You may recall some weeks ago I was singing the praises of Tyre Pressure Monitoring Systems, and suggesting that they should be made a compulsory install.
I must now confess to a weekend experimenting with the system after checking the pressures and discovering that one tyre was down 15 psi compared to the others. The system didn't notice (despite 300 miles of motorway driving the same day).
Further tests involving letting all the air out of the tyre (it's a run-flat) and driving carefully a mile up the road and back also failed to trigger a warning from the system. It was a careful test - I inflated the tyre, recalibrated the system, and then let the air out without stopping the engine to simulate, as best I could, a rapid and unexpected puncture while driving.
So either it doesn't work at all or any warning it does give you is far too late to do anything about it and save the tyre.
Last edited by: Alfa Floor on Wed 14 Sep 11 at 21:14
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Interesting - I check and calibrate mine as regularly as possible. The bike has a better system it provides real time pressures - I know these are accurate as they correspond with my old fashioned pressure gauge. I'll go dig out the car manual in a minute and see what it actually says - as opposed to what I thought it said.
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Manual tyre pressures do not always work either.
On the door opening of my new Xtrail (4 years ago) there is a list of tyre pressures for several models/tyre sizes.
llbs per sq in and BAR
Tyres looked a bit flat
Std Pressure for my model was 2.0 BAR, YEP they tyre was 20llbs/sq inch
Units of Measurement or rather wrong uses of units worry me - medicines say 20 ml might be written wrongly / dispensed as as 20 Cl (200ml). On the continent apparently doctors would prescribe in cl, UK ml
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Here is the thread.
www.car4play.com/forum/post/index.htm?t=7580&v=f
I feel that I stand vindicated in most that I said in that thread, with the possible exception of calling you a 'plonker' I now feel that you were merely taken in by the rubbish that is put about these days.
I am a firm believer in K.I.S.S. and regular manual checking of levels, pressures etc.
Last edited by: VxFan on Thu 15 Sep 11 at 02:12
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oh.... BTW the basic systems work not by PRESSURE monitoring, but use the wheel speed sensors, to measure the rolling diameter the the tyre - when a tyre loses pressure, the rolling diameter changes, thus the affected wheel revolves at a different speed to the others, putting up the warning.
It may be, that starting off with a low pressure, the system doesn't suss the problem as the rolling diameter doesn't change during the journey.
If so, the the system is worse than useless, as it gives the driver a false confidence that the pressure are all correct.....
Last edited by: swiss tony on Wed 14 Sep 11 at 21:49
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swiss tony, the use of the sensors is how I thought this worked on basic systems. So for run flats had assumed it would not be a basic system.
When I get my car in October I'll check how accurate it is - it displays pressures on the MFD display. And of course report (if I remember!).
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>> swiss tony, the use of the sensors is how I thought this worked on basic
>> systems. So for run flats had assumed it would not be a basic system.
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>> When I get my car in October I'll check how accurate it is - it
>> displays pressures on the MFD display. And of course report (if I remember!).
>>
IF the system reports pressures, then the wheel will have a pressure sensor built in, (normally at the base of the valve).
That system is worth having.
The basic system however, as I explained, isn't (in my opinion) worth a light.
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Yes it has a sensor on all 5 wheels. I paid the extra to have it. About £65 I think so costing me about £1 per month by my calculations.
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No sensor on my X1 - the manual describes how it works with measuring the rolling diameter of the wheel - once calibrated. The doesn't say much, but what it does say is that it can't measure a gradual loss of pressure from all four wheels, dunno when that would be likely to happen only maybe in winter. The bike's system is much more sophisticated (or so it seems) I'll dig out the manual tomorrow, but I know that the valve caps are critical items on the bike.
Last edited by: R.P. on Wed 14 Sep 11 at 22:36
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On the VWs with the standard TPMS there is a button to press near the gear stick to set pressures. I guess this is you checking all are okay and then telling the car to reset. Then loss of pressure (or increase?) is measured.
The valves on the car I have sitting nearby in the compound look like aluminium with a module inside the wheel. This measures pressures and is sent to the car's computer with pick ups in the wheel arches.
No idea how good/bad it is. But with self-sealing tyres when the car is new I didn't want to risk having a puncture and not knowing about it to be honest.
I assume the wheels are balanced to take into account the added weight of the sensor/valve. And when I get my first set of new tyres I am sure I'll keep nagging the tyre place to make sure they don't break it - which no doubt they will :-)
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The valves on the car I have sitting nearby in the compound look like aluminium with a module inside the wheel. This measures pressures and is sent to the car's computer with pick ups in the wheel arches.
Sounds like BMW Motorrad's system.
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I posted on another TPMS thread a link about VW's system on the Phaeton. I assume it's very similar for my Passat. From the graphics in the brochure it only shows pressures for the 4 wheels. The Phaeton system also monitors pressure (and temperatures of course) in the spare too. I assume mine will do the same but need to have the car to confirm.
Last edited by: rtj70 on Wed 14 Sep 11 at 22:55
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BMW 1-Series E82 coupe - TPMS - a confession - R.P.
