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Thread: Tire Pressures (and pressure sensors)

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    Tire Pressures (and pressure sensors)

    My manual says tire pressure is to be set at 2.5/2.9 bar. I find it weird that the rear pressure is not dependent on whether I'm solo or two-up, but OK, I assume BMW know what they are doing.
    The manual also says that the tire pressure monitoring system is "temperature compensated" and seems to say that the reading from the sensor will not change even though the pressure in the tire changes as it heats up and cools down. Ok so far.

    However, the sensor readings DO change a bit from time to time as I ride - typically one or both tires will increase .1 bar to 2.6 / 3.0

    So, am I supposed to set the pressure correctly when the tires are cool/cold and ignore the increased readings when riding? Or am I supposed to bleed off some air when either sensor reads high to bring it back down to the recommended level?

    How accurate are the sensors?

    Bob

    2014 R1200RT

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    Kool Aid Dispenser! jimvonbaden's Avatar
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    Set them cold.

    The TPS is designed to give you and indication of issues, not exact tire pressures at all temps. That said, cold, mine are spot on with my tire gage!

    Jim

  3. #3
    Cold. The temperature correction algorithm, and the measurement of temperature don't seem to be perfect. Use it for its best feature - the alarm notification. Don't get lost in the noise level.
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    Registered User mneblett's Avatar
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    +1

    The BMW TPS system is notable for the fact that unless your tires are at 68F (20C), it reports a *wrong* pressure value. Basically useless except for indication of a significant pressure loss in a relatively short time.

    As described in the manual, the system takes whatever pressure it is reading and the temperature and tells you what the pressure would be if the tire temperature was 68F. Given that tire pressure decreases at roughly 1 psi/10F, that means that if you relied on the TPS read out when it was 38F, the actual pressure in your tires would be 3 psi low. Same at 98F -- your tires would be 3 psi over-inflated.

    Bottom line, use your tire gauge and measure actual pressure, and ignore the TPS for anything other than "oh cr@p, a leak!" indication.

    p.s. -- the BMWs I've had with TPS have never agreed with my several gauges. It is entirely possible that all of my gauges read 2 psi too high and the TPS on my R12RTW is correct, but I'll put my money on the TPS sensors not being particularly accurate.
    Mark Neblett
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    Quote Originally Posted by bobs_one View Post
    My manual says tire pressure is to be set at 2.5/2.9 bar. I find it weird that the rear pressure is not dependent on whether I'm solo or two-up, but OK, I assume BMW know what they are doing......

    2014 R1200RT

    I question this as well. My hunch is it could be a problem with TPS if they would spec two different pressures such as 33-36 (one-up), and 36-42 (two-up). Does TPS flash a warning when rear tire pressure is 35? What is it 1 pound low or 7 pounds low? BMW could spec one-up and 2-up pressures with TPS if they integrated ESA suspension setting to the TPS. Or by allowing us to set the TPS to whatever pressure we choose (with a limit say 30 as a low).
    14 R1200GSA, 93 R100R, 15 FJ-09, 15 Road King, 07 Moto Guzzi Griso No car is as fun to drive as any motorcycle is to ride.

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    Small road corner junkie pffog's Avatar
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    Quote Originally Posted by milo View Post
    ................... Or by allowing us to set the TPS to whatever pressure we choose (with a limit say 30 as a low).
    This would be helpful, for those of us that like to have a spirited ride in the twisty stuff.

    Aside from that there is NO correct tire pressure. The "ideal" pressure varies with tire model, load, riding style etc. In reality anything between 30 and the max recommended on the carcass will work 99% of the time.
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    Kool Aid Dispenser! jimvonbaden's Avatar
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    Quote Originally Posted by mneblett View Post
    +1

    The BMW TPS system is notable for the fact that unless your tires are at 68F (20C), it reports a *wrong* pressure value. Basically useless except for indication of a significant pressure loss in a relatively short time.

    As described in the manual, the system takes whatever pressure it is reading and the temperature and tells you what the pressure would be if the tire temperature was 68F. Given that tire pressure decreases at roughly 1 psi/10F, that means that if you relied on the TPS read out when it was 38F, the actual pressure in your tires would be 3 psi low. Same at 98F -- your tires would be 3 psi over-inflated.

    Bottom line, use your tire gauge and measure actual pressure, and ignore the TPS for anything other than "oh cr@p, a leak!" indication.

    p.s. -- the BMWs I've had with TPS have never agreed with my several gauges. It is entirely possible that all of my gauges read 2 psi too high and the TPS on my R12RTW is correct, but I'll put my money on the TPS sensors not being particularly accurate.
    Interesting observation. My TPS has always been within 1 pound of my several gauges cold. I do not worry about a couple of pounds one way or the other. I am not a racer and can't tell the difference anyhow!

    Jim

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    Registered User ItsPhilD's Avatar
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    Bought my 2008 RT used and it did not come with TPS. I purchased a Garmin Zumo 390 and use their valve stem cap TPS system. Batteries are replaceable and the readout gives you a true pressure reading which increases as the tires heat up. I think I prefer this over BMW's static readout system.

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    So, I'm in Phoenix, I air my tires up to spec 3 gauges agree my tps reads 3psi low (it's 100degrees out), the only time I get an alarm is when I air my tires down to 25 psi to go of road. I ignore the tps and just go old school check at coolest ambient and ride.

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    Registered User ItsPhilD's Avatar
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    Quote Originally Posted by mwlust49 View Post
    So, I'm in Phoenix, I air my tires up to spec 3 gauges agree my tps reads 3psi low (it's 100degrees out), the only time I get an alarm is when I air my tires down to 25 psi to go of road. I ignore the tps and just go old school check at coolest ambient and ride.
    I'm in Phoenix as well. Had the BMW factory TPS on 2 previous bikes and really prefer the Garmin.

  11. #11
    Quote Originally Posted by mwlust49 View Post
    So, I'm in Phoenix, I air my tires up to spec 3 gauges agree my tps reads 3psi low (it's 100degrees out), the only time I get an alarm is when I air my tires down to 25 psi to go of road. I ignore the tps and just go old school check at coolest ambient and ride.
    Of course. You aired to spec but were at 100 instead of 68 (20C) so in fact were 3 psi low. At 100 the pressure should have been +- 3 psi higher than cold spec.
    Paul Glaves - "Big Bend", Texas U.S.A
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    Registered User mneblett's Avatar
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    Quote Originally Posted by PGlaves View Post
    Of course. You aired to spec but were at 100 instead of 68 (20C) so in fact were 3 psi low. At 100 the pressure should have been +- 3 psi higher than cold spec.
    Alternatively stated, you set the correct pressure at 100F, but the TPS converts it to 68F, meaning it subtracts 3 psi (98F-68F = 30F x 1 psi/10F = 3 psi).

    Bottom line, tires are set correctly at 100F temp, but the TPS displays the "wrong" pressure (corrected instead of actual). BMW could hardly have made what could have been a very useful actual pressure display into a more useless display for anything other than gross pressure loss warning.
    Mark Neblett
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    Small road corner junkie pffog's Avatar
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    If it didn't show compensated pressure, many of the ODC anal retentive riders would constantly be stopping constantly to adjust the pressure. A few years ago someone on this board was concerned he would be in the Rockies and wanted to know at what elevations he should deflate and re-inflate his tires.



    I do agree, just a low pressure light would be sufficient for safety purposes.
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