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    TPMS- monitors rather than measures. Oh..., okay..., I guess

    This very-disappointing-for-the-perfectionist news came from PCA emailer:

    Question:
    The car's TPMS gives a cold reading different from two digital
    gauges. The TPMS' difference is 2.5 PSI compared to one gauge, and 4
    PSI compared to another gauge. I have no idea how to determine the
    exact accuracy of a gauge.
    Should I rely on the TPMS's number for a cold PSI reading, or go
    with the gauge that yields the closer reading?
    Answer:
    I would go with a guage than the system on the car. The system on
    the car is basically a monitoring system to alert you if you have a
    flat tire or are low on your tires. I would not use it to set tire
    pressures. The system might be a couple of pounds off if you want it
    right on the money.




    Re: TPMS- monitors rather than measures. Oh..., okay..., I guess

    I don't see a problem with that as whatever I pump them with, has an gauge built-in. This is much more practical than pumping, running around the car to read the preasure, running back to the wheel, give some more air, runninng ... (guess you get the idea).

    At the end, the value added by the option is a early warning when one looses air (or rather one tire). Guess there is a reason they call it Tire Pressure Monitoring System and not Tire Pressure Measuring System.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I have compared my TMPS cold tire readings versus gauges and they have always been spot on.

    Everytime the tires need more air, I fill them up and re-check that I reached the desired pressures with my own analog/digital gauges (its easier to just plug a guage to the tire while you are down there than having to look inside the car at the instrument panel back and fourth, besides the TMPS may a few seconds to do its job, its not as inmediate as the gauge).

    Then when I finish I check the TMPS reading and they have always been right on the mark.

    So once you have the coprrect tire pressures and you are on the road you can trust the readings of the TMPS.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I DEFINITELY use a separate tire pressure gage that has a full scale reading of 60 psi or a digitial tire gage WTH 0.1 psi increments (not 0.5 psi increments) and not the TPMS. I DO NOT rely on the air pressure gages that are built into the air line chuck. They are OK for the approx. pressure.

    When outdoor temperatures require, I usually overfill my tires a few psi at home (I have an air compressor) and when they are cool (usually over night), I bleed them to the correct pressures. My presure gage (home made) has a small air bleed hole that I just hold my finger over to seal while I'm taking measurements. There are many commercially available precision tire pressure gauges that have a tire air bleed feature.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I thought TPMS was probably a worthwhile option ......... only to find that Porsche don't recommend it for cars in summer temps over 40deg ........hence a standard delete item for the dealer here. No bad thing to get the gauge out regularly !

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Hey Guys, don't get me wrong. It is still great to have this important system.

    What bugs me is it's apparently giving NUMBERS that are INACCURATE. Sooooo, one might ask why give the numbers at all? Scheesch.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Becuse they ARE accurate, at least thats my verified personal experience.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    If you think its inaccurate take it to the dealer for calibration

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    <Becuse they ARE accurate, at least thats my verified personal experience.>

    agreed. mine are dead on against a digital gauge

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    From my experience TPMS is 1 PSI lower than what the filling stations air pumps say. That may be because I've only compared the pressures in 2 stations thus far, so certainly could be inaccuracies in the stations equipment and not the TPMS.

    After I had my rear tire blow-out the other week (for which TPMS was an absolutely god-send by the way) Porsche set the new tire on the full 40psi when cold. This then didn't match any of the other tires as it was too high when warm. So I went to my local garage and set them all at the following whilst they were still warm from being on the motorway:

    Front L/R: 34 34
    Rear L/R: 40 40

    (Note, this is the TPMS reading, the air pump reading was 1 PSI higher on all)

    When cold these now start at:

    Front L/R: 30 30
    Rear L/R: 36 36

    ...and take about 10 minutes to fully warm up (great for knowing when you can really start throwing the car into corners!)

    I do occasionally notice that one of the tires will go randomly down by 2 PSI compared to the other equivalent tire. This normally corrects itself within 60 secs or so and goes back to normal (thank goodness!).

    My personal opinion is that TPMS is an absolute must have option.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I played amature scientist yesterday. Using a non-cheap electronic guage:

    cold

    TPMS indicates 31 37

    Guage indicates 34.5 40


    Hot:

    TPMS indicates 36 42
    guage indicates 38 43.5


    differences of 3.5, 3.0 (cold) and 2.0 , 1.5 (hot).


    This seems a bit messy for what I expected from TPMS.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Talk to your dealer about that. Mine are always spot on.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    Carlos from Spain said:
    Talk to your dealer about that. Mine are always spot on.



    Will do. Thanks Carlos for the reference point.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    MMD,

    I'm getting results somewhat similar to yours. TPMS gives lower readings, after I have inflated and checked the pressure (cold) with a mechanical gauge (not electronic). The difference varies between 2-3 psi. And I checked this against a different mechanical gauge that I have, and the results were the same.

    As long as the TPMS actually warns me when the pressure is too low!! Then I can stop and check the tires before damaging one of the wheels.

    Jim

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Doesn't Porsche give you a VDO tire pressure gauge as part of the delivery kit? They used to. That's what I would use to check the TPMS.

    dan

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    Jim48 said:

    As long as the TPMS actually warns me when the pressure is too low!!



    Yeah..., I guess..., definitely 1000x better than nothing. I was hoping for accurate numbers. . Now I gotta get mine checked out. Ours is nicer than BMW's though; since BMW relies on different rotational speeds to detect low air situations and indicates problems by a fault light on dash. I would imagine our system will give a much-appreciated warning first.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I'd rather have a spare. I've had 3 flats over three years of daily driving.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    MMD said:
    I would imagine our system will give a much-appreciated warning first.



    Oh it does, my rear tire was completely flat after about 2 minutes when I had mine go the other day. TPMS gave me plenty of warning as soon as it started to go. Way before I felt any instability in the cars handling.

    I managed to slow down from 60mph (ish!) and pull straight over into a lay-by. I then got out and watched the tire go all the way down. No wheel damage done at all and, more importantly, me not wrapped around a tree!

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    MMD said:
    Quote:
    Jim48 said:

    As long as the TPMS actually warns me when the pressure is too low!!



    Yeah..., I guess..., definitely 1000x better than nothing. I was hoping for accurate numbers. . Now I gotta get mine checked out. Ours is nicer than BMW's though; since BMW relies on different rotational speeds to detect low air situations and indicates problems by a fault light on dash. I would imagine our system will give a much-appreciated warning first.



    MMD,

    I'm going to have mine checked out, too. Sometimes the readings are erratic, that is, not consistent with what they should be given the outdoor temperatures and given that I check the air pressure (again, cold) before going out for a ride.

    I can only think of two other things that may be the source of the problem: 1) I washed it last Friday, and the readings have been goofier since then; and/or, 2) I've got Continentals as tires. Is it possible that there's a difference in the readings due to the tire's composition - different expansion because of a different rubber compound?

    I can't think of any other reason, unless the TPMS sensors are defective.

    Jim

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    I just got back from my dealer. They deflated the tires to 2.3/2.7 according to an analog gauge and TPMS instatnly gave an 'add air' message with a -0.3 deficit.

    After driving for a while, TPMS is still unhappy with the pressure. So the dealer told me that the TPMS needs to be re-calibrated, which is a 2-3 hour job. I opted to take the car out of the workshop rather than wait.

    The top engineer tells me that he faced the exact same problem with a Carrera GT TPMS, and that the only solution is to re-calibrate TPMS.

    Sounds odd to me, but I'll re-measure using my own (expensive) gauage early in the morning before driving to know whether TPMS requires re-calibration. Can't understand it though.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    Oxonian said:
    the TPMS needs to be re-calibrated, which is a 2-3 hour job.



    Wow. Seems like an absurd amount of time for something so simple.

    Maybe it would be easier/faster to add error to "recalibrate" our handheld guages so they match whatever the TPMS says!!!

    Thanks for getting to the bottom of this Oxonian.

    Re: TPMS- monitors rather than measures. Oh..., okay..., I g

    Quote:
    MMD said:
    Quote:
    Oxonian said:
    the TPMS needs to be re-calibrated, which is a 2-3 hour job.



    Wow. Seems like an absurd amount of time for something so simple.

    Maybe it would be easier/faster to add error to "recalibrate" our handheld guages so they match whatever the TPMS says!!!

    Thanks for getting to the bottom of this Oxonian.



    I guess I'll have to use my gauge frequently to check the pressure before I go out for a ride. I'll get the dealer to recalibrate it when I go in for an oil and filter change.

    Jim

     
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