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      09-02-2020, 01:30 PM   #1
Blue2
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Are the BMW tire pressure sensors accurate?

The digital tire pressure readout in iDrive always reads lower than my tire gauge. Wondering which one is accurate.
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      09-02-2020, 01:43 PM   #2
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My gauge always shows a few psi higher than the TPMS does, and I go by my gauge instead of what the car says. All I use the TPMS for is to let me know if I'm below spec.
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      09-02-2020, 01:59 PM   #3
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I was concerned my TPMS was broken because it has showed the same reading consistently (when cold) since I bought my M2 in December. So I decided to recently check (I know, what was I thinking?) and the gauge showed the same, maybe 0.5 - 1 psi lower here and there. I then use a third gauge of measure, the electric air pump, to inflate up to 35 psi (which is my desired psi), and the air literally stopped filling within seconds. So, having triangulated all three sources of data, I'd say my TPMS was fairly spot on.
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      09-02-2020, 02:12 PM   #4
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Varies. Most are off 1 to 2 pounds. They seem to be fairly consistent among themselves.
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      09-03-2020, 06:05 AM   #5
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My TPMS is higher by 1 PSI than both my highly accurate gauges.
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      09-03-2020, 06:31 AM   #6
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My TPMS is lower by 1 PSI versus a tire gauge.
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      09-03-2020, 07:11 AM   #7
richard in NC
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I'd say mine is accurate to 1 PSI. I also had my tire gauges checked for accuracy. One was close 1-2 off, the other like 5 PSI off so don't use it any more...
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      09-03-2020, 10:15 AM   #8
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My TPMS always reads 2 pounds lower than gauges.
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      09-03-2020, 10:22 AM   #9
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Now I'm glad you started this thread, as I assumed they were all like mine. Weird that they are so inconsistent.
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      09-03-2020, 11:25 AM   #10
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My TPMS consistently reads ~1 psi low compared to my Longacre gauge and a cheap digital gauge that I have lying around.
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      09-03-2020, 11:41 AM   #11
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My TPMS is also about 2 psi lower than my gauge.
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      09-03-2020, 11:42 AM   #12
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This might seem like a silly question, have you tried to manually set the air pressure, then reset the TPMS sensor on the iDrive screen and see if that shakes out.
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      09-03-2020, 12:39 PM   #13
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Typically see TPMS measures it lower by 0.5 ~ 1 PSI.
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      09-03-2020, 01:16 PM   #14
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Quote:
Originally Posted by cncmastr View Post
This might seem like a silly question, have you tried to manually set the air pressure, then reset the TPMS sensor on the iDrive screen and see if that shakes out.
Yes... Unfortunately, the conditions were such that I learned nothing.

I set all tires at 37PSI and following the TPMS reset, they were all displaying exactly 35.0 +/- 0.1. So then my question became -- is TPMS actually measuring pressure, or just assuming a correct set-point (which it declares as "35") and then inferring pressures from temperature and rolling radius differences? I haven't had these tires off the rims yet. Are there actual pressure sensors on the M2?

I suppose i could let a few PSI out of one tire and reset to see what happens to the display?
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      09-03-2020, 01:42 PM   #15
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Worth a shot.
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      09-03-2020, 02:41 PM   #16
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TPMS seems to accurately measure the deltas. That's most important during track days. If it's 1-2 psi low cold, it will be similar when hot. The pressure and temp go up when in the sun, when driven hard, etc so it is real time measurements when driving. Older systems were rotational based to just warn if going flat but new systems do directly measure temp and pressure. Although I don't know why it insists on driving first.

During the latest autocross after a good many runs and as air temps went up, my psi increased from 35 psi to 41 psi. Temps hit 150 f. My tire gauge was close, 42 tops. I dropped all 4 tires 2-3 psi to regain traction.
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      09-03-2020, 03:27 PM   #17
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Quote:
Originally Posted by BlkSVT View Post
Yes... Unfortunately, the conditions were such that I learned nothing.

I set all tires at 37PSI and following the TPMS reset, they were all displaying exactly 35.0 +/- 0.1. So then my question became -- is TPMS actually measuring pressure, or just assuming a correct set-point (which it declares as "35") and then inferring pressures from temperature and rolling radius differences? I haven't had these tires off the rims yet. Are there actual pressure sensors on the M2?

I suppose i could let a few PSI out of one tire and reset to see what happens to the display?
That's weird, it definitley measures the pressure. I over inflate my winter tires by 3 PSI and when I do a reset it's reads the correct PSI. Did you by any chance inflate your tires when it was hot out and then did the reset in the morning or on a day when it was cooler outside?
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      09-04-2020, 12:56 PM   #18
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I cant speak for everyone's car but i can confirm that the TPS sensor probably reads about 1 PSI below what the actual PSI is. I used this fancy electronic machine to put all my tires to the recommended 35 psi. It blows air into the tire until it digitally reads the targeted setting. THen i was kind of speculating so i used my hand held analog reader and sure enough every tire was exactly at 35 psi. So then i checked the car, and it said 34 psi for all...
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      09-04-2020, 02:08 PM   #19
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I imagine the TPMS is set to read just a bit low because that's a common issue, especially as soon as it gets colder. Better to correct it early before increased tire wear and decreased performance sets in.
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      09-04-2020, 02:30 PM   #20
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I dont have my car yet so the recommended tire pressure on a 19" wheel for M2C is 35 psi, that high?
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      11-21-2020, 10:59 PM   #21
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Today I started a similar thread by mistake. Cross posting it here: https://f87.bimmerpost.com/forums/sh....php?t=1777005 .
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      11-22-2020, 02:25 PM   #22
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Yes our TPMS measures actual pressure and temp with in-wheel sensors. Older systems use wheel speed etc.

Coming from a measurement / instrumentation background I would say don't even worry about 2/3/4 psi difference at our pressures.

Even 5% accuracy over say 100psi is good for a home gauge considering temperature variation etc.

Fretting about 1 or 2psi is pointless to the extreme. What is more important is setting pressures with cool tyres and doing all 4 at the same time to get relative pressures correct.
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