Trail braking is one of the more misunderstood techniques in motorsport so in this lesson I will be talking a little bit about what trail braking is, but also importantly, what it isn’t. Plus, I’ll go over some training techniques to help you on your way to becoming a corner entry expert.
What is Trail Braking?
In basic terms, trail braking happens any time you decelerate a vehicle past the point of turn-in. Interestingly, the only reason we even have the term is that traditionally many drivers thought straight line only braking was the way to go. Continuing to brake into a turn was considered a special technique that may, or may not, be faster. We’ve come a long way since then however, and although some may still argue over the specifics of when and how trail braking should be done, it’s generally understood that learning it is required if you wish to have competitive times.
In basic terms, trail braking happens any time you decelerate a vehicle past the point of turn-in. Interestingly, the only reason we even have the term is that traditionally many drivers thought straight line only braking was the way to go. Continuing to brake into a turn was considered a special technique that may, or may not, be faster. We’ve come a long way since then however, and although some may still argue over the specifics of when and how trail braking should be done, it’s generally understood that learning it is required if you wish to have competitive times.
So let’s first talk a little about corner entry and how trail braking fits in. The science of optimizing a vehicle’s path around a race track is called line theory, and using just a few line theory principles we can understand how to optimize our corner entry. Based on its grip vs acceleration potential, every vehicle will have an optimum speed and angle it should be at as it passes the apex. Any faster or slower and the corner exit time will be compromised. During corner entry then, the goal is to reach this exact apex in the shortest time possible. To accomplish this, the vehicle should travel on a path of consistently reducing radius from the point it turns in until it reaches this apex. This makes the ideal corner entry line look like the beginning of an Euler (sounds like oiler) spiral. In the image below, you can see an Euler spiral laid over a corner showing the entry line. To see this live, as well as a comparison to other types of corner entries, check out this linked video.
In order to drive at the limit along this corner entry path, the vehicle will need a consistent increase in steering angle as well as a steady reduction in speed. If you are familiar with the concept of the traction circle, you’ll know that the increase in steering angle will also require a proportionate reduction in braking. In other words, you will need to “trail” off the brakes.
Trail Braking or Deceleration to the Apex?
I really don’t like the term "trail braking” very much however. I think it can lead to confusion because although you should ideally decelerate all the way to the apex during corner entry, this doesn’t necessarily mean you should use the brakes the entire way. Induced drag on the tires from slip angle as well as engine braking and aerodynamic drag are all already acting on the vehicle to slow it down. Depending on the car and corner, you won’t always need to continue using brakes in the final part of corner entry to achieve the proper deceleration rate. In fact, aerodynamic drag can be so powerful in fast corners sometimes that you might even need to use moderate throttle so that you don’t decelerate too quickly!
I really don’t like the term "trail braking” very much however. I think it can lead to confusion because although you should ideally decelerate all the way to the apex during corner entry, this doesn’t necessarily mean you should use the brakes the entire way. Induced drag on the tires from slip angle as well as engine braking and aerodynamic drag are all already acting on the vehicle to slow it down. Depending on the car and corner, you won’t always need to continue using brakes in the final part of corner entry to achieve the proper deceleration rate. In fact, aerodynamic drag can be so powerful in fast corners sometimes that you might even need to use moderate throttle so that you don’t decelerate too quickly!
Traction circle showing combined braking and turning at the limit. Additionally, although we’ve just learned that an ideal trail braking entry doesn’t necessarily end with actual braking, it doesn’t always begin with braking either. A typical corner entry will often require straight-line braking first before proceeding to steadily trail the brakes into a spiral shaped entry. But what would happen if the entry speed were lower and you reached the turn-in point before you needed to start braking? In this case, the Euler spiral shaped entry line would be exactly the same, but the vehicle would turn in at full throttle before switching directly to combined braking and turning at the needed point, part way into the spiral. The vehicle would then continue decelerating to the apex as usual from that point on.
Putting these two principles together, consider a high-speed corner where only a brief throttle lift was needed. The shape of the ideal entry line would again remain the same, but the deceleration forces to drop that small amount of speed near the apex all came from drag forces when you lifted the throttle. Even though you never touched the brakes, you are still following the same principles that make “trail braking” the ideal corner entry technique.
Putting these two principles together, consider a high-speed corner where only a brief throttle lift was needed. The shape of the ideal entry line would again remain the same, but the deceleration forces to drop that small amount of speed near the apex all came from drag forces when you lifted the throttle. Even though you never touched the brakes, you are still following the same principles that make “trail braking” the ideal corner entry technique.
G-G Diagram Trail Braking Misconceptions
So now that we’ve looked at what trail braking is, let’s look at a few things that it’s not. You often hear that you can tell how good at trail braking someone is by looking at how rounded their traction circle (G-G diagram) readout is as they transition from braking to turning. While being able to keep a vehicle at the edge of the traction circle does indicate good car control abilities, it doesn’t necessarily indicate a good corner entry. I’ve worked with many drivers who had a great looking traction circle readout, but were losing time during entry and were not able to figure out why. For some examples of how this can happen, check out the linked video. In the video, I demonstrate three different types of lines through a corner. Although I always kept the car at the very edge of the traction circle as I transition from brakes to turning, the times produced were very different. While learning to keep the car at the edge of the traction circle is an essential skill, to find that last bit of time, you also have to learn to be at the right place on the circle, at the right time.
So now that we’ve looked at what trail braking is, let’s look at a few things that it’s not. You often hear that you can tell how good at trail braking someone is by looking at how rounded their traction circle (G-G diagram) readout is as they transition from braking to turning. While being able to keep a vehicle at the edge of the traction circle does indicate good car control abilities, it doesn’t necessarily indicate a good corner entry. I’ve worked with many drivers who had a great looking traction circle readout, but were losing time during entry and were not able to figure out why. For some examples of how this can happen, check out the linked video. In the video, I demonstrate three different types of lines through a corner. Although I always kept the car at the very edge of the traction circle as I transition from brakes to turning, the times produced were very different. While learning to keep the car at the edge of the traction circle is an essential skill, to find that last bit of time, you also have to learn to be at the right place on the circle, at the right time.
You also often hear that the reason for trail braking is that the forward load transfer from braking helps a car turn better. In actuality though, due to the effects of load sensitivity, forward load transfer actually reduces a vehicle’s ability to turn. All four tires are working together to change a car’s direction, so the more evenly loaded they are, the more total force they can produce. As an example, if you raise a vehicle’s ride height, you will raise its center of gravity. A higher center of gravity will cause it to experience greater load transfer during corner entry, and because of load sensitivity, this will actually make it change directions slower. Load transfer is more related to car design and setup however. It doesn’t affect the ideal corner entry driving technique. For instance, imagine if we built a special race track with elevated platforms for the tires so the car’s chassis could hang down in between and allow the vehicle’s center of gravity to be even with the contact patches. This car wouldn’t experience any load transfer at all as it sped around the track. Although this would be quite a unique sight to see, the same corner entry technique of an Euler spiral shaped path with a steady reduction in speed to the apex would still be the ideal strategy.
Learning to Trail Brake
When first learning to trail brake, I recommend starting with a straightforward approach to initially just get used to the basic idea. During corner entry, just try to focus on steadily increasing steering while also steadily releasing the brakes. An old visualization trick to help with this is to imagine one end of a string tied to the bottom of the steering wheel and the other tied to your toe. As you turn the steering wheel more, the string would begin to pull your foot off the brake.
It’s a good idea to spend some time to make sure you can accomplish this part, because once you pick up the pace, the difficulty can ramp up quickly. Depending on the vehicle and corner, the car control challenge alone of driving at the limit during trail braking ranges from hard to seemingly impossible. As I mentioned earlier though, even once you do learn to ride the edge of the traction circle, there are still plenty of ways to lose time while trail braking. That is because the goals of corner entry are a bit of a paradox. While an ideal corner entry maximizes deceleration, if you actually concentrate on doing this, you could very well over-slow the corner without even realizing it.
When first learning to trail brake, I recommend starting with a straightforward approach to initially just get used to the basic idea. During corner entry, just try to focus on steadily increasing steering while also steadily releasing the brakes. An old visualization trick to help with this is to imagine one end of a string tied to the bottom of the steering wheel and the other tied to your toe. As you turn the steering wheel more, the string would begin to pull your foot off the brake.
It’s a good idea to spend some time to make sure you can accomplish this part, because once you pick up the pace, the difficulty can ramp up quickly. Depending on the vehicle and corner, the car control challenge alone of driving at the limit during trail braking ranges from hard to seemingly impossible. As I mentioned earlier though, even once you do learn to ride the edge of the traction circle, there are still plenty of ways to lose time while trail braking. That is because the goals of corner entry are a bit of a paradox. While an ideal corner entry maximizes deceleration, if you actually concentrate on doing this, you could very well over-slow the corner without even realizing it.
The Corner Entry Paradox – Deceleration vs Time
One of the very first visualization exercises I like to go through with a driver helps to explain the corner entry paradox. Imagine you are in a braking challenge where you cross a start line at any speed you wish and then try to stop with the front tires in a small strip 50 meters away as quickly as possible. If the tires go past the strip, you lose. Following line theory principles, we can understand that the ideal result would come from crossing the start line at the exact speed that would allow us to threshold brake for the entire 50 meters landing the front tires right on the strip.
One of the very first visualization exercises I like to go through with a driver helps to explain the corner entry paradox. Imagine you are in a braking challenge where you cross a start line at any speed you wish and then try to stop with the front tires in a small strip 50 meters away as quickly as possible. If the tires go past the strip, you lose. Following line theory principles, we can understand that the ideal result would come from crossing the start line at the exact speed that would allow us to threshold brake for the entire 50 meters landing the front tires right on the strip.
While it’s relatively easy to understand on paper why this would be ideal, actually accomplishing it would be nearly impossible. Going slightly too fast across the start line or having any imperfection in braking technique would cause the car to go past the strip. A human needs a more realistic approach and, as a test, I actually did this challenge with several drivers. For the test, I had each driver try two different strategies. First, I had the driver attempt the theoretical ideal where they would try to maximize their braking from the start line to the strip. After this, I would then have them instead focus on simply trying to reach the strip as quickly as possible. Almost without fail, having the driver focus not on braking, but on reaching the strip as quickly as possible, resulted in lower elapsed times and much fewer faults. When a driver tried to keep their focus on maximizing their braking, they would often have to release additional brake pressure near the end so they didn’t come up short on the target. Either that or they would try to brake too deep and end up going past the strip.
This result makes sense because, in the more successful strategy, drivers were focusing on the goal that truly matters - minimizing their time. If you remember from the beginning of the article, this is also the true goal we have for corner entry, which is to minimize the time it takes to reach the ideal apex. In our braking challenge, as well as corner entry, maximizing deceleration is just a side effect of doing this well, but it’s not the actual goal. Of course, a typical corner entry with trail braking is a good bit more difficult than just straight line braking, but the principles are the same. Learning to focus on having your vehicle reach an ideal apex as quickly as possible in time is a key element to a proper corner entry.
This shifting of focus to how your vehicle is actually moving around the track is also an important step in a driver’s journey. In the beginning, as you are learning the basic mechanics, visualization techniques such as the string, which primarily focuses on memorized control patterns, can be helpful. Eventually however, you will need to move beyond this if you wish to continue progressing. I have seen countless drivers who hit a skill plateau, as they try to essentially memorize an ever more complex sequence of control inputs around a race track, in an attempt to find lap time. Not only is this approach quite limiting, speaking from experience, it’s also not very fun.
What is not only a lot more fun, but also quite amazing to see for most drivers, is when someone can jump into an unfamiliar car at a new track and quickly start laying down competitive laps. Their data might show picture perfect Euler spiral entries with ideal steering and brake traces, but none of this was planned or memorized. Instead, through proper training, they have learned to focus on the true goals as they drive, and that was simply the result.
I hope you enjoyed this lesson and if you have any questions, please use the comments section below. Up next, we’ll look take a deeper look at the physics of trail braking. If you are interested in a complete guide to the physics of racing, we also offer The Science of Speed book series, available through our bookstore or at popular retailers such as Amazon.
This shifting of focus to how your vehicle is actually moving around the track is also an important step in a driver’s journey. In the beginning, as you are learning the basic mechanics, visualization techniques such as the string, which primarily focuses on memorized control patterns, can be helpful. Eventually however, you will need to move beyond this if you wish to continue progressing. I have seen countless drivers who hit a skill plateau, as they try to essentially memorize an ever more complex sequence of control inputs around a race track, in an attempt to find lap time. Not only is this approach quite limiting, speaking from experience, it’s also not very fun.
What is not only a lot more fun, but also quite amazing to see for most drivers, is when someone can jump into an unfamiliar car at a new track and quickly start laying down competitive laps. Their data might show picture perfect Euler spiral entries with ideal steering and brake traces, but none of this was planned or memorized. Instead, through proper training, they have learned to focus on the true goals as they drive, and that was simply the result.
I hope you enjoyed this lesson and if you have any questions, please use the comments section below. Up next, we’ll look take a deeper look at the physics of trail braking. If you are interested in a complete guide to the physics of racing, we also offer The Science of Speed book series, available through our bookstore or at popular retailers such as Amazon.
