Backing up the corner

When you first start driving on track, the most common phrase you hear is in slow out fast. That’s generally a good idea for safety and lap times. Some drivers think they can go faster by holding more speed, but if they have to lift at the exit, it’s an overall loss. Another misconception is that one can reduce lap times by braking harder and later. This is only true for the novice who has no confidence in braking.

When people talk about advanced driving techniques, the most common topics are heel-toe shifting, trail-braking, and left-foot braking. All of these are physical things one does. All can improve lap times. They are considered advanced because they take some physical coordination and practice to apply. Doing them badly can get you into trouble. But the upside is lower lap times and a greater feel for the car. Myself, I trail-brake almost every corner and heel-toe shift every time. I don’t left-foot brake because I haven’t practiced it enough.

What about advanced techniques on the mental side? That’s the topic today. I want to talk about backing up the corner. You may have heard that phrase before and wondered what that was about. It means getting the braking, turning, shifting, and throttling done earlier in the corner. This technique is especially important for low powered FWD cars like mine.

There are two things to consider when backing up the corner, the mental discipline to do it, and the physical ability to execute it. Let’s talk about the mental side first. You must first recognize the nadir of the corner. As far as I know, that’s a term I made up. If every corner has an apex (top) it should also have a nadir (bottom).

The nadir of a corner is the point of lowest speed.

Where exactly is the lowest speed in the corner? Usually at the place where your cornering G-forces are highest. If you think back to your traction circle, the traction of your tires can be used for braking, cornering, accelerating, or some mixture. So max cornering is not under braking or accelerating, but strict cornering. If you’re trail-braking into a corner, which you should be doing most of the time, the maximum cornering should be at the time you’re taking your foot off the brake and moving it to the throttle (assuming you right-foot brake). If you want to back up the corner, you need to move the nadir earlier on the racing line.

That seems simple enough, right? Just do everything a little earlier. Well, it’s not that easy. If you want to be on the typical racing line, you’ll need to get the car pointed straight earlier. Simply braking and turning earlier will see you hitting an early apex and running out of track at the exit. You have to rotate the car early in the corner without losing speed. That means you have to slide the rear of the car out, countersteer to keep it on line, and add throttle before you’re fully straight.

Let’s take a look at what that looks like in telemetry. You’ll probably want to click on this image to see it full size as it’s pretty large. The track is Laguna Seca. The panels are speed, RPM, throttle, and time going top to bottom.

Point 1 is turn 1. The blue driver has shifted to 4th gear here. That’s why there is a 4 in the RPM panel. The time panel (bottom) shows there isn’t much difference switching to 4th briefly vs. banging off the rev limiter. When I saw this, I drove in 4th for my second stint as it’s nicer to the engine.

Point 2 is turn 2. The two drivers have very different approaches to this. The red driver does a double apex while the blue does a single. As you can see from the time graph, the double apex loses a bit of time and then makes up for it. Double vs single apex isn’t really the conversation today. Instead, I want to focus on the three 90° corners that follow. As you can see from the time panel, the red car gains a lot of time here.

Looking at the speed graph (top panel) it looks like the red line is shifted left compared to the blue line. This is especially apparent at points A-D. This isn’t a GPS alignment issue. It’s the red driver backing up the corners. Unfortunately, I don’t have a brake sensor on the CAN bus, but one can infer that the red driver must be off the brakes much sooner than the blue. He doesn’t necessarily get to full throttle sooner than the blue driver, and in some cases later, but he’s applying the throttle sooner. The points marked W indicate wheel spin in the RPM graph. The red driver is clearly trying to maximize throttle and steering because he’s at the limit of both (sadly, the car has an open differential).

How important is backing up the corner? Like other advanced techniques, it’s something that can drop lap times when done properly and a bit hazardous when not. It’s fun to work on. Like other advanced techniques, I suggest working it out on a simulator rather than a track session, and never on the street.

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