Hello Reader,

Question from reader

Should I use GPS for line analysis? I thought that would have been the main benefit of a GPS system but the lines are all over the place sometimes. It makes me wonder if the data is reliable? What's going on?

One of the great benefits of using GPS data for your driver analysis is that it knows where you are on track. That is ... until it doesn't.

Say you are wanting to compare lines through turn 3. You might be looking at a previous session you have done or you might have some data from a friend or team mate you want to compare.

You load the data into your analysis software. Pull up the GPS traces in a track map and ... disaster ... you've apparently been driving through a field!

There are several good engineering reasons why your data does not line up. The simple reason is that the satellites move through the day relative to you. The kind of consumer level GPS system that most have access to results in them thinking you were in a slight different place on the earth, each time you are on track. Luckily it does not really affect your data within your 30 minute track session. But it can make comparing line data from different sessions or systems "fiddly."

Simple check to see if you have good data

I do appreciate it can be unsettling when things that should line up don't. Whilst your data doesn't look right, it is probably fine.

Give yourself confidence your data is reliable by first looking at your lap times. If your times compare well with the circuit timing then your data is likely to be usable - even if the GPS lines seem off relative to the track map.

Video is more useful and more precise than the majority of consumer level GPS system for line analysis.

I personally avoid using GPS data for line analysis. If you have onboard video, use that instead. Not only does it give you more context to your data but can also help you spot more opportunities for taking a better line.

Hopefully using video also saves you a ton of time messing with GPS lines to see if you can align them or correct them in some way. You can in most software but for little return in my experience.

If you've only a basic video setup, or you are in a rush at the track, you can use this simple method to quickly create those side-by-side videos you see on the TV. In that link you also get to critique my driving - be kind 🤣

P.S. Are you following F1 testing this week and wondering what porpoising is all about?

I'm no aero guy but what I believe is happening is that, at speed, the shape of floor is sucking the car towards the ground... but then this abruptly stops.

On todays theme of video being a great medium to use, here is a video F1 shared of the Ferrari suffering porpoising:

Pretty uncomfortable looking right!

Called "ground effect" the aim with the shaped floor is to help the cars become less reliant on their wings for generating grip in corners. The hope is that that will mean the cars can run closer together for better racing.

The porpoising issue is that if the car gets too low, the ground effect abruptly stops in what my aero friends would call a stall.

No longer being sucked to the ground the car will lift up. At which point the air flow un-stalls or "re-attaches", and the car is sucked back down to the ground again ... until it stalls again ... etc.

This creates this very uncomfortable and unnerving looking effect people have labeled porpoising. It was also common last time F1 ran ground effect before it was banned.

Fascinating stuff and a subject I am pretty sure you are going to hear a lot about this year.

One last thing

Oh and I made the video play backwards as well as forwards on purpose.

I've found you can often pick up different things when the same visual is mirrored.

For me forwards, I was looking at the drivers head moving. Backwards, I was drawn to the visible gap under the car.

What did you pick up?

p.p.s. Your shares mean the world to me.

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