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Tyre pressure

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brightncheerful
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Tyre pressure

#441823

Postby brightncheerful » September 13th, 2021, 10:43 am

Skoda Octavia has a tyre pressure monitor where after I have manually changed /checked the existing pressures to as they should be I confirm to Octavia that the pressure is correct.

What happens then? Does a warning only arise if the pressure in one (two, to three, or all four) of the tyres differs from the saved setting, or is it down to me to check the tyre pressures manually? Only last week whilst i was driving I sensed the tyres needed checking and when i did they were all 1-1.1.25 bar lower than I had told Octavia the Octavia monitor hadn't warned of anything amiss.

Just searched on-line: the monitor is to warn it when at least one tyre is insufficiently inflated in comparison to the stored value in the system computer. So really it is not about whether the tyres need checking generally but whether any of the tyres is insufficiently inflated. In which case, is there a bracket, or permitted margin, before a tyre becomes insufficiently inflated in comparison?

Usually i check the pressures every couple of weeks, depending upon the external temperature. Exception is for heavy load carrying.

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Re: Tyre pressure

#441831

Postby servodude » September 13th, 2021, 11:11 am

brightncheerful wrote:In which case, is there a bracket, or permitted margin, before a tyre becomes insufficiently inflated in comparison?


Yes. There ain't a control system known to man that works on "exact values".

The warning threshold will probably be set to just before the measured value becomes a problem
- when you let it know the values are correct you're really just calibrating the sensor
What you're doing with regular checks is exactly what you should be doing (consider that like adjusting the gas at the cooker and the sensor/warning being more a smoke alarm)

-sd

swill453
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Re: Tyre pressure

#441835

Postby swill453 » September 13th, 2021, 11:26 am

Obviously I don't know how your Octavia does it, but my VW tyre pressure monitor doesn't physically monitor the air pressure. It measures the relative speed of all the wheels using the ABS sensors, and flags up discrepancies as tyre pressure loss.

If all 4 wheels have dropped at a constant rate it may not pick it up.

Tyre pressures vary at temperature and should usually be measured cold, so the discrepancy you noted may be normal.

Scott.

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Re: Tyre pressure

#441844

Postby bungeejumper » September 13th, 2021, 11:44 am

swill453 wrote:Obviously I don't know how your Octavia does it, but my VW tyre pressure monitor doesn't physically monitor the air pressure. It measures the relative speed of all the wheels using the ABS sensors, and flags up discrepancies as tyre pressure loss.

That's intriguing. Sounds simpler than the usual valve sensors, but how does it cope with normal tyre wear, which will also cause divergent rotation speeds? Does it scream foul play if you fit a new (i.e. bigger) tyre, or maybe a slimline spare - which can quite legally have a smaller circumference than the other three?

BJ

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Re: Tyre pressure

#441849

Postby swill453 » September 13th, 2021, 12:05 pm

bungeejumper wrote:
swill453 wrote:Obviously I don't know how your Octavia does it, but my VW tyre pressure monitor doesn't physically monitor the air pressure. It measures the relative speed of all the wheels using the ABS sensors, and flags up discrepancies as tyre pressure loss.

That's intriguing. Sounds simpler than the usual valve sensors, but how does it cope with normal tyre wear, which will also cause divergent rotation speeds? Does it scream foul play if you fit a new (i.e. bigger) tyre, or maybe a slimline spare - which can quite legally have a smaller circumference than the other three?

Don't know the answers to those I'm afraid. I suspect it's less accurate than pressure sensors.

However it did correctly flag up a puncture to me before I could tell by looking at the tyre.

EDIT: seems like most of the answers are here http://www.vwpolo.net/tyre_pressure_los ... r-249.html

Scott.

brightncheerful
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Re: Tyre pressure

#441901

Postby brightncheerful » September 13th, 2021, 3:04 pm

from what i've read on-line:

The system on the Octavia does not have wheel mounted sensors, it uses the ABS system to monitor the wheel rotation speeds. If a tyre deflates, that wheel's rotation speed will increase out of proportion to the others, and also exceed the 'learned' values it has calculated within a short period of you resetting the system, after adjusting the pressures.

Passive TPMS does not measure your tyre pressure.
It only notices a quick change in a tyres rotation speed as measured from the speed/ABS sensor at each wheel.
If one tyre looses air quickly it will get smaller and will travel faster than the rest/ faster than before.
It will not notice any slow change.
You need to check your pressures regularly. The highway code suggests one a week.
Then before you move off reset the TPMS system.
It will also need resetting if you move the tyres/wheel around or have new tyre fitted.

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Re: Tyre pressure

#441969

Postby Breelander » September 13th, 2021, 7:08 pm

bungeejumper wrote:That's intriguing. Sounds simpler than the usual valve sensors, but how does it cope with normal tyre wear, which will also cause divergent rotation speeds? Does it scream foul play if you fit a new (i.e. bigger) tyre, or maybe a slimline spare - which can quite legally have a smaller circumference than the other three?


I have a VW Polo with this type of tyre pressure warning.

Yes, changing a tyre can cause a false positive warning. What you do in that case, after checking for yourself that the tyre pressures are correct of course, is press the hidden reset button. This tells the system to use the current ratio of rotation speeds as the new baseline, deviation from which will be flagged as a warning. My reset button is in the glove box.

swill453
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Re: Tyre pressure

#441971

Postby swill453 » September 13th, 2021, 7:11 pm

Breelander wrote:
bungeejumper wrote:That's intriguing. Sounds simpler than the usual valve sensors, but how does it cope with normal tyre wear, which will also cause divergent rotation speeds? Does it scream foul play if you fit a new (i.e. bigger) tyre, or maybe a slimline spare - which can quite legally have a smaller circumference than the other three?


I have a VW Polo with this type of tyre pressure warning.

Yes, changing a tyre can cause a false positive warning. What you do in that case, after checking for yourself that the tyre pressures are correct of course, is press the hidden reset button. This tells the system to use the current ratio of rotation as the new baseline, deviation from which will be flagged as a warning. My reset button is in the glove box.

Mine is similar, but you do it through the menus in the "infotainment" system.

(Slightly annoyed that "infotainment" isn't flagged as a spelling error...)

Scott.


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