Chalk Talk: the nadir

When coaches talk about driving techniques in the classroom, the conversation generally begins with the racing line. This is broken down into 3 component parts: turn in, apex, and track out. I find that students really latch onto the apex as the most important part of the corner. It might be the most obvious part of a corner, especially when coaches stick an orange cone on the track, but the apex is not the most important point. The apex impression apparently stays with them a long time, because even advanced drivers have a tendency to focus on the first part of a corner and have no idea what the second half of a corner is supposed to feel like. That’s the subject of this Chalk Talk.

A constant radius corner is not driven with a constant radius!

One way to think about a simple 90° corner is that it has 2 parts: a small radius in the beginning and a large radius at the end. The only way to get from a small radius to a large radius is to UNWIND THE WHEEL. That is, if you’re in a right turn, you have to steer back to the left when you want to increase your speed. When should this happen? No, it’s not the apex.

In the diagram below, the green arrows labeled “1” and “2” have different radii. Curve 2 has a radius about twice as large. The break between the arrows is called the nadir of the corner. It is the point of lowest speed on the racing line. It’s the point where you transfer from brake to throttle and the point at which you start unwinding the wheel. It is the most important part of the corner. Unfortunately, it’s not so easily labeled because you can’t stick a cone on it. Yeah, racing is hard.

unwinding

The red line traces a constant radius. Lots of advanced drivers are actually on this line even if they disguise it. They corner at constant speed and then add throttle after the apex. They may even obediently steer out to the edge of the track in the belief that they are on the racing line… they are not. The racing line isn’t just where the car goes, but also how the car goes.

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