Determining the correct acceleration point is a key part of optimizing a racing line, so in this lesson, we’ll go over a simple way to visualize and understand why the ideal acceleration point is at the apex and why straightaway length doesn’t affect the ideal line through a corner. This doesn't mean that every driver should accelerate at the apex every time however, so make sure to read through to the end of the lesson to find out why. |
This lesson starts a new series covering the core principles of racing line theory, and I wanted to start off with the acceleration point because, not only is it central to line theory, but was also my first “Eureka moment,” in regards to racing.
When I first started racing in the 2000s, as many analytically minded people often do, I read everything I could get my hands on in my pursuit of knowledge and speed. I delved deep into data analysis, vehicle dynamics, and picked up all the driving technique books as well. With my background in physics, my primary aim was to piece together the principles that governed the ideal racing line. As is depicted in this illustration from Going Faster, the Skip Barber book on race driving, one common theme in the driving technique books was that a driver should generally begin accelerating prior to the apex. The apex is the point on the inside of a corner that a car passes closest to. While some of the driving books didn't make a direct recommendation regarding the acceleration point, the ones that did usually showed that it was before the apex, but didn't seem to offer clear advice on where exactly this point should ideally be. |
One problem is that the racing line is often simply drawn as circular in shape or is hand sketched and sometimes includes sudden radius changes that are not even possible if a car is driven at the limit. If however, the racing line is drawn to accurately depict the relationship between line radius and speed, a lot can be revealed. An important vehicle dynamics principle to understand is that when a car is driven at the limit, its speed and line radius are linked. A higher speed requires a larger radius. What this also means is that when a car decelerates into a corner at the limit, the curve of the line it travels on will become tighter and its radius will progressively decrease. Likewise, as the car begins to accelerate, the curve of the line must open up as the car gains speed and therefore its radius will increase. |
This principle makes sense if we understand that, by its very nature, an apex is the point along the inside of the track that is most limiting a vehicle from going faster and must be optimized for. If a driver begins accelerating somewhere other than an apex, they are effectively optimizing the corner around an additional imaginary obstacle. I started calling this a false apex because it would be the same as putting a cone out on the track at the point the driver begins accelerating that they are now also having to clear in addition to the actual apex.
Another common theme I often saw in the driving books was that straightaway length affected the ideal line through the corner. The idea being that since additional speed at corner exit carried all the way down the straightaway, a driver should modify their acceleration point accordingly to take advantage of this. I do want to point out here that once the straightaway between two corners gets short enough, it does have an effect on cornering technique, as they must now be optimized together as a chicane or double apex. We’ll cover these in upcoming lessons, but unless the straight is short enough for this to happen, it’s important to understand that a corner should be optimized the same way regardless of straightaway length.
While it is true that additional corner exit speed will shorten time down the following straight, the problem with trying to accelerate early to take advantage of this and why I wasn’t seeing top drivers like Greger doing it relates again to our previous early acceleration problem. Looking again at our line comparison illustration, it is true that the earlier a car begins accelerating, the faster it can be traveling as it passes a given point at the end of the corner. This is at the cost however, of a progressively tighter and slower line beforehand that will cause it to take longer to reach that point. Now if an early accelerating car could minimize their time lost through the corner enough that their extra corner exit speed could make up the difference down a straight, then there might be something to this.
We made a video several years ago, which I’ve linked below, that includes a section demonstrating this principle by overlaying two different lines from the same car. In the video, you can see how the early acceleration line reaches 67 mph as it crosses a finish line at corner exit, whereas the ideal apex line had only reached 64 mph as it crosses the finish. The key however is that, at the same point in time that the early acceleration car reaches 67 mph, the ideal apex car has also already achieved 67 mph, but is 46 feet past the finish. This actually represents a best-case scenario for the early acceleration car, as it was at least able to get back up to speed from its tighter apex at the same time as the ideal apex car, but since it traveled a longer distance around its false apex, it is 46 feet behind. Since they would both be accelerating from the same speed of 67 mph at that point, the ideal apex car would maintain its 46 foot advantage down the following straightaway, regardless of its length.
As we wrap up this lesson, I want to emphasize that while learning racing line theory is an important first step as it is useful for analysis and understanding the ideal technique, a driver isn’t supposed to simply go out on track and apply these principles directly to immediately produce perfect corners. That usually doesn’t work. Instead, I advocate a progressive approach where a driver learns to gradually internalize these principles so they can actually begin to feel the physics at work out on track. Part of this process is learning the relative time penalties for different types of mistakes. In this case, for instance, it is important to understand that not accelerating until after the apex will generally have a greater time penalty than accelerating before the apex. Sometimes much greater, depending on the car and corner. This fact is surely the reason the classic advice to simply begin accelerating somewhere prior to the apex originated in the first place, as it works pretty well for newcomers. While top drivers like Greger Huttu show us what’s possible, attempting to mimic his technique without having the underlying skills can often result in worse times than starting with a more conservative approach using earlier acceleration. Then as a driver’s skills improve, they can push closer and closer to the ideal.
It’s also important to understand that while we can understand and visualize the perfect corner, we can never truly achieve it. Even the very best drivers will have constant imperfections in their line and every little imperfection will then change the ideal line for the rest of the corner. It is a constantly moving target and even though we can understand why the ideal acceleration point is right at the apex, a driver can’t simply apply throttle as they pass it because their line up to that point is not going to be perfect. Imperfections might cause their current ideal acceleration point to end up being slightly before, slightly past or even slightly outside the apex. While this wouldn’t be ideal if the entry was done perfectly, it was as close to their current ideal as the driver was able to achieve that time. Learning the strategies to constantly push your line as close to the ideal as possible is where true speed comes from.
I hope you enjoyed this first installment in our new line theory lesson series and if you have any questions, please use the comments section below. Up next, we’ll look at the factors that determine the ideal apex and line through a corner. If you are interested in a complete guide to the physics of racing, we offer the Science of Speed book series, starting with The Perfect Corner, available in paperback or ePub. We’ve also just released a new Paradigm Shift Driver Development t-shirt and are making it available at cost, so make sure to take a look at that as well. Adam Brouillard |