Tire Pressure Monitor System (OEM)

[Deek]

I have BMW's TPMS on my R1200RT. I have used a TireGard TPMS on other bikes, and the PSI indicated seemed very accurate and responsive; pressures indicated changed as I rode, generally about 5-7 psi after an hour or so. On BMW's system, the indicator on the dash seems to agree closely to the cold psi I get on a manual gauge before my rides, but then only changes a pound or two as I ride. I doubt the pressure is staying that steady.

 

Anyone else have this system and have any feedback for me?

Thanks.

 

[Guest Kakugo]

While waiting for someone more knowledgeable than me, it appears the BMW TPM has a certain capability for adjusting the displayed value according to external temperature.

 

For example if I leave home with a 7°C air temperature and an indicated tyre pressure of 2.4/2.8bar (36/42psi on my digital tyre gauge) it will stay that way all day unless temperature increases by over 10°C, in which case I will see 2.5/2.9bar displayed.

 

Since BMW (like all other bike manufacturers) recommends setting tyre pressure at cold, it only makes sense, or at least makes sense to me, they want the equivalent colt tyre pressure displayed to the rider.

[TestPilot]

Deek,

 

I'm not sure about the Camhead system, but the Hexhead system displays tire pressures corrected to 20C (68F). The sensors send both pressure and temperature to the RDC computer, and the computer makes the corrections for display on the instrument cluster.

 

The displayed readings will be close to actual when the tire is cold and the ambient temperature is near 68F, but after that the system's only real value is as a flat tire monitor system.

[na1g]

There is an explanation in the owner's manual. Unfortunately, the explanation is very poor at explaining.

 

But what's been said above is correct - the TPMS is temperature-corrected to a "normal" temperature, so as the tire and inflating air warm up during a ride, the pressures indicated have been adjusted to normal.

 

While this may make it simpler to monitor the pressures, it does not supply the information about how high the pressure actually get. This can be useful in determining the correct tire pressure settings and is used, I've been told, by racers and serious sport riders. Since I'm neither, the BMW TPMS works for me.

 

pete

[Deek]

Thanks for the replies. Makes sense. I actually like the way BMW has choosen to indicate the tire pressure...even though it looks odd to me until now. Since it's corrected for temperature, it's easy to tell is the correct amount of air is in the tires. And the TPMS on the Beemer does seem accurate, at least it's within a pound or two of what the manual gauge says.

 

[TestPilot]

Actually, BMW's system doesn't tell if the pressure is correct. On a colder morning, if the TPMS indicates the desired pressure, your tires are underinflated. I've seen no other system that works like this, automobile or motorcycle. It looks like another case of BMW's engineers trying to show the world how smart they are, but coming up well short.

[Paul In Australia]

Not so Karl

BMW indicates what the pressure WOULD BE at 68deg F

That is the recommended temp and pressure.

Regards

[TestPilot]

And what pressure does BMW recommend for bikes without TPMS? Do they recommend the owner apply a temperature correction to the published recommended pressures? No. So why be cute and do it with the computer?

[Paul In Australia]

Sorry, BMW recommended pressures are always temp controlled. The same as tire manufacturers are. A recommended pressure must be at a set pressure otherwise it is worthless. Boyles law. The TPM does it for you that's all.

regards

Paul

[Deek]

Sorry, BMW recommended pressures are always temp controlled. The same as tire manufacturers are. A recommended pressure must be at a set pressure otherwise it is worthless. Boyles law. The TPM does it for you that's all.

regards

Paul

 

Yep, although you meant "temperature" in the second sentence I believe. I sorta understand the other guys comments on the "cuteness" of BMW's solutions to some problems. They do seem to make things much more complicated than need be. My wife's 328 is that way, and all my RTs have had little quirks where you just have to ask "huh?".

 

But, now that I understand how the OEM TPMS is designed to work, I like it.

 

[texasaggie97]

I was wondering how do you make sure the TPM is correct? Why? I went on a trip this weekend and noticed my TPM PSI were down by 6 PSI from my last ride, So I pulled over and hooked up my tire gauge and the TPM was off by 6 PSI,both the front and back were off. I even purchased a new gauge to confirm my findings and it too was telling me the TPM was off by 6 PSI . How do you calibrate?

 

Thanks

[dirtrider]

Afternoon texasaggie97

 

To check your tire gauge against your TPM you need to have cold tires (like overnight cold).

 

Your TPM is temperature compensated so once you ride the bike a ways the TPM shows temperature compensated pressures that won't be the same as you non temp compensated tire gauge.

 

A lot of tire shops have a pressure gauge calibration set-up so you might see if you can stop by a tire store to check your gauge against a known pressure value.

 

[smiller]

BMW indicates what the pressure WOULD BE at 68deg F

But who cares what the tire pressure WOULD BE at standard temp? Taking this factor into account internally is a good feature on a TPMS system but displaying the corrected reading to the rider is not and causes the confusion expressed in the other posts. Just another strange 'this is the way we do it' from BMW. But at least other than that the system does work well.

[texasaggie97]

DR,

Thanks that makes sense. I added air and I could not figure out why it was constantly off. I will check the tire pressure tonight when I get home form work to see how it matches up. This could solve the problem.

 

Thanks for the advice I always know I can count of someone here to have a good answer.