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Technical Topics Wheels and Tires Just realized car dynamically adjusts recommended tire PSI based on temperature...

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      01-10-2021, 04:22 PM   #1
chenry
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Exclamation Just realized car dynamically adjusts recommended tire PSI based on temperature...

I haven't seen a thread on this before - if I missed it, let me know and I will delete this topic or fold it into the original thread

While I of course realize that tire pressure fluctuates based on temperature I did not realize that our cars take temperature variations into account and adjust recommended tire pressure accordingly.

Background:
  • I switched my tires from the oem run-flats to 255/35/19 go-flats
  • After install I went into idrive and manually entered the new tires
  • My new tire size was an option already in the idrive (see picture)
  • I enabled tire temperature using beemercode (maybe later models now have this standard? My car did not)
What I discovered (again new to me maybe not to you):
  • The car automatically adjusts the recommended tire pressure real time based on the current tire temperatures (see picture)
  • As an example: with front tires at avg. 89 degrees 42 PSI is recommend & with front tires at avg 97 degrees 46 is the recommended pressure
  • Same for rear (see pic)
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Last edited by chenry; 01-10-2021 at 04:26 PM.. Reason: messed up the bullets
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VipinLJ1936.50
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      01-10-2021, 04:49 PM   #2
VipinLJ
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Hehe I noticed that too when I switched from run-flats to non-RFTs.

Another thing I noticed is. My car ALWAYS shows a higher speed for a while before showing the speed it usually does (2MPH less than GPS speed). It happens after I select/change tyre options on the idrive and it resets the TPMS. It shows a 10% error for a while before correcting itself (I noticed it when I tried to do dragy runs and the speed it showed was 5-7MPH slower than the indicated speed). Not sure if it happens in all cars or only mine. You'll only notice it when you look at the GPS speed and indicated speed simultaneously (best method is by using cruise control). Like I mentioned before, not sure if it's only my car or if it's the same in other G20s. But it always happens in mine.

Edit - The "while" mentioned above is actually quite a few days/miles. When I first changed my tyre, it was around 600 miles. But in those 600 I miles, I kept fiddling with the settings once I noticed the error and it got the better of my OCD.
The second time I noticed it was after a message popped up a few days back on my idrive saying it detected a tyre change and I reset it again. The speedometer showed the same 5-7mph error but today, it was back to normal (2mph error). I've probably driven like 20-30 miles at most and 2-3 days since it happened (and I didn't fiddle with the iDrive this time around).
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Last edited by VipinLJ; 01-10-2021 at 05:21 PM..
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