Highly inaccurate TPMS readings - dealer says no fix

wbrownell9 said:

Yes, BMW corrects the pressure sensed by the TPMS to 68 degrees, but I'm not convinced that does anything useful... then monitor the TPMS for changes. The actual number doesn't really concern me, it's a change that I worry about.

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It absolutely does something useful, and you said it yourself, twice. If you got the actual number instead of temp-compensated, you would need to do some impressive math to figure out what was happening. My best example of this was from a trip in 2016 where we left Big Pine, California at 50F, and then proceeded to ride past Las Vegas on June 5th to St George Utah, and temp for the last 2 hours of that was 112F. TPMS on my '16 R1200RT did not waver at all for the entire day, nor any other days for that matter. If you had watched realtime actual temperature in that incredible heat, uncompensated, would have to do some tricky math in your head at highway speeds to ascertain what was actually happening. Temp-compensated if fabulous and absolutely what is needed if you are...'monitoring TPMS for changes'.

As a side point I count on reported TPMS temps exclusively. Why? There is absolutely no reason to believe my $50 Flaig guage is somehow superior to directly sensed tire pressures. Moreover, BMW actually suggests you adjust to your TPMS readout, not the other way around. After the tire is road-warmed, I can count on TPMS reported temp-compensated pressure being 2 psi lower than what my Flaig says. My tire pump actually correlates perfectly w/ TPMS, but my expensive German main analog Flaig gauge differs by 2psi. Which one is accurate? Don't have a way to calibrate and further, it really doesn't matter. I learned that when the Michelin Rep said to deal w/ severe cupping w/ the wretched PR4GT the solution was to raise the front tire PSI from 36 to 40. Oh, okay I see. Put another way, a few PSI hardly matters, IMO.

brownie0486 said:

I know people don't agree with the above pressure changes based on ambient temps. I set the pressure on cold tires in the morning before riding off for the day based on temp chart off the recommended pressure chart off the 68F recommended settings by manu's.

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I also use the temp chart when airing our tires.
I can go a couple weeks on a trip without messing with the tires.
I just look at the TPM reading every day or two. Now that we have intercoms I can ask Debbie what her pressures are when we take off in the morning.

For what ever it is worth, I just got back fro a trip out west on my 2018 RT. I aired up the tires at 900 feet and maybe 75 degrees. I traveled over 10,000 feet in elevation. I would just check the pressure read out on the TFT when starting out in the morning and once at close to 10,000 feet just to see. The bike's information never varied more than a couple PSI. I never checked the pressures with a gauge during the trip.

PoorUB said:

I never checked the pressures with a gauge during the trip.

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That's really the thing: you DID check pressures with a direct-sensing gauge, continuously, eliminating operator error in sealing a simple pressure gauge to the valve stem. It blows my mind people think their $30 gauge, manually applied, actually is more trustworthy than the wonderfully sophisticated direct sensing system BMW employs, and temperature-compensating at that, and moreover it's actually sensing tire air pressure at that. It's as good as it gets.

98lee said:

It is not only relavant, it is the entire reason that your TPM and your gauge don’t match.

Most TPMs, since they are enclosed in the pressure that they are reading, read in PSIA (or Absolute). Their reading does not change much with change in atmospheric pressure.

Virtually all tire gauges are differential gauges that measure pressure differential above an assumed 14.7 psi (atmospheric pressure at sea level. They will vary depending on what altitude you are testing the tire pressure at.


Atmospheric pressure at sea level is 14.7psi.

Atmospheric pressure at 8000’ is 10.9psi.

14.7 - 10.9 = 3.8psi. Does that number ring a bell?

Your differential tire pressure gauge is reading 3.8psi low because it is assuming 14.7psi atmospheric pressure when you only have 10.9.

Generally TPMs aren’t intended to be accurate enough to SET your tire pressures with. They are intended to warn you when things get out of whack while you’re riding.

If your spending all your time at 8000’, set your pressures 3.8psi higher than recommended with your gauge, see what your TPM reads, and go have fun.


Or set your pressures with your gauge to where your bike feels best and realize the numbers on your TPS might not match your gauge and use the TPS monitor to warn of notable change (lower).

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Thanks for the info. That's really good to know.

To add in my 2 cents, I've never been a big fan of the built in TPMS (and I could care less about temp compensation).

I've been using FOBO valve cap mounted tire monitors for about 4 years now and absolutely love them. I can check my pressure from the couch inside my house and know if I need to top it off before a ride. I ride with my phone mounted so any loss in pressure triggers the app to alarm and it lets me know immediately. They are pretty spot-on accurate as well and the new version is very compact. I highly recommend them to anyone.

truckerdave said:

You know, i wondered for a while why my new used K1300GT had everything on it you could get............except for the TPMS system. After reading of some of the problems and the godawful replacement part costs, i believe someone knew what they were doing by not getting TPMS. An air gauge works just fine, and a lot cheaper.

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My older brother talked like you and had 750K miles on motorcycles, but once he had TPMS he said he couldn't believe he lived w/o it. Your air gauge is worthless when, as I did, you're about to enter a high speed freeway, on the onramp accelerating hard and about to enter traffic, when the alarm goes off detecting pressure loss. Pulled over before entering the freeway and repaired the flat, and went on my merry way. I've had no problems in either BMW owned that had TPMS for the last 7 years. I keep pressures visible on the MFD on my '16 RT and it's very reassuring to enter curves fast w/ full confidence your tire pressures are spot on. When you're traveling 100 feet per second, seconds matter. Wouldn't want a bike w/o TPMS now.

Yep, my buddy just had a flat on his Harley. He is pretty OCD and he said he checked the air pressures in the morning before he left, and I believe him. I have seen him check air pressures multiple times a day. How many of us check it once a day? Anyway he was running down a four lane and the bike got squirely. He slowed way down and rode a short distance to a safe place to pull off and checked and the rear tire was flat with a large screw in it. TPMS would have caught it sooner and he probably wouldn't have been running 70 MPH with a flat.