Carrying Speed: Reading Data – What Are All The Peaks And Valleys?

We often hear of racing drivers and crew chiefs refer to collecting and reading data from on-track sessions. Professional motorsport teams have impressive software and telemetry sensors that can measure and record information from systems all over the car and the driver. Most of us club racers and track day enthusiasts don’t have the kind of money required to arm our cars and our bodies with these systems. And if we did, could we even understand what that data tells us? Data acquisition and interpretation is an important tool in fine-tuning driving habits.

As it turns out, one of the most affordable and common lap timers around, the AiM Solo, has a pretty robust data recording and analysis system, and it can tell you what you are doing on-track, even if you don’t know it. You’d be surprised that many owners of the lap timer don’t really know how to interpret or use that data to their advantage. And, even if you don’t have an AiM, most data loggers and/or lap timers can give you the same basic type of information.

So here I am, to give you a fairly basic tutorial on reading and using data to improve your performance. As far as the function of the program itself, you can call AiM or look up one of the many helpful Youtube tutorials to help you. It’s really quite easy to use.

General Overview

First, let’s do a quick overview of what’s on the page.

While the system can monitor numerous items, for us, the two important pieces to study will be Longitudinal Acceleration (top line) and Speed (bottom line).

Above is the general graph and how it looks to you when loaded on the analysis screen. For this example, we have selected one driver (whose name I’ve covered for anonymity), and one lap. You can select numerous laps to study by clicking the boxes at the very bottom of the page, but I’ve just selected lap 3 for simplicity.

The lap starts at the middle of a straight (Start/Finish line) and then the first dip is braking for Turn 1. Then accelerating up to the brake zone for Turn 2 . . . so on, and so forth. Familiarity with the track (or using one of the many embedded track maps available through the program) you can see your speed in various parts of the track.

Speed Over Time

I’ll actually start with the bottom line on the graph, which is our Speed Over Time. Upward sloping lines show us that we are gaining speed. Downward sloping lines show deceleration. Generally, you can expect that if the line is headed upward and then abruptly goes downward, it’s the end of a period of acceleration and the start of a braking zone, likely going into a turn.

This is the graph of Speed Over Time (bottom line). Upward sloping lines represent gaining speed, while downward lines show slowing (but not necessarily the application of brakes).

Longitudinal Acceleration

The next line we are interested in — and to me, one of the most important indicators of a driver’s behavior in the car — is the Longitudinal Acceleration line (upper line on the graph). Basically, this is a line over time that shows positive and negative forward acceleration. When the graph is sloping upwards, the sensors in the data recorder feel acceleration. When braking is applied, the slope goes downwards as the sensor picks up the braking force. Note in the figure below, the braking in Longitudinal Acceleration corresponds directly with the decrease in Speed. We are going to come back to this later in the article.

Longitudinal Acceleration over Time: Downward slope indicates deceleration, upwards indicates acceleration.


You can also get an idea of your maximums and minimums. The red circle on the top left of the figure below tells you the numbers for your lowest and highest Speed, as well as your highest positive and negative Longitudinal Acceleration. The red circle on the bottom right shows the points corresponding to two of those values: maximum negative longitudinal acceleration (hardest braking) and maximum speed.

Maximums, Minimums, and their corresponding position on the track. Here, the max speed is followed by max deceleration, in other words, hard braking at the end of a long straight.

Analysis of Performance

Ok, let’s get back to talking about the Longitudinal Acceleration line.  I’m going to post this graph here so you can refer to it continually during interpretation/analysis.

Refer to this graph as we interpret the information below.

In the very first valley — Turn 1 — we see a steep downward line to mark hard deceleration. That is followed by a small upward rise, then a small (almost) flat line before continuing its upward climb. Consider that we are coming from high-speed at the end of a straight. The first input is hard threshold braking. The more sharply sloped it is, the harder the braking. The short uphill followed by the plateau and the continuance of the upward line is the application of throttle after braking has ended.

Importantly, what the plateau tells us is there was a brief pause in acceleration before the throttle was reapplied. The driver adjusted mid-corner. This could have been to prevent understeer, oversteer, or to redirect the nose of the car due to a poorly judged turn-in. Either way, they missed out on the best possible shot at accelerating out of the corner by having to take their foot off the throttle momentarily. This may not seem like much, but a tenth of a second in each corner over the course of 20 turns adds up to a decent amount of time to either gain or lose.

The second valley has a little “hump” in the middle. The hump simply corresponds to a messy downshift where brake force was released in order to blip the throttle. Notice the slope of the line is less severe than the preceding turn. If you compare it to the speed graph, you will notice the driver didn’t have as high of a speed to brake from in order to make this turn. The acceleration zone between Turns 1 and 2 is shorter than the acceleration zone before Turn 1 of the track.

As you can see, this type of data shows you what your feet are doing. The downward slope of your line shows you how hard you are decelerating and for how long. A thin, deeply slicing V represents one strong, consistent brake application versus a more shallow V which shows less brake force carried for a longer duration. Steady upwards sloping lines show consistent and smooth throttle application, while choppy ones show the driver is needing to adjust their line, or the throttle input amount during acceleration.

It’s very helpful to know how this data is interpreted and matches driver behavior.

Comparing Laps

Now, what can we find out when we overlay another driver’s lap over our own? This is where the program becomes very powerful.

In the above graph, we have Blue driver and Red driver. The first thing that is very clear is the Red driver brakes later, harder, and more deliberately comes off the brakes more often than Blue over almost the entire lap. Notice the braking behavior in Red’s Longitudinal Acceleration is marked by deep, thinner Vs in comparison to Blue’s.

The second thing that stands out is when looking at the Speed graph, notice in Turn 1 and 5 that the blue line is lower than the red line. This means that through these turns, Red carries significantly more speed.

In Turn 5, Red brakes harder, but for a shorter period of time, and keeps higher corner speed through the apex. Then, on the following straight, Red accelerates for a longer period of time prior to braking than Blue. At Turn 6, Red again brakes later and harder, carrying more speed into the turn than Blue, who applied brakes sooner and for a longer period of time.

You can see the time difference at the very bottom of the graph. With Red’s faster lap as the baseline, the rising blue line tells you all you need to know. Sionara Blue, Red is outta here!

Take some time and really look through these graphs and see if you can figure out what is happening behavior-wise. Next time you go out with your AIM Solo, know that it does much more than predict and record lap times. Using its many functions can make you a better driver!

Also, since some will ask, the reason Red’s acceleration out of Turn 1 is less smooth than Blue is because he pretty much slid the car through Turn 1. I was there, he was hauling ass! Smooth is usually faster, but sometimes you gotta just send it . . .

About the author

Kasra Ajir

Having competed, raced, or trained with SCORE, SCCA, NASA, BMW CCA, and more, Ajir is well seasoned in the various series that pollinate the grassroots and professional auto racing world.
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