Welcome to the fourth part of this racing concepts series. Remember: the most dangerous words in the English language are “I already know that.”
Here we go.
A racing track is typically quite wide, leaving you with many options to place your car in various lanes.
As you’re probably well aware, the fastest way around a race track is not the shortest distance, but the straightest path.
This optimal path around a track is commonly known as The Line.
If you aren’t already doing so, driving The Line produces the most potential for being faster.
In autocross it’s important to understand that the cones are simply boundaries that give you ample opportunity to create The Line.
One of a racer’s main goals is to navigate each corner by finding the path which follows the largest radius.
A larger corner radius will allow a vehicle to remain at a higher speed than a lower radius.
In other words, a more gradual change of direction will allow the driver to be faster (Figure 7).
This is why you see racing drivers dive down to the inside of the corner and then easing out to the opposite side of the track at the exit.
You may also see them crossing to the other side of a straight to set up for the next corner.
When analyzing an entire track this method lets the driver create the largest cornering radius in each corner, and therefore allows for a higher speed throughout the track.
This is why covering a longer distance is actually faster.
Using The Whole Track
Using the entire width of the track is very important when driving The Line. Even a couple feet of unused track can kill your speed in small increments that add up quickly.
For example: If a driver approaches the corner while leaving two feet of space between his tires and the grass he will be forced to enter at a slightly smaller corner radius, which will reduce his speed potential speed.
In racing, the apex (sometimes called the clipping point) is where the car dives down and touches the inside track boundary at the optimal point in the corner.
You can also imagine that if the driver leaves distance between his inside wheels and the apex, it will also decrease his corner radius.
Prioritizing The Track
There are some sections of a race track that are more important than others.
Generally a car will spend more overall time accelerating than braking or cornering, so it’s obvious that straights are very important.
But because the corner before a straight directly relates to how fast you can go on the straight, corner exit speed is the most important factor on the track.
Let’s say that a car is capable of accelerating 30MPH from the corner exit to the braking point at the other end of the straight.
The driver who exits the corner at 38MPH can accelerate to 68MPH. But the driver who exits at 42MPH will reach 72MPH.
Obviously, a higher speed allows an object to cover distance in a shorter amount of time.
If you’re faster at the corner exit going on to the straight, you’ll get to the end of the straight in less time.
Since corner exit speed is directly affected by corner entry speed, corner entry is the next most important area on the track.
Let’s consider the most and least important sections of a racetrack–long straights and short straights.
In Figure 8, the end of a straight turns into a right hand corner, which is followed by a short straight and then a left hand corner.
In this example, the left hand corner opens on to the longest straight on the track.
Immediately you know that the left hand corner is a crucial section to have high exit speed.
And because the straight between the two corners is very short you know that it does not offer much potential for decreasing lap time, so it is relatively unimportant.
In this case it will be beneficial to hit the apex farther past its geometric center than normal and purposefully drive a smaller radius through the first section.
In autocross you’ll frequently hear instructors and “instructors” referring to this as giving it up – giving up entry speed in trade for the exit speed.
I never cared for this term. It’s wishy washy and a little too ambiguous to explain what’s actually happening.
Anyway, this allows you to set up for the left hand corner and drive the largest radius possible to maximize your speed onto the following (and more important) straight.
This is called late apexing. The choice to drive the first corner slightly slower results in faster speeds on the long straight, and faster overall lap times.
Corner Exit Speed
If corner speed is the most important factor on the track, how can you maximize your exit to gain the most speed down the following straight?
There are a couple ways to look at this problem.
Let’s start by looking at Figure 9, which shows the cornering path of a fantastic driver who is driving right at the vehicle’s limit.
If he makes a perfect corner entry at 45MPH and uses 100% of the cars corning traction through the corner, he will exits the corner at 45MPH.
Using the previous example he can now accelerate down the straight with an extra 30MPH for a total of 75MPH at the braking point, which is the best we’ve seen so far.
Before the straight, he achieved an average corner speed of 45MPH.
Now let’s reset the scenario on the same corner and straight for Figure 10. This time, however, the driver enters the corner at 43MPH.
As he concludes his braking before the apex, he begins to accelerate through the corner.
At the apex his speed is 45MPH, and at the corner exits he reaches 47MPH!
This driver has achieved the same average corner speed of 45MPH, so no time is lost due to a slower entry.
But the driver is now able to reach 77MPH at the end of the straight.
Clearly, the second method will be faster.
This is possible because unlike the first scenario, where the driver is using 100% of the cars traction for corning, he is trading forces on the exit.
As he begins to unwind the steering, more traction becomes available for acceleration. We will discuss these ratios later.
Increasing/Decreasing Radius Corners
It would be helpful if race track designers used only rulers and a drawing compass.
That way every straight would be, well, straight and every corner would be a perfect arc.
But apparently shapes and squiggles are much more interesting.
It often happens that the radius of a corner will increase or decrease as the corner progresses, which makes driving the fast line more tricky.
The best way to navigate a changing radius corner is to modify your clipping point.
In figure 11 you can see that while approaching a decreasing radius corner the driver chooses to stay wide for much longer as he enters the turn.
This allows him to carry a higher speed for longer as he leaves the straight.
He then chooses to apex the car rather late, allowing him to create the biggest radius path and to get back on the throttle as soon as possible.
Remember: exit speed, exit speed, exit speed.
If the driver turns around and goes the opposite direction, you can see how he navigates an increasing radius corner. Dealing with an increasing radius corner the driver apexes the turn early and begins a long and gradual exit to create the largest radius for maximum speed at the exit point.
Track analysis gets complicated in a hurry when you add banking, varying levels of surface types throughout the track, weather conditions, elevation changes, traffic, a power decrease from a failing component, and the list goes on.
The preceding post will cover 95% of the conditions you will encounter at most locations. I strongly encourage you learn more about the other 5%, which falls outside the scope of this series.
- Most of the time, The Line will be the fastest way around the track. Watch what others are doing, and if you think you can make improvement based on logical reasoning, give it a try.
- Straights and the corners that lead up to them are linked together. Longer straights have the most important corners before them.
- Don’t be afraid to purposefully drive a little slower through a short section to set up for a long one.
- Improvements to corner exit speed can result in excellent reductions in lap time. Remember: entering slower and accelerating sooner will make you faster.
NEXT WEEK: Tire Management
The next part in this series is only a week away. Go back and read through this again. Make sure you truly understand what you just saw, because the series progressively builds as it continues.