Introduction To Data Acquisition
Published: February 25, 2013
This post is aimed at drivers who are starting to use a data acquisition system. I will describe some practical uses of data acquisition that can be employed right away.
Before reading this post you should read the Self-Evaluation page, where I go over the following applications of data acquisition:
- Absolute lap times
- Lap times within a session
- Theoretical best lap time
The first two of these do not require a data acquisition system - if you have a transponder or are otherwise running an event where you are being timed, you can use official times instead of data from your own data acquisition system. Theoretical best lap time requires track segmentation and therefore a data system in your car. However, having a data system gives you access to lap times whether the event is timed or not.
Minimum Skill Level Required
Before we continue with the discussion of data, I want to note that using a data acquisition system both on track and off requires a certain skill level from the driver. If you are looking at your predictive lap time while driving you should do it quickly enough that you do not lose control of your car. It is easy to check lap time while on a straight; doing the same in a corner demands that you do not dedicate 100% of your attention to keeping the car on pavement through said corner.
Evaluating data both on course ond off also requires a reasonable degree of consistency. When you are looking at two different approaches to a corner, the difference between consecutive attempts of each approach should be less than the difference resulting from varying the lines, or all you are measuring is jitter.
Now, to the exciting part.
Using Yourself As Benchmark
If you do not have any other drivers to use as a benchmark, you can always use younself. If your car managed to take a certain corner at a certain speed once in the session, there is generally no reason why you could not take that corner at that speed every lap in your session. Data acquisition allows you to see what your car can do, which corresponds to your best lap time or segment time or minimum corner speed, etc. You can then try to achieve that time or speed consistently; as you are working on it, you will not only improve your skills, but likely exceed your benchmark at one of the laps which immediately gives you a new goal to work on.
Compromise And Combination Corners
Suppose there is a fairly long straight followed by a sharp left followed by a sharp right, not unlike turns 4-5-6 at Summit Point Main. The S turn line dictates essentially late apexing the first turn to set up for the second turn. However, this means the first turn is taken very slowly, and especially that braking is performed on the straight leading up to it which means the speed that was carried on that straight is thrown away. What if instead the first turn was thrown away, braking as late as possible into and through the actual turn, to preserve the high speed on the preceding straight for as long as possible? Would this be better than the "standard" line? Would a compromise between these two ideas be the best?
Such questions are impossible to answer by the seat of the pants. This is where data acquisition comes in. The most important tool available to the driver in the car is predictive lap time. What this does is it shows you, in close to real time, whether you are doing better or worse on the current lap than you were on your best lap so far. Therefore, if you start with a traditional line to establish a baseline and then try the throwaway line, you will see right away if this saves you time in the first turn (it does), and if you come out ahead as you get onto the next straight (you may or may not).
Are you using all of the car's potential under braking? Forward G graph will quickly reveal the answer.
A noticeable difference between a beginner and an advanced driver is in how much of the friction circle they use. A beginer driver would apply maximum braking, then get off the brakes completely at which point the car has no forward and no lateral acceleration applied to it, then turn into a corner. Trailbraking done by novices is usually unintentional and eliminated by instructors via a phrase similar to "brake in a straight line, then turn". This is because novice drivers usually would not be able to correct oversteer resulting from excessive trailbraking.
Looking at a G-ball, or a combined plot of lateral and forward Gs, would reveal a dip around turn in point. In contrast, advanced drivers transition from full braking to partial braking and partial turning to full turning. On a G-ball the ball travels along an arc from full up to full sideways. On a combination plot the minimum G stays close to maximum G.
It is very hard to detect how far you are dropping combined Gs by the seat of your pants. The same information is trivially obtainable from a data acquisition system.
Corner Exit Speed
This is something that many HPDE programs mention as a benchmark, except they want you to look at the RPMs or speedometer as you are exiting a corner. As the difference between a good exit and a great exit is often less than 5 mph, you need to sample whatever instrument you choose to reference at precisely the same point every lap for the sampling to be meaningful. Most of the time it is not.
In contrast, with a data acquisition system you can simply overlay speed vs track position over multiple laps and compare speeds at exactly the same point. This is obviously done after the session, which means you need to have some way of identifying what you did on each of the laps in question.
Overslowing The Car
You can lose a lot of time, say 0.75 seconds in a single turn, by braking too much. You can look at the minimum speed in a corner over multiple laps to determine if you are overslowing the car. There obviously is an absolute maximum speed at which the car is able to take that corner. There is also the highest speed at which you succeeded going through the corner. The goal is for the minimum speeds on other laps to be close to the highest minimum speed you attained. Once you know your highest minimum speed and jitter that you accept (say, 80 mph and 2 mph), if you have a digital speed readout you can (carefully) look at it at the apex to see how well you are taking the turn. Staying close to the highest minimum speed and keeping the car on pavement is a very good indicator that you are close to using all of the available grip.