For more information on how I’m collecting this data, take a look here.
First off, how does my data compare to the official data? Bayford Meadows use alphatiming as their timing system and it’s those number that really matter. One of the limitations of my app is that it only has an accuracy down to 0.1 seconds where as alphatiming goes down to 0.001. Still, my lap times are pretty similar – they’ll never be exactly the same as I’m not measuring from exactly the same point.
- Officially, lap 1 was 1:00.918 but I recorded it as 1:00.940
- Officially, lap 1 was 59.768 but I recorded it as 00:59.780
- Officially, lap 1 was 59.900 but I recorded it as 00:59.910
LapTimer is clever enough to group laps into sessions depending on how many breaks there are between laps. For the purposes of this post, let’s take a look at qualifying for Heat 4. Why that session? Easy, it’s the only one that the accelerometer in my iPhone worked on. I’ve still got a couple of kinks to work out!
As you can see, there’s a bunch of filters and tags available so once you have several sessions recorded it’s easy to find the ones you want.
The first thing that LapTimer gives you is a map of the lap with various options:
- Lateral acceleration that I can use to see how hard I’m steering and which way the Kart is being pulled
- Linear acceleration shows whether the Kart is accelerating or braking. I think this is how it works anyway – I’m not quite sure on this one. If you do know, let me know please!
- Accuracy shows the GPS plots with the size of the ‘splodge’ indicating how confident LapTimer is that it has me in the right place.
- Reference puts the line that I followed in the chosen lap on top of the reference lap. Usually I’d have my fastest lap as the reference but in this case I’ve set it to be the first lap of the session. The reference lap is in red, the selected lap in grey.
The lateral acceleration chart is showing us the g-force the Kart is sustains throughout the lap. The size of the block indicates how severe the g-forces are while the direction is shown by the side of the block relative to the direction of the Kart (from the Start/Finish the Kart is travelling clockwise).
It’s configurable so different colours are shown depending on the force at the time.
Looking at the chart, it’s clear that the biggest forces are experienced in Turns 2 and 9 when the force is pulling me out of the corner – these are also two of the fastest points on the circuit. The Kart is also under high force in Turns 3, 6 and 7 but in these cases the force is pulling me in to the corner.
I freely admit that I’m struggling to understand what this chart is showing. Again – if you can help me read it please let me know either here or through one of my social channels.
I’d expected the chart to show where I’m slowing/accelerating but that’s not the case since the heaviest braking zones, before Turns 2 and 10 are all green while the exit of Turn 2 is red and I’m definitely accelerating here.
This is the chart which is the least useful to me at the moment. Before I bought the Dual device the accuracy provided by the iPhone was pretty poor but this is much better. When the route is overlaid on Google maps there are still a few inaccuracies but it’s good enough for now. If I get a lot of use out of the telemetry I might look at getting a more precise device.
There’s an interesting discussion about accuracy and precision in GPS devices which it’s worth mentioning here. In a nutshell, an accurate device will report the same position when visited multiple times. For example, If I’m on the inside at Turn 2 I’m always recorded at the same point on the track. A precise device will record me at exactly the part of the track that I’m on. In an ideal world I need to have a device that is both accurate and precise but for now I’ll settle just for an accurate one.
This is where things get interesting. As I said earlier, the red line is the reference lap – lap 1 in this case – and the grey line is the 2nd lap. I know that while the GPS might not be precise, it is accurate so I can ignore the lack of a map and just look at the lines.
Starting off right at the beginning I can see that I’m already in the middle of the track when I cross the Start/Finish and move over to the left hand side of the track before turning in. I’m further over on the track which gives me a shallower curve to follow through Turn 1. It looks like I was smoother on the steering input too. In Turn 2 I went wider and then turned in more sharply which is the faster line through here when you’re not racing.
Turn 3 is very similar on both laps but Turn 4 is interesting. Zooming in, I can see that although I went deeper into the corner on this lap I was able to take a tighter exit on lap 2 which set me up for a slightly better entrance for Turn 5. The GPS is a bit “square” here so I assume that it lost some of it’s accuracy and I can’t see the exact line I used. In any case, I was up on the kerb out of Turn 5 using the extra bit of track to get a good top speed down the straight and into Turn 6. I can see from the earlier chart that I was doing 40mph before I braked. The line through Turn 6 is very different – by braking deeper I was able to turn the Kart more sharply, still hitting the correct, late apex and setting myself up to run flat out through Turns 7, 8 and 9 where the lines are very similar other than staying tighter through Turn 7 on the second lap which allowed me to carry more speed through 8 and on to the straight. I was closer to the kerb through Turn 9 on lap 2 and had a much better line through my favourite corner, Turn 9. I stayed on the right hand side of the track and started to move over just after the Start/Finish straight.
There are 2 variants of this graph – one with the time difference between the laps showing and one without it.
Both are showing the speed at the different points of the track for both laps. This allows me to see where I’m faster on one lap and where I’m slower. For example, I can see that I had a higher speed through turn 1 on lap 1 than I did on lap 2 although I was smoother on the 2nd lap. The time difference shown in the 2nd chart indicates that although I entered the corner slightly up on lap 1 by the time I exited the corner I was down on time. I recovered that on the straight from a better exit and was back in front before arriving at Turn 2. This proves out the old racing maxim of ‘slow in, fast out’.
The time difference chart shows that there are clearly points on the 2nd lap where I’m losing time compared to the first. Even though the speeds through Turn 4 look similar I lost a lot of time here but quickly recovered it. I know from the reference lap chart that the lines here were different – with a much smoother exit. The data would suggest that taking the corner slower, allowing me to use the entrance and apex from lap 1 and the exit from from lap 2 would be the best way to take the corner. It’s a similar story through Turn 6 and 7. A better line and Kart control leads to an initial drop in time which is quickly recovered and improved upon. The remainder of the lap is clearly much better than the first!
There’s a lot going on in this useful graph. Although I struggle to understand the lineal acceleration chart, the graph is clear to me. There are 4 data sets:
- The red line is the lineal acceleration of the reference (1st) lap
- The grey line shows the lineal acceleration of the 2nd lap
- The grey area shows the time difference between the 2 laps
- The dotted line shows the lateral acceleration on the 2nd lap at the same point on the track.
So what’s this telling me? I can see in the 2nd set of peaks that I had a higher top speed here, correlating to just before braking at Turn 2 (each trough is a corner). This small gap led to a much higher top speed, maintained for longer down the straight into Turn 3 which was roughly 0.3 seconds. There’s plenty more going on here and I’m on starting to understand this even as a I write!
Lateral Acceleration/Speed & Overall Acceleration
These last 2 graphs are less interesting to me at the moment. The 1st is identical to the linear acceleration graph but showing lateral (left and right) forces along with the time differential. The last shows the overall acceleration. I’m a long way from being able to get anything useful from this at the moment
I’m sure that when I combine the data with the footage from my GoPro I’ll be able to extract plenty of useful data that will help me to improve my times. Over the next week or so I’ll take a look at my best lap of the night and compare it with some of the others and see if I can identify some areas from improvement or frequent errors.