GHIT extra: racing lines

I was recently interviewed on the Garage Heroes in Training podcast and they asked me a lot of really interesting questions. I want to follow that up in a series of posts on YSAR where I get into a little more depth on a few topics.

The Racing Line vs. the line you drive while racing

Several of the questions were either directly or indirectly related to the racing line. When most of us think of the line we imagine the path we take through a corner that optimizes our lap time, and in the typical 90° corner this would be the standard outside-inside-outside late apex line that we all know and love. However, in an amateur endurance race, this is almost never the line you want to take. When there are 100 cars on track, there are much more important things to think about than optimizing your lap time.

Grip, line, awareness: pick two

When I’m racing, awareness is always at the top of the list. The only time I’ll let that go is if I look behind me and I can’t see any cars at all. But as soon as I’m in any kind of traffic, my mind set is “how do I position myself in case the drivers around me do something unexpected?” If I’m optimizing awareness, it means I generally can’t drive the typical racing line as I’m positioning the car to avoid potential disaster. But wherever that line happens to be, I’m driving near the limit of grip. Ultimately, when racing, I almost always throw away the line and optimize the other two.

Does the angle at the apex matter?

Another question I was asked was if I thought the angle at the apex was important or was it just good enough to be at the apex. The angle is critical. In the picture below, both cars have reached the apex. Car #1 is going to have to do a lot of steering in order to finish the corner. Car #2 may have to make some steering corrections to prevent itself from spinning. In other words, Car #1 is understeering and Car #2 is oversteering. The angle you arrive at the apex determines how much throttle and steering you can use in the 2nd half of the corner.

If Car #2 doesn’t spin, it will win the race down the following straight. Car #2 is ready to go to full throttle very soon. Car #1 will have to wait a bit. If Car #1 gets impatient and adds throttle too soon, it runs the risk of understeering off the exit.

Most novice and intermediate drivers position themselves like Car #1. Why? Because in order to position yourself like Car #2, you must have oversteer in the first half of the corner. Not throttle-on oversteer, but throttle-off oversteer. Most novice and intermediate drivers spin under such conditions. Because spinning will earn you a black flag and the humiliation/penalties that go along with it, intermediate drivers may find themselves perfecting a driving style that prevents the rear from stepping out. You can be a pretty fast and safe intermediate driver but unless you learn to drive with oversteer, you won’t be as fast or safe as the advanced drivers.

It’s easy to see why driving with oversteer can make you faster, but why safer? Because shit happens on a race track. Shit you can’t foresee, like being forced off track, having a tire blow out, getting hit, or driving through oil. When shit happens, your car control skills save you, not your work-arounds. If you’ve learned how to drive a sliding car, your muscle memory and experience will help you navigate a perilous situation. However, if you’ve learned how to avoid sliding at all costs…

GHIT extra: decreasing vs. increasing radius

I was recently interviewed on the Garage Heroes in Training podcast and they asked me a lot of really interesting questions. I want to follow that up in a series of posts on YSAR where I get into a little more depth on a few topics.

“Increasing or decreasing radius?”

That was the question. Which do I prefer? Decreasing. And off camber if possible. Why? Because I like the challenge of balancing traction, and there’s more challenge to do that with brakes (decreasing radius) than throttle (increasing radius). Later, as I was thinking about this again, I came to an important realization: all corners are decreasing radius. Also, all corners are increasing radius.

Geometric line is a fantasy

The geometric line described in nearly every racing book is (a) not possible (b) not optimal.

There is no way to instantaneously go from driving in a straight line to a curve with constant radius. If you turn your steering wheel super fast, as would be required, the car doesn’t respond at the same speed. If you took a snapshot in the middle of a corner, you would see the rubber in the contact patch twisted to some degree and the suspension have a certain compression. But they had to get there somehow. It takes some time for the vehicle to take a set. During that time, the radius is probably not constant, but tightening whether you want to or not.

Not only does every racing book describe the geometric line, they also show the late apex line. The reason why the racing line is faster than the geometric line is because cars have engines. If they didn’t, the racing line would look very different. In fact, it would be decreasing radius. But since cars do have engines, and sometimes very powerful ones, the more time you can spend using that engine, the better. The late apex line trades corner speed at the beginning for corner speed late. In other words, the radius at the start is tighter than the radius at the end.

Every corner is decreasing radius (and increasing)

Let’s break up the corner into 2 parts.

  1. The first half of the corner. This is defined as the moment you turn the steering wheel until the moment you release the brake.
  2. The second half of the corner. This is defined as the moment you step on the accelerator until the moment you are no longer actively steering.

The point between the two halves of a corner is sometimes called the EoB or “End of Braking” but I call it the “nadir” because if every corner has an apex (top), it should also have a nadir (bottom). In some corners, the apex and nadir are really close to each other. That’s because the apex is the point at which the car is closest to the inside of the track and the nadir is the point of lowest speed. Usually, the nadir is a little before the apex. In really long corners, or two corners connected by an inconvenient distance, the nadir may be a stretch of track rather than a single point.

If you’re taking the usual racing line, the first half of most corners has a decreasing radius. You start out with the steering wheel straight. As the car trail-brakes to the nadir, the corner gets tighter. As grip transitions from braking to steering, more steering gets done. Also, speed is decreasing, so it’s possible to drive a smaller radius with the same grip. At the nadir, all grip is use for cornering at the slowest speed. Therefore, the radius is tightest. Even if you weren’t aware of it, the first half of the corner is supposed to be decreasing radius.

In the second half of the corner you’re mixing steering and throttle. As the steering is unwound, more throttle can be applied. The radius increases both because there is less steering and because there is more speed. From nadir to exit, the corner is increasing in radius.

Here’s an illustration to help you picture what I’m talking about. Whether you’re taking the single late apex or the double apex, there is decreasing and increasing parts, even in a carousel. The circles represent the halfway point of the corner as described above. The A’s represent the apexes on the single apex (blue) and double (red) apex lines.