While I appreciate the original OP's concern about the TPMS not agreeing with his personal pressure guage, unless there is a great difference, don't over think it. Firstly, unless you are a track day rider or racer, or very experienced rider, I doubt most riders would be able to tell if their tyres were 1 or 2 psi above or below the "recommended" pressure. Secondly, most off the shelf pressure guages are somewhat inaccurate. I have three and all give slightly different readings. I use only one regularly, and having found the front and rear pressures that suit me using that guage, that's what I use to set the pressures before riding. Thirdly, unless you have some very expensive equipment, the very act of removing the guage from the tyre probably recuces the psi in the tyre by about 1 psi. I feel that the TPM is more of a safety device. It lets you know that the pressures are in the ball park and will warn you if there is a sudden drop in pressure. Ride safe.

 

While I appreciate the original OP's concern about the TPMS not agreeing with his personal pressure guage, unless there is a great difference, don't over think it.

Well said. I keep my TPMS readings visible for the first day or so after a tire change. After that, I look at the reading only when filling up with gas.

It's a safety item to tell me if there's a catastrophic loss of air pressure. Nothing more.

Chris

 

The TPMS certainly proved its worth last year.
While returning from a rideout - about 30 miles from home - a TPMS alert for low pressure in the rear tyre.
Pulled into the nearest garage to check and apply a temp repair.
Unfortunately I could not locate the damage as the object was no longer in the tyre.
Leak was slow so pump it up and head home.
The TPMS made it possible to keep an eye on the presure. It need one more top-up at 14psi (approx 1 Bar) to make it home.
The damage (when eventually found! - it had to be immersed in water to find it) was too close to the edge for a permitted repair. It was also over three-quarters worn so time for a new one.
The TPMS alerted me to a problem and allowed me to monitor it.

 

Terror Australis. Most of the posters on this thread agree that the TPM's are really only good for letting the rider know that the tyre is losing pressure (not necessarily rapidly....just that it is below a predetermined level. I think about 4psi). During my 55 years of riding I've had two instant blowouts (one nearly fatal) and any number of slow leaks. Even the TPM will not save one from a blowout, but a warning that the pressure is getting on the low side (especially on a winding road) could well be the difference between arriving or not. If the batteries on mine go, I'll either replace the batteries or the whole unit.....just nice to know that that vague feeling round the last bend was due to road surface and not a soft tyre.

 

I'm not interested in the absolute measurment. There are onlt 2 that matter - the value cold when I check them before a ride and any rapid change while riding. I have experienced that with the warning coming up while doing 30mph through a village, just before a lenghy NSL section and several roundabouts.
I would rather see a flashy red light on the dash rather that a flashy blue light followed by a trip to A&E.

 

Bogbody. Nailed it (no pun intended!).

 

1 bar or 0.1 bar? The latter is 1.5 psi, how accurate is the pressure gauge you are using to check the tyres?

 

Could one or both of the TPMS batteries be on their way out? On some versions of the system the battery can be replaced and in newer versions, as used on my RS, the battery is potted in the device and the entire TPMS must be purchased directly from BMW. Then you need a franchised dealer to reset and calibrate the new TPMS equipment.

 

....the battery is potted in the device and the entire TPMS must be purchased directly from BMW

There are cheap clones available direct from China some have had no issues using these. Others have replaced the battery in the original TPMS by carefully cleaning out the potting material, soldering in a new battery and repotting (usually with hot glue gun)

..... Then you need a franchised dealer to reset and calibrate the new TPMS equipment.

New TPMS sensors can be coded with MotoScan app no need to take to dealers

 

Did you know the OE BMW TPMS fudges the pressure display according to temperature?

German We Know Better Than You Engineering has decided tire pressure should be set cold at about 20°C. So whatever your pressure really is, they display what they think it would be at the cold pressure. Perhaps I would not have noticed but for displayed pressure going down when tires warm. Caused me to measure with handheld gauge then remember the owners manual. Their pressure fudging is faulty, I’d rather have the unedited pressure. Also makes it difficult to add air to a hot tire, fill by the gauge or the TPMS? Teaches me not to trust the TPMS for an absolute answer, only a relative answer.

I have never seen TPMS pressure display change as battery wears. Doesn’t mean there isn’t a design which changes with battery condition. That I’ve seen a sensor which displays 35 PSI for 37 PSI according to my handheld gauge will always display 35 for 37 until the battery dies. Currently have one on my truck which displays 1 PSI lower than the other 3 when all set to the same with handhelds gauge.

 

Did you know the OE BMW TPMS fudges the pressure display according to temperature?

.......

Temperature compensation is codable in the BMW RDC unit.

 

The BMW TPMS system shows the absolute pressure in the tire adjusted not only to the temperature but also what it would be at sea level because the sensor sits inside the tire with no connection to the outside.

In contrast, your tire pressure gauge shows the tire pressure difference between the pressure inside the tire and the ambient air pressure outside the tire at your current location based on elevation.

Confusing?

Here's an example from 98lee in Pleasanton, CA at the BMW MOA forum:

Atmospheric pressure at sea level is 14.7psi.

Atmospheric pressure at 8000’ is 10.9psi.

14.7 - 10.9 = 3.8psi.

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

At sea level and 20°C (68°F) air temperature, the TMPS value and the value on your tire pressure gauge would be the same.

Your owner manual explains how to set your tire pressure correctly using a manual tire pressure gauge. In short, if the TPMS shows for example 1 PSI too low, you measure the current tire pressure and inflate the tire to 1 PSI higher than the reading from your tire pressure gauge.

And all that fuss because the BMW engineers want to show the correct absolute tire pressure INSIDE the tire which really counts.

 

And all that fuss because the BMW engineers want to show the correct absolute tire pressure INSIDE the tire which really counts.

No, the BMW "engineers" are regulating a constant mass of gas in the tire, not a constant absolute tire pressure.

Gauge pressure is the most correct measure for tire function. We need the difference between internal pressure and external pressure to maintain the structure and support of the tire. When temperature is 40°F the pressure will be lower in the tire than at 68°F unless additional air is added. The tire will flex more at the lower pressure. It will not behave in the way desired.

The correct "cold" tire pressure is set at ambient conditions. Then the tire will warm under use, pressures will rise to the expected values when smarter engineers determined the correct "cold" pressure.

 

We need the difference between internal pressure and external pressure to maintain the structure and support of the tire.

That is not correct! Changes in the ambient air pressure does not change the air pressure inside the tire. Same PSI inside the tire = same force on the inside of the tire to push the tire wall out. Now if the outside pressure changes by a lot, eventually the tire would deform. Like the tires on the Tesla car that SpaceX put in orbit.

That's why tire manufacturers use some rigid material within the rubbers of the tire to avoid the tire to bulge.

Yes, a temperature change inside the tire changes the tire pressure.

https://www.goodyear.com/en-US/learn/driving-tips/tire-pressure-cold-weather:

"For every 10 degrees of increased temperature, your tires can be expected to increase by 1-2 pounds of pressure."

 

Thank you for your input everyone. So, I was on a tour in the Switzerland and Austria riding the Alps which could explain why the reading was faulty. It was hot and I was at different sea levels.

I used quite a few pressure gauges at garages as I tried to figure out what was wrong. They all read similar pressures.

My bike is now home and I’m having a break so I’ll check my pressures when I return and update this post. I don’t think I said it was a 2014 model so batteries could well be on their way out.

Thanks again everyone. Rob

 

Hi Rob, in all honesty, I've had the TPMS in a 1200 and now the 800. Truthfully, all I've ever referred to it for, is as an alert for a rapid pressure drop, to give me an emergency warning. I've never bothered replacing the units or the batteries, although it's certainly possible, and many owners indeed have done so.
My go-to is to buy a DECENT pressure gauge, and check the pressures yourself, at cold, each ride.
TPMS for me are just farkles.
Cheers
Greg

 

I only agree that BMW's "We Know What Is Good For You" temperature compensated TPMS is only good as a relative indicator minute to minute.

"Cold" pressure is to be set at the current "cold" temperature. If it is 32°F and the tire needs 38 PSI then it won't have 38 PSI holding the tread in position using BMW's temperature compensated display. It will have the same number of moles no matter the temperature using temperature compensated pressure display. But that is not what a tire needs.

I know how much my non-compensated TPMS displays disagree with my hand-held pressure gauge. Rarely more than 1 PSI. Can reliably know "this one needs 3 PSI." Can't do that with the BMW.

 

I have read the compensation is set relative to 68F/20C but are we confident that is correct? Given the bike has an ambient air temperature sensor it would seem very easy to base the temperature compensation against this figure and not a constant which if I understand your posts correctly Dave should, in part, address your objections to the system.

Out of interest I did some checks this weekend, ambient temp was 18-20C, cold tyre pressure with gauge gave 35.5/42.5 (front/rear). Set off and TPMS showed 36/42 which changed to 37/43 for the next 2 hours of my ride (not fast mainly 30-50 mph in traffic) got back home and checked pressure hot and 38/46 with gauge. In this scenario I would say the temperature compensation has some worth but of course the ambient temperature was the same as the temperature that BMW are said to be using as their relative temperature. It may prove different if temperature was considerably colder.

When I get the time I'll attempt to code out the temperature compensation see if the code does what it says on the tin.

However all that said I'm in complete agreement with all those who believe TPMS is no substitute for regular manual tyre checks and the real benefit is alerting the rider to a change in pressure (puncture) before it's actually felt in the handling.

 

All good stuff being posted, thank you. An annoying issue for me was the screen would not move off the TPMS warning screen when riding. I wanted to see how many miles I’d done but it wouldn’t display. I later found this info on my SatNav but I may not always have that with me.

 

..............An annoying issue for me was the screen would not move off the TPMS warning screen when riding........

It's very simple to disable the TPMS in the Instrument Cluster via MotoScan app, you can leave all the other coding associated with TPMS alone it will not cause an issue. I had this during TPMS retro fit. My sensors where in the topbox waiting to be fitted to the wheels at next tyre change, the vibrations form riding would on occasion cause the sensor allocated to the front wheel to wake up and would then send a signal of 0psi to the bike and I got the alarm on the dash. I leave the cable and adapter in my topbox and MotoScan is on my phone so I could have done it at the side of the road next stop, which if on tour in the Alps is what I would have done as it happens I put up with it until I got home, then sorted it, after TPMS sensors fitted reactivated it in the Instrument Cluster and all worked fine.

Set the RDC K70 to "deactivated" and you get no TPMS information on the dash

 

FWIW the newer bikes with the TFTs allow you to disable the warning while still maintaining a readout. This is for people who do track days and air down their tires to the point that the warning would be on constantly.
So I don't think I've seen it mentioned yet, the temp that is being compensated for is not ambient, it's the air temp in the tire, as measured by the TPMS sender itself. This is because the pressure change we are concerned about is due to the tire heating up, not the day getting warmer. A rear tire will normally increase pressure about 20% if setup properly when at operating temp. Too low of a starting pressure will see a larger increase as the tire overheats and tire high of a pressure will do the opposite as the tire never reaches proper temp. Tire pressure isn't just about pressure, it's about getting the rubber up to operating temp while within a safe pressure range.

 

......the temp that is being compensated for is not ambient, it's the air temp in the tire, as measured by the TPMS sender itself.......

That was not in disagreement, it's what it is being compensated against that is under debate, the general consensus is a fixed 20C/68F, in which case N4HHE's argument holds true, if the ambient temperature is at the extremes at what we may ride in then the TPMS will compensate incorrectly.

 

I'd put my vote for STP as the basis for calibration barring any actual documentation.

 

A tool is only as good as the person using it.

 

Stop obsessing about this. Just check your tyres with your regular gauge, inflate (or deflate) to the recommended pressure and forget what the TPM says. Who really cares whether BMW compensates at sea level, on top of Mt.Evererest, the moon, or if the temp in the tyre is -3 or 100. If you really want to be anal, reduce the tyre pressure shown on the gauge by 1psi for every 5 degrees C below 20 degrees C ambient temperature, or raise it by 1psi for each 5 degrees C above 20C. As I said in an earlier post, I doubt that many riders could tell the difference of 1 or 2 psi above or below the recommended pressure.

 

For me, living at 6,500ft (2.000m), the presserure difference to sea level is -3.5 PSI. Any tour on the motorcycle is typically higher up.

Using a manual pressure gauge at my house, my tires would ALWAYS be under inflated by 3.5 PSI.

You low landers don't have that issue setting your tire pressure near sea level.

I invite you to take a trip up Pikes Peak and check your tire pressure with your manual pressure gauge. :shocked:

 

For me, living at 6,500ft (2.000m), the presserure difference to sea level is -3.5 PSI. Any tour on the motorcycle is typically higher up.

Using a manual pressure gauge at my house, my tires would ALWAYS be under inflated by 3.5 PSI.

You low landers don't have that issue setting your tire pressure near sea level.

I invite you to take a trip up Pikes Peak and check your tire pressure with your manual pressure gauge. :shocked:

Your tires would only be underinflated if you rode down to seal level. You wrongly assume the mass of air in your tires should be constant at all elevations. It is the difference in pressure between inside and outside that holds the tire in the proper shape, holds the motorcycle upright.

 

You wrongly assume the mass of air in your tires should be constant at all elevations.

It is! I am not assuming!

Btw. we are talking about VOLUME not MASS. As long as the tire doesn't have a leak and the tire has not bulged, the volume in the tire stays the same - no matter of the ambient pressure. Hence the pressure IN the tire stays the same.

 

Again we are diving off at tangents. Nowhere in any manual I've seen or owned (car or motorcycle) does it suggest changing/checking tyre pressures with a change in altitude. BMW may or may not have come up with some fancy algorithms for their TPM, but they haven't recommended checking one's pressure if one goes over, say, 2000m. I've no degree in physics, but if this was so important, someone would have said so by now.

 

The owner's manual for my 2017 F700GS explains excactly how to set up the tire pressure. First time I heard/read about this after so many miles on rubber tires.

If you use a tire pressure at elevations up to 2,000ft the pressure in the tire may be up to 1 PSI too low - not really significant. So maybe that's the reason this is not mentioned in a car/motorcycle manual?

There are lots of discussions like this one on the Internet which explains this much better than I can do.

 

A TMPS sensor inside the tire will not show that the tire is over inflated at altitude. External TPMS sensors may or may not indicate gauge pressure.

A handheld gauge is always the correct answer.

BMW's wont to "correct" the displayed pressure compensated for temperature is only correct at sea level and 68°F.

 

There are some really bad posts in this thread that are totally erroneous. I never thought that tire pressure could be so misunderstood. Take an empty drinking water bottle with the cap screwed on tight up in an aircraft and watch what happens. Unscrew the cap at altitude then screw it back on tight and check the bottle when you land.

Sent from my SM-T813 using Tapatalk

 

Perhaps people are overlooking that the TPMS may get readings of the pressure inside the tire from the sensor therein as well as barometric pressure from the BMSK's sensor.

Sent from my SM-T813 using Tapatalk

 

bmwroadsterca. Both points are valid. However I stand by my previous comment that BMW (and for that matter, every other vehicle manufacturer) feels that the affect on tyre pressure at altitude is so insignificant as to not mention it.