Quote:
Originally Posted by ALPINA_DREAMS
You can code a BMW to show you the real time tire temp in iDrive.
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TPMS location temperature is only a relative of tire carcass temperature. TPMS is a bulk temperature of the air inside the tire cavity along with the wheel temperature and is heavily influenced by brake heat input to the wheel structure (especially up front). Carcass tire temperature is a much different measurement, and this sensor allows capture of the continual transient temperature profile of the carcass itself right on the back side of the tread layer.
A simple heat transfer analysis will show how different measuring at these two locations are in a real time process. To put it in the simplest of terms (without delving into conduction, convection and radiation heat transfer needed to be accounted for in the analysis), it's analogous to measuring the temperature of the burner itself in a gas fireplace as the gas level is cycled higher and lower versus a room temperature sensor mounted 3 feet in front of the fireplace.
Whether said real time transient tread/carcass temperature is useful as used within the Michelin app or not is another question of course.
As to TPMS measured air pressures...at a recent time trial event on a very fast course that was about 82 seconds long, in the M2C I had the iDrive pressure and temperature screen displayed as I was curious how it would correspond to my measured pressure (I have both a Longacre and an Intercomp bourdon tube type gauge) after each run.
Due partly to massive heat input from the brakes, the pressures up front especially need to be constantly bled for at least the first four runs on course even when starting out low to begin with (31 psi). Anyway, immediately after the first run, the TPMS readout showed 32 psi LF and 34 psi RF, and get this with LF at 144F and RF at 145F; both started with exactly 31 psi measured and shown on the TPMS. My direct pressure measurement showed the LF at 37 psi and the RF at 38 psi (the course is somewhat biased to turning left, i.e. loading the RF the most).
After measuring them and readjusting to 34 psi for the next run (RE-71R btw), I checked the TPMS screen to see what it showed, and it was unchanged. Hence, not only was it way off on the pressure at the end of the first run, but even after the adjustment, it hadn't (yet) changed. I think there is some significant buffering in the pressure readout when it sees a wild change in temperature like occurs in this case where over 80 seconds time the TPMS location measured temperature went from about 75F to over 140F. I didn't bother looking at it for the rest of the event since I felt it was useless...direct, accurate pressure measurement immediately after each run was far more useful.