Jusrt put some air in one of her Mokka's tyres (Mokka isn't on the menu) and tried resetting the system . . . . . .
Now the Octavia and the previous Passat you found the menu and pressed reset, it asked you if you were sure and that's it. It monitors whatever pressure you set the tyres to.
The Mokka asks you which of the three options the tyres are set to so no option to run the tyres slightly hard, will see if she is complaining when she comes back in, at least they are close to one of the options.
Are we heading for the situation where you have to use the manufacturers recommended pressures or the system keeps telling you off?
It seems the Octy is indirect and the Mokka direct . . you never stop learning
Last edited by: VxFan on Sat 23 Apr 16 at 17:21
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The Popemobile has a TPMS (indirect) but no pressure sensors. It is comparing rotation rates of the four wheels. If one deflates a bit, then its relative rotation rate goes up and the warning comes on. There is no way that it can tell what the pressures actually are. It works, it has come on once when one tyre was about 3 psi down, although it didn't say which one. It has held pressure ever since so it must have been a bit of grit in the valve or something.
The direct kind has the sensors. I guess those could be programmed to monitor absolute pressure and/or compare pressure between wheels.
The indirect kind seems good enough, and presumably uses the ABS sensor data so minimal hardware requirements. The pressure sensors are a pain by all accounts.
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>>It monitors whatever pressure you set the tyres to.
Most TPMS don't measure/monitor the pressure in the tyre. As already said, they are referred to as indirect TPMS and monitor wheel rotational speeds. The principe is that an under inflated tyre will have a smaller diameter. So pressing the reset button tells the car that the tyres are okay and it will report loss of pressure if the wheel rotational speed changes.
On my last car I went for the full tyre pressure monitoring system which would tell you the actual pressures in the small computer display between rev counter and speedometer. There was an option to say if you were using winter tyres. I went for this because the original tyres were self sealing and I thought one day I might miss a slow puncture. The option was only £120 I seem to recall so cost little in the scheme of things.
However, on the Passat it couldn't tell you the pressure in the spare wheel/tyre (no sensor near it) but the Phaeton tells you the pressure in all 5 wheels/tyres.
Last edited by: rtj70 on Sat 23 Apr 16 at 13:29
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The Mokka does say in the book that you have to install tyres with sensors or the warning light will be on all the time.
My issue with it is that it compares the actual with vx recommended and does not allow you to run in between the light load or the full load.
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>> My issue with it is that it compares the actual with vx recommended and does
>> not allow you to run in between the light load or the full load.
Yes, I take your point of course. But what logic is yours using when you tell it which option you have chosen?
e.g. -
- is it using that to recalibrate its own sensors? or
- is it going to report a pressure variance if it doesn't agree that your tyres are at the pressure you have selected?
or something else?
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>> Yes, I take your point of course. But what logic is yours using when you
>> tell it which option you have chosen?
Octavia - Indirect so i presume that it notes the relative rotational speed when reset and reports variances. I can set any pressure i like before pushing reset.
Mokka - the display asks you which setting you want (Light, eco, full load and these are the pressures on the sticker) so if you are a few lbs above (or below F/L) it may give you a warning all the time. There does not appear to be any way to set any other pressure.
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Actually I think it was full-load/part-load that the Passat had. But it displayed the actual pressures as well. The knew what the pressures should be and they were in the manual and on the filler flap.
In very cold weather pressures would drop quite a bit.
There must have been a fair degree of variance for low/high pressures because when you started driving the tyres were cold and would increase pressure as the air in them warmed up.
Last edited by: rtj70 on Sat 23 Apr 16 at 20:23
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Exactly, who knows what temp the default pressures have been set for, you have so many variables (temp, make of gauge, etc) that there must be quite a bit of variance in what is in the computer otherwise ir will be going off ALL the time.
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>> In very cold weather pressures would drop quite a bit.
Fairly straightforward to work out, assuming as an approximation that the volume of air in the tyre remains constant.
Pressure is proportional to temperature, not forgetting to add 273 to the temp in celsius and 1 bar to the tyre pressure readings, which are only measured relative to atmospheric.
Tyres set to 33psi at 25C would be at c. 29psi when the temperature is 0C.
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Some full pressure monitoring systems have a battery powered monitor inside the wheel. So to replace it, you have to take the tyre off. So if the battery life is less than the tyre life, going to get a bit expensive. OK for folk who do lots of miles and often need new tyres, but those of us who don't, and are sensible will either be running a car made before such things were compulsory or a car with a rotation speed based system.
Rotation speed systems should be very cheap, as the speed sensor is the ABS one, and all that is needed is a bit of software in the ECU. And that may have been there anyway, although I don't expect any manufacturer will admit it.
Last edited by: Slidingpillar on Sat 23 Apr 16 at 14:15
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The car I had three years ago had a rotation system-the car I currently have has a proper pressure monitoring system where you can set the pressures to what you are happy with and it will use them as baseline.The rotation system has certain failings-the tyres must be rotating for it to work and it must not be very sensitive otherwise it would flag up at every corner.
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>> it must not be very sensitive
>> otherwise it would flag up at every corner.
I don't think that is too much of an issue. Ours certainly picked up 2-3psi drop. A rolling average of say the last 10 200 metre segments would bring cornering time nearer to the calibrated mean and would enable earlier reporting of a faster drop in pressure than a smaller one, as compared with just measuring the last kilometre. The rear wheels travel a shorter distance than the fronts on average but that will be effectively aimed off for in the calibration, which I have been told takes several kilometres after pressing the button. Perhaps if you lived in Milton Keynes, and did the calibration on the M1, it might trip it up...
The handbook warns that changing one tyre or driving with more weight on one side will trigger the warning!
Ours has so far flagged no false positives - it has only triggered once, for that modest difference in pressure.
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Not sure how they work on the 3 Series - You get a nice pictogram on the display showing all four tyre pressures. They honked a warning one morning - re-set them at a Supermarket on the way in - no problem since. The bike uses tiny transmitters. They are accurate against a tyre pressure gauge...good reliable bits of kit.
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Soon-to-be-mandate flat tyre warning is not the same as TPMS.
TPMS is much better and gives temps but can be a PITA to maintain long-term. I prefer the former. Unlike VAG's TPMS (which I prefer), Renault's TPMS would warn you the tyre pressures are incorrect for motorway speeds 10 years ago, as they had pressures for city and motorway and just said 3PSI more fully laden to boot.
Last edited by: Shiny on Sun 24 Apr 16 at 20:10
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The Insignia had little sensors on the valves and showed the exact pressures, which I thought was great.
Newer TPMS are much more advanced and can do a deeper mathematical analysis on the ABS data allowing them to detect simultaneous under-inflation of all four tyres.
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>> Newer TPMS are much more advanced and can do a deeper mathematical analysis on the
>> ABS data allowing them to detect simultaneous under-inflation of all four tyres.
Why do they need to do that if they have the pressure at each wheel?
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I get the impression that systems based on pressure sensors are being superseded by what FF describes.
That shouldn't be difficult. Presumably the system can be calibrated at the factory to the radii and rotation rates that go with the recommended pressures, so it can alert the driver if it detects something radically different from that, especially if it can compare apparent speed at the wheels with true speed measured by its navigation system.
The LEC has only one standard wheel-tyre combination, so its fuel-flap diagram of pressures is wonderfully simple - as, presumably, is its pressure monitoring calibration. The chariot, in contrast, has about four. The one mine has is on the build sheet, so it could be in the computer too (probably needs to be for fuel and service calculations) but I imagine it's complicated by having run-flat tyres as well.
Last edited by: WillDeBeest on Mon 25 Apr 16 at 10:54
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Vauxhall - Tyre Pressure systems - Manatee
