Telemetry: trail-braking

I’m relatively new to telemetry analysis, but I thought I’d share some of my experiences. The product I use is an Aim SoloDL. The companion software is called Race Studio Analysis. I don’t really like the software, but it’s better than several competing products. Rather than show you traces from my real racecar, I thought it might be more useful to use a simulator. That way you can call me names after you beat my lap times.

The simulator we’ll use for this is Assetto Corsa. Earlier this year, I posted on the state of the art in racing sims, and if you want to see a comparison of what’s out there, check that out. AC is one of the better sims, and possibly the best place to start. I’m using the Brands Hatch Indy track and the NA Miata. Just to get lap times out of the way, I usually lap in the 1:03-1:04 range. I’m sure someone who is more familiar with AC and Brands can take a couple seconds off that.

The point of this post today is to look at what trail-braking looks like from a squiggly line perspective. Trail-braking is a term that gets thrown around as an advanced cornering technique. It’s actually pretty simple: gradually release the brakes as you turn into a corner. This is in contrast to the more basic technique of separating pedal input from steering input. The reason it’s an advanced technique is that the rear of the car gets light under braking. So if you turn with the brakes on, the rear can rotate around and cause a spin. So why do it? I think most people will tell you that it’s because it saves a few tenths here and there. But the reason I do it is because I like getting tactile feedback from the steering wheel under braking. It helps me judge my corner entry speed.

So let’s say you just ran a few laps in Assetto Corsa. How do you get this into Race Studio Analysis? It turns out to be super simple. You’ll find the telemetry file in your Documents folder (open the Assetto Corsa folder there and then the aim folder inside that – there’s only one file ever in there). Race Studio Analysis can import this file. I don’t have enough time in this blog post to show you how to configure RSA, so let’s skip to the view of squiggly lines. I want to draw your attention to the parts marked A, B, and C.

The point marked A is Turn 1, which is a tricky downhill right-hander. The top row is speed, and you can see that the blue line has much more speed through corner, but the black line later catches up. That difference turned out to be 0.5 sec (bottom row). Look at the 3rd row (brake pressure). Do you see how the black line is on then off whereas the blue line tapers off? That little bit of braking while turning (4th row) is the sign of trail-braking. The 0.5 sec difference is more than usual, and had I carried more speed on the black line, the difference would have been half that.

Point B is more interesting, and you should look for it in the video below at about 1:53. The car is mostly straight as it goes through the apex. Do you see the dip in the steering angle of the blue line? With more weight on the front tires, you can turn more. What’s really important is the recovery after that. The car is steered in more aggressively while braking, and then counter-steered as the throttle is applied. The car on the black line can’t rotate as fast and can’t get to throttle as quickly. The result is about 0.4 sec. Point C is similar to B in that the car is at full throttle sooner because the car gets rotated earlier.

The cumulative effect of trail-braking a few corners turned out to be about 1.4 seconds. That’s probably a little bit of an exaggeration because I don’t normally separate my inputs, so it felt a little odd to me. But certainly there’s 0.5 seconds in the technique even on a very short track. More importantly, I think trail-braking makes you feel more connected to the car, and for me, that’s where the enjoyment is.

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