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The belligerent old codgers guide to data logging.

It doesn’t make your engine more powerful, or give the brakes more bite and it certainly doesn’t give your tyres more grip.
It just sits there, looking at you, silently taking notes like a robot driving test examiner.
So why does every top level car have one, what’s the big fuss about?

A data logger records info from the sensors you plug it into, and there is a huge range of possibilities here, but typically it will record road speed, engine speed and accelerator pedal position as a basic set. From this you can see if you change gear at the right speed and how well you use the engine and gears. Many now record acceleration (including cornering force) and your position on track from GPS data, thus giving you a plot of how fast you were as you go through each corner. This type has become significantly more affordable and there are many units available for under £500, it’s this sort I will concentrate on here.

This data gives you two benefits:
1.It tells you accurately how well the car goes.
2.It tells you objectively how well you are using the cars abilities.
It is this second point that is often the most valuable.

First let’s look at some data so that you know what I am on about. You can see from the screen shots how the logger traces out your position round the track, you can then put way points in, on the laptop, to mark out bits of the track that you are interested in, such as entry and exit speeds for each corner.
Once you have put these points in then you can call up the data as a table or as a graph, depending on which is easier to read.

But why bother with all this gubbins? As an example consider a test day for a circuit racer, you do ten laps at full tilt. As you settle in to a pace your lap times fall and become more consistent. So far so good. Normally you would check the tyres and if everything seemed optimised you finish the session satisfied.

In reality you probably took each corner very slightly differently each lap, how you go into one bend effecting the next. If you look at the data loggers print out you can see the differences lap to lap, one corner may stand out as having a high variation in speed (that will be the one that never really felt quite right). Now if you look at the data you can see what gave you the best results, what speed you went in at, where did you start accelerating, where did you turn in etc. With this knowledge you can now go back and try to get that corner just right, something that’s very difficult to do with only lap times.
You can also construct a ‘dream’ lap. Take the best times for each corner and add them up. This gives you a lap time that you could do if you got every corner done to the best of your current ability.

Well that’s not entirely true, some times you have to trade speed at one corner to get the best out of the next, but you get the general idea. Its about showing you accurately where you can improve.
Common faults for those of us new to racing are hesitation moving from accelerator to brake at the end of a long straight, hitting the rev limiter when changing up and coming back on the power too early or late. All of these can be seen clearly in the data traces. <example traces>

Getting real accurate data is very valuable when you are making modifications to the car set up or tune. Often a car can feel quicker just because it requires more concentration, but this could be simply because the power delivery is harsher or the steering is more twitchy, or even because you forgot your ear plugs. As an example, if you are trying different damper settings you can see exactly how this changed the entry and exit speeds of a corner.

Recording suspension movement is very useful on off road racing, seeing how often you hit the bump stops and when the wheel is at full droop (off the ground) can help you get the most out of the suspension and thus the available traction.

Interpreting the traces is something of a skill, and if you have never done anything like this before then its worth spending some time with someone who has used one before to learn the ropes. If you look at the traces of the hair pin at Mallory you can see the different lines taken on each lap, you can then call up the data showing which line was fastest. With a bit of practice you can also see which is the best line when overtaking too.

Fitting one is relatively straight forward, depending on how many extra sensors you want wired in.
At a basic level you can fit the unit near the middle of the car, feed it 12 volts and tape the GPS aerial to the roof. This will give you accelerations and your position on the track. Not a bad start.
More use can be had by feeding in accelerator position and brake pedal position. If these two don’t already have sensors on (for engine management etc) then you will have to fit one. This can be home made from a potentiometer and a couple of bent bits of ally, the same arrangement can also be used for suspension movement sensing so that you can record roll, dive and squat.

Connecting up road speed and engine speed, from the ignition LT side or crank sensor, will help you hone your gear shifts and if you compare your road speed sensor with the GPS speed you can see where you get too much wheel spin on the start line.
That lot is fine for most club level racers and will give you many happy hours of honing.

Going a step further you can record each individual wheel speed and steering angle in order to start analysing yaw angle, slip rates, under/over steer and steering effort. This can be used to hone the driver and the car set-up too.
Further still, you can record all sorts of temperatures, pressures and suspension movement, but you need to know what to do with the data to get any benefit from this. If you are in that game then you probably already know about data loggers.

There is a huge range of units available, the simplest is a rev counter with a memory and a playback function. This is excellent for drag racing where gear shifts are critical. Then there are digital dash boards which record and display sensor data, typically engine and road speed, engine temperature, boost pressure and other things you would expect to see on a dash.
Then there are the stand alone ‘black box’ units with a number of speed and voltage inputs plus an in-built set of acceleration sensors to tell you braking, acceleration and cornering forces.
The ones that combine this with GPS data can give you a nice picture of the race track and overlay how well you were doing on top of it. I like pictures, pictures are good.

This Racelogic unit can accept sensor inputs or work as a stand alone unit with G sensors and GPS tracking.
I used on in Runningblade, the world land speed lawnmower!
Mallory park with traces for each lap, the green dots show where virtual timing gates are set up to measure sector speeds.
The hairpin at Mallory showing all the different lines taken during practice.
Getting into the detailed data.
Graphs are usually easier to understand than numbers.
All you need is a cheap laptop to look at the data at the race track.

©Ralph Hosier