will have to really learn to modulate the brakes as you turn the steering wheel. The more you turn the steering wheel the less braking you can ask the tire to do. If you try to brake too much while turning you will spin. Brake too little and you miss the corner. But lucky for you the same basic techniques you learned while braking in the straight line applies in the case of trail braking. The trick now is you will need to learn to modulate the brake pedal as you turn the steering wheel.
For this drill I usually find a corner on the track that requires quite a bit of braking and is a fairly low speed turn. Approach thecorner as you normally would and have a friend mark with a cone or some other kind of marking device exactly where you hit the brakes. Now your job is to brake later than that point and work to carry the brakes all the way to the apex of the corner. Don’t worry about the proper line or making a good exit yet. This exercise is meant to give you more experience braking at the limit and turning at the same time. Once you learn to modulate the brake pedal as the velocity drops, weight transfers, and the steering wheel is turned you will be able to apply new skills to the track. This will become a powerful tool and help you lower your laptimes.
As you work through this exercise you will also come to realize you will be able to use trail braking to help make the kart turn. This is a very powerful skill to develop. Applying a little too much brake while turning will cause the kart to rotate into the corner more. In situations where you are fighting an understeering kart, or racing in the rain, advanced trail braking will be a very valuable asset to have. The catch is, like most things in life, it takes a considerable amount of practice to master this skill.
To practice this skill use the same corner you did in the original trail braking maneuver but this time use the steering less and use the brakes to rotate the kart into the corner. More brake force will rotate the kart into the corner. Less will straighten the kart out. Don’t even think of trying to do this until you master just normal trail braking. This final braking skill is the most difficult and the one that will take the most time to learn to do. But given enough time and hard work you will be able to do it. Just be ready for a few off track excursions on the road to enlightenment.
So there you have it. I suspect after you read this you’ll realize how much you have been taking braking for granted. It is a very important and powerful skill to develop. Use these drills to better your skills and ultimately better your laptimes. It will take some understanding of the physics involved and lots of work but when you figure it out it will be worth it.