TPMS v cheap gauges v quality gauge

[Deman77]

Had really bumpy ride and TPMS readings off the charts after topping up my tyres with my usual upright hand pump with an analogue gauge (it was when temp dropped to single digits straight after the first heatwave in April, my TPMS complained - I did from what seemed like 2.0 to 2.4; it had warmed up since which adds about 0.1)
I was suspicious of the TPMS readings so I bought a PCL dedicated gauge that is calibrated to 1% and goes in 0.01 steps.
https://www.pclairtechnology.com/pro...-gauges/dtpg8/
I’ve done them to my recommended low load pressure of 2.40 per PCL. My original pump was showing 2.1ish, a new footpump showing 2.9ish and TPMS 240 (now TPMS only moves in increments of 10 so that’s +/-5) - still most accurate. What was shocking is the 25% range on the cheap analogue gauges - that’s just two I have: it could be much worse if I increased sample size.
Mine is the original hardware TPMS which they switched to software in MY17 and later models.

[gaby]

There is a possible reason for the difference between your digital gauge and the TPMS readings.
The reading of the TPMS system of my BMW motorcycle is always referenced to 20°C.
This means that you can always check/fill the tyres, no matter what temperature, the readings
show how much the pressure would be when "cold". I don't know if the Volvo system also
references to a fixed temperature, but if it does, then the readings will only be the same as
the ones on an external gauge if the latter is used to measure at this reference temperature.
You can check if Volvo shows absolute rather than relative (referenced) by looking at the readings with cold,
warm and hot tyres. If the readings stay about the same, then pressures are referenced to a fixed temperature.
If the readings go up as the tyres heat up, there is no compensation.
I don't doubt the quality of your digital gauge, but the site you link to mentions that it is self calibrating.
That would surprize me, more likely the gauge does an auto zero on start-up, but that is not auto calibration.

[Deman77]

PCL are some of the best you can get for accuracy and they are used commercially. I picked that one over mechanical because they quote tighter error on it than on the mechanical ones.
TPMS was accurate. The two cheap analogues were all over the place.

[gaby]

Originally Posted by Deman77

PCL are some of the best you can get for accuracy and they are used commercially. I picked that one over mechanical because they quote tighter error on it than on the mechanical ones.
TPMS was accurate. The two cheap analogues were all over the place.

"Cheap" and "accurate" don't often go together well
Accurate analog gauges do exist but are (very) expensive.
But it is a mistake (often made) to assume that digital is per definition more accurate.
Digital sensors have tolerances and uncertainties as well.
But they are much smaller, lighter and don't suffer from parallax errors.