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I have a 2023 EQE 500 SUV with 19" wheels. (NOT AMG)
Observing the B-Pillar sticker, I want to inflate my tires to 280 kpa (40.6 psi)
I am at about 1 meter above sea level.
Using an accurate digital tire gauge, I fill all four tires to exactly 280 kpa (40.6 psi) according to my digital tire gauge.
But, my Mercedes Me app and the Service driver display, even after driving, continue to show:
Front Left: 280 kpa (40.6 psi)
Front Right: 280 kpa (40.6 psi)
Rear Left: 295 kpa (42,8 psi)
Rear Right: 290 kpa (42.1 psi)
How can this be? Could it be that the TPMS needs some sort of calibration?
If so, how is this done?
If calibration is allowed my guess would be only don via MB dealer tech computer gizmos....
now the Engineer geek it me will come out
The error for most tire pressure gages is 1% of max scale. (digital or mechanical) and is at soem standard temp and barometric pressure.
As temp and barometric pressure change so does the pressure inside tire and gage readings.
Tire pressure gages read GAGE PRESSURE (PSIg) which denotes pressure above atmospheric pressure.
So fill the on low pressure day when Hurrican is going by and they have lowest record barometric pressure and then check them when the record high front comes thru. (same temp) the tire will different Gage pressure.
Same as temp changes.
Note: PSIa or Absolute pressure includes Atmospheric pressure and is higher then PSIg- VEry rare pressure gage so donot worry.
For TPMS their atmosphere is complicated since they are inside the tire and the tire are inside the atmosphere your gage reads on valve stem.
So could read different if both were super accurae
Why do I bring this up?
It explains why measuring tire pressure can vary. lots of things affect what you measure and a difference of +/- 1-2% of pressure is not a big deal.
What is important is you use the same gage when measuring all 4 tires for refilling so left and right can be as close to the same as possible.
Now for the real tire pressure geek go get your gage certified.
Company will test gage and give you chart stating pressure indicated versus a certified pressure from certified pressure source.
Heck just getting people to agree on what is the optimum tire pressure is hard enough.
Thanks for the detailed explanation on this subject. It is far more complex than I had imagined!
My gauge packaging does not indicate any accuracy numbers. It wasn't a cheap gauge, but that still does not mean it's accurate. My variance, however, is far more than 1-2% from the TPMS reading on the rear wheels. I have no variance from TPMS on the front wheels.
This, while taking the pressures of all 4 "cold" wheels within a 5-minute span.
Until I've discussed with this the dealer, I think I will trust my tire gauge more than TPMS, at least for keeping the pressures on all four tires equal.
TPMS will still be useful to alert me about any extreme variances due to possible leaks.
yes I agree Fill tires using your trusted tire pressure gage,
The go to Tire Pressure menu reset - Now I do it with about 4 PSI less than what I eventually run so it so IT is not annoying.
Example my desired front pressure is say 36psi I fill to 32psi with my handy ASTRO Digital Tire pressure inflator (Matco Tools rebrands it for themsleves) Resolution: 0.1 PSI Accuracy: 0 - 58 psi: exceeds +/- 1.2 psi standard 59 - 174 psi: exceeds+/- 2.0 psi standard
Update:
After another 1 km drive, all TPMS pressures show the same pressure as my digital tire gauge. In the future, I guess I just need to drive a few km before I can expect accurate TPMS readings after adjusting tire pressure.
Bliss!
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