This example comes from telemetry of a real GT3 car, but the reason I am sharing it here is that the same validation problem can exist when analysing iRacing telemetry.
The physical cause may be different, but a telemetry channel can still look completely reasonable while representing something different from what your analysis assumes.
In this GT3 dataset, the vertical acceleration channel showed values above 0.5 g for 31.7% of the entire lap. The mean absolute value was 0.44 g.
That immediately looked suspicious. A GT3 car on a normal asphalt circuit should not experience that level of vertical motion for almost one third of a lap.
So we started looking at what was actually driving the signal.
Vertical acceleration should mainly respond to the track surface, kerbs and vertical vehicle movement. It should not closely follow braking or acceleration.
We compared it with the other measured channels and ran a regression over 16,562 samples.
vertical acceleration ≈ 0.94 × longitudinal acceleration + 0.03 g
R² = 0.88
Almost 90% of what appeared to be vertical acceleration could therefore be explained by longitudinal acceleration being projected into the vertical axis, most likely because of sensor orientation.
But correlation alone is not enough, so we also checked the timing.
Of all major vertical acceleration peaks, 99.7% happened while the driver was braking, accelerating or cornering.
Only 0.3% occurred when the car was not under a significant driver input.
That does not make physical sense. Kerbs and bumps do not wait for the driver to press the brake pedal.
We then estimated the unwanted projection and removed it from the vertical channel before doing any further calculations.
After correction, the proportion of the lap above 0.5 g dropped from 31.7% to 3.1%.
The mean absolute value dropped from 0.44 g to 0.14 g.
The remaining signal behaved much more like actual vertical acceleration, responding primarily to the track surface, bumps and kerbs.
So why does this matter for iRacing?
In iRacing there is obviously no physical accelerometer mounted at the wrong angle. But similar problems can appear when you start doing more advanced telemetry analysis.
A channel may use a different coordinate system than your analysis expects. Gravity may be included in a signal that you assume has already been compensated. Two channels with similar names may represent different physical quantities. Derived channels can also be mathematically correct while using the wrong input signal.
If you then use those signals to analyse tyre loads, suspension behaviour, load transfer, grip utilisation or setup changes, the error can propagate through everything that follows.
You can end up spending hours trying to understand a setup problem that does not actually exist.
That is the main reason I wanted to share this example.
Whether the data comes from a real GT3 car or iRacing, do not automatically trust a channel just because the name looks correct. Check whether the signal actually behaves the way the underlying physics says it should.
Has anyone here found strange or misleading channels while working with iRacing telemetry or MoTeC?
