Track day timing set-up

After completing my first car track day at Knockhill in June, I realised this was something I want to do again. I want to grow my skills, and have some data on how I am improving. I want to analyse my times and approach to the corners Knockhill, and eventually of any circuit I choose to drive on. I know timing on track days is not allowed, to disbar teams from using them as cheap test days, and to try and prevent people from chasing times and driving dangerously. However, it also seems to be very common among the track day crowd, and provided I’m using my kit sensibly and safely, and driving in consideration of the other drivers, it’s safe. Plus the later analysis of the laps really helps me improve as a track driver.

Image of VBox Laptimer display

VBox Laptimer

I researched out-of the box solutions, and principle among these are the various flavours of VBOX kit, notable as it is optional in the  specification and sponsorship of the Caterham Academy cars. The cheapest option here is the VBOX Laptimer at £720, right up to the VBOX HD2 at a shade under £2,500. The Laptimer would give me comparative lap times on a dash-mounted screen, and the ability to download logged data into a proprietary app for detailed analysis later, but it is a long way outside of my price range, and only a partial solution. To get everything I wanted, including synchronised video I would need a VBox Lite at £1,400, or the Rolls-Royce solution which adds 1080p resolution to the video, VBox HD, at £2,500.

Image of RaceChrono app

RaceChrono example screenshots

No question, this was far beyond what I was willing to pay, complete with specialised, doubtless very high quality hardware, one track day in. A bit more research turned up some phone-based solutions in Harry’s Laptimer and RaceChrono. Both appear to be apps built some time ago but still in development, and both get very good reviews. The difference seems to be Harry’s Laptimer is endlessly configurable and therefore difficult to master, and RaceChrono appeared to “just work”. On the strength of the reviews I read on various car-focused websites, and temped by the possibilities show in the marketing imagery like that above, I downloaded the free version of RaceChrono to dabble with.

I was pleased to discover the relatively niche Knockhill was available in the app in forward and reverse directions, and after playing with the app in my road car I really liked that it was possible to record a session using just the phone, including synchronisation of video taken from the phone’s camera if (and this was the hook) I was using the paid-for “Pro” version of the app. However, even in the free version of the app it enables data collection from additional sensors that either provide an upgrade on those in the phone or provide data otherwise not available, for example from the ECU via an OBD2 reader plugged into the car.

Data From the ECU

And so the tweaking and experimenting began. I decided to buy a cheap OBD2 reader from Amazon that would at least let me explore how the data from the ECU would be represented in the app for relatively little money – about £9. This opened my eyes to the wealth of information available from the ECU that the Caterham dials don’t communicate. Even if you have no interest in track days (and well done for reading this far if you don’t) I’d recommend you buy one of these cheap OBD2 readers to gain insight into what is going on in the engine: intake temperature, coolant temperature, revs, engine load, throttle position – even if only to verify what the dials are telling you. You can link the sensor to a free smartphone app called Torque, and see the data in dials and graphs in near-real-time. The whole experience is a little clunky, but does make a mockery of the £130+ specialist diagnostic sensors for the professional mechanic. It will also help diagnose a faulty sensor or more serious engine issue should you be unlucky enough to have one at some point. For £9 it is well worth it for the insight.

Synchronising Video with Data

I sprung for the Pro version of the RaceChrono app so I could experiment with video and in particular, synchronising and linking video from my GoPro Session camera which I already own and which I used at my first track day. RaceChronoPro is £17 at the time of writing, hugely expensive for an app, but this app does many clever things to deliver a quite professional end product and so I felt the purchase was good value for money. The app communicates with the external camera to tag the file name of the recording in the data, and the post-processing in the app allows the data and video to be synchronised easily. This means tidy overlays on the video which can be configured according to the data which you want to display.

More Accurate GPS

The GPS chip on my phone is used by the app to locate position on the track, and in particular when crossing the start-finish line to set a lap time. My phone (along with all others on the market as far as I can tell) updates GPS location at about 1 Hz – once per second. That’s fine for navigation in normal circumstances, but at 100 mph the car travels quite a long way in 1 second, meaning it introduces quite a margin of error when I’m looking to measure changes in lap times of tenths of a second. RaceChrono supports external GPS receivers and even recommends one in particular – the Garmin Glo at about £90. This uses two satellite GPS networks to locate itself (the usual, plus the Russian version) and has an accuracy of 1.5m. It also updates at up to 10 Hz, although in my experience this is something like 7 – 8 Hz depending on the satellite lock it is able to achieve in the real world – location in the car, weather, geographic location all affect the update rate. This is still good enough for me, giving me more confidence in those tenths of a second.

This is pretty much the limit of GPS positioning – at least that which is available for non-military purposes. More accuracy in terms of timing would come from fitting a transponder to the car and have a receiver track-side to clock it as it passes, but that’s very much not allowed for track days, as it is the method race teams use to time. It also wouldn’t give me track position and turn in points on the track map, so I’m happy this is the best I can do.

Testing on the road

I took a run out in my daily car with all my kit plugged in and connected to the app. Everything looked fine and I got video with overlay out of the post-processing in the app which looked great – I’d proven the linkage of video from the GoPro to the data from the OBD2 reader, the GPS, plus the phone’s own sensors. That’s a lot to bring together and it all “just worked” as per the reviews I’d seen of the app. There was an issue though – the data from the OBD2 reader was laggy. Somewhere between 1 and 2 seconds out, way too much to be happy with. After some digging, it turns out that the cheap ODB2 reader I bought has a refresh rate of 1Hz, just like the phone GPS. But more than this, the 1Hz is shared between fast path data channels.

ODB2 Data Channels

OBD2 data has two types of path out via the reader: slow paths and fast paths.  Fast paths should be used for rapidly changing data – revs, throttle position, engine load for example, and are updated at the maximum rate the reader can manage. Slow paths should be used for more stable data – coolant temperature, intake temperature, and thee are updated at less frequent intervals.

There are no restrictions on which measure can be placed on a fast or slow path, and so in my initial test I’d chucked about five measure on fast paths. It turns out that these fast path measures all share the update rate of 1 Hz, and so the engine revs, which was the one rapidly changing measure I chose to show on the overlay, was actually being updated at a rate of 0.2 Hz, and RaceChrono was interpolating data points between the real data points to smooth the data. Overall, this resulted in the laggy rev numbers I was seeing.

Upgraded OBD2 Reader

The recommended OBD2 reader for Racechrono is the ScanTool OBDLink LX because of it’s fast refresh rate of 30 – 40 Hz. There is also an MX version which is more expensive, and includes some specialist ECU data compatibility capabilities which are not useful in a Caterham, but which you may have a use for in another car. At £90, it’s ten times the price of the first reader, with the only significant difference being the refresh rate. However, it makes the video overlay of ECU data on the videos accurate and useful. There’s no discernable lag, even with 3 or 4 fast data channels in use and sharing the 30 Hz, and I can have any number of slow data channels in use without impacting the refresh rate. The data appears to be accurate, referencing the dials, and timely, and I really can’t fault the reader. It’s also much smaller and lighter than the £9 reader, so less chance of rattling around or bumping a knee while driving.

The end result

Future improvements

I’m really not happy with the sound on this video. A common issue with Caterham footage is the wind noise from the built-in mics on the cameras used to record it. Here my tiny GoPro Session 4 fails to cope sound-wise, but otherwise does a decent job. My next improvement to the kit will be a camera that will allow me to connect an external mic, plus of course the mic itself. I’ll need to experiment with mic positioning, but Robin’s results from positioning his mic in the passenger footwell, even with an aeroscreen, are impressive.

This also opens up the possibility of having front/rear facing cameras and using a bit of picture-in-picture, but I understand this requires a bit of manual handling of the video synching. I’ll try it and report back.

Spend so far

So here is my tally up of my spend so far in getting to a workable solution that produces a professional looking – if spoilt by wind noise – end product. For half the cost of the “basic” VBox laptimer I’ve got a system which allows me to incorporate track position, lap time, video with overlays of ECU outputs.

ComponentCost (£)
RaceChronoPro App17
Cheap OBD2 Reader9
ScanTool OBD2 Reader (LX)90
Garmin Glo GPS90
External mic20

The spend for the camera and mic are guesses for now. I’m confident I’ll be able to hit them though.

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