Tyre Pressures

Marc

Marc

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I've had my car (from new) for 7 months and it's the first car I've had with tyre pressure monitors. A few weeks ago, I started to get tyre pressure warnings as they had dropped to 27/28 (recommended is 32). I know they drop a little in cold weather but is this normal? It's something I've ever worried about on previous cars and have only bothered putting air in when they looked low.

I get the feeling my fuel consumption may have been unnecessarily high over the years. :help:
 
Pressure will drop a little when cold which is why your advised to check/inflate tyres when cold. How often do you check tyre pressures? I think most garages forecourt air pumps will probably differ in their pressure readings slightly so you'll never get a true reading unless you splash out on a fancy gadget to do so. Waiting until the tyres look "Low" is the wrong way to go about it, unnecessary wear on your tyres and maybe a slight increase in fuel consumption. Get into the habit of checking tyres on at least a weekly basis, it will probably make the tread wear on your tyres last longer.
 
Manually check the pressures when the tyres are cold. Inflate to required temp, then reset the TPMS and the warnings will stop, unless you have a slow puncture.
My TPMS doesn't warn about changes in pressure due to temp changes.
 
Mine can drop by about 0.2 bar when it's cold which I think is about 3psi. They soon warm up with driving to the usual readings. I over inflate at a garage then use a RaxeX gauge to drop them all down to the pressures I want the next morning.
 
frank said:
you'll never get a true reading unless you splash out on a fancy gadget to do so.
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As I said, the car monitors the pressures and I also have an iphone/app that links to it.

Bobsyeruncle said:
Manually check the pressures when the tyres are cold. Inflate to required temp, then reset the TPMS and the warnings will stop, unless you have a slow puncture.
My TPMS doesn't warn about changes in pressure due to temp changes.
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It's difficult for me to check the pressures manually for physical reasons so I have to rely on the readings from the car/iphone app.

gman said:
a RaxeX gauge
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What's one of them?
 
fabs said:
It's difficult for me to check the pressures manually for physical reasons so I have to rely on the readings from the car/iphone app.
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If the warning keeps going off, you'll need to inflate them to correct pressure. Somewhere like kwikfit will check them for you.
 
fabs said:
As I said, the car monitors the pressures and I also have an iphone/app that links to it.

It's difficult for me to check the pressures manually for physical reasons so I have to rely on the readings from the car/iphone app.
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Does the iPhone app and car monitors put air in when needed? ...no. I'm sure a friend could oblige you be helping in that department.
 
frank said:
Does the iPhone app and car monitors put air in when needed? ...no. I'm sure a friend could oblige you be helping in that department.
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I think we may be at cross purposes. I mentioned the app with regards to monitoring the tyre pressures. My wife put air in them for me on this occasions.
 
Get S** to do a manual check every week or 2 or at least as soon as you get a warning from the gizmos!
 
No, it's not normal for winter to cause the warming system to go off, though a small drop - possibly 5psi - is likely normal in very cold weather.

We have 2 cars with a pressure warming system: 1 of them has never triggered in the 18 months we've had it, while the other triggers every 3-4 months & requires the tyres re-pressurising/system re-setting. It seems that some rims are better at sealing than others. My wife's previous beetle had a terrible time keeping air in the tyres, and the guys that ran the tyre fitters we used commented that VW rims of that design were known to seal poorly.
 
Oxygen molecules pass through the tyre's rubber. Some places offer to fill them with Nitrogen, which has larger molecules and therefore doesn't go through the tyre. Tyres dropping 5psi over a long period of time isn't surprising. By the time your tyre begins to look flat it has lost considerable pressure.
 
an1uk said:
Oxygen molecules pass through the tyre's rubber. Some places offer to fill them with Nitrogen, which has larger molecules and therefore doesn't go through the tyre. Tyres dropping 5psi over a long period of time isn't surprising. By the time your tyre begins to look flat it has lost considerable pressure.
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does it i allways thought the chemical weight of nitrogen was 14 and oxygen 16?
which makes nitrogen a little easier to escape.
 
according to the AA the main reason for using N is

For passenger car tyres the main claims seem to be: Less corrosion – because unlike air there's no moisture in pure nitrogen.
 
I'm sure I read a discussion about how there's very little nitrogen in these places to be of any real use because pure nitrogen would cost a fortune? Just a vague memory though so not sure.

My local tyre specialist used some tyre sealant on my wife's car because it was losing air through the rim and it seems to have worked great. He buffed the alloy rim on the inside down first.
 
Yes, normal for them to loose some in cold weather, but also is normal for them to loose some over a gradual period of time - so potentially over past 7 months, they have been loosing slightly and then the cold period has just tipped it into the warning range for your sensors :)
 
I have had my car from new for just over 2 years and I have never had a tyre pressure monitor warning, I check the pressures now and again but I have never had to put air into the tyres.
 
andyred said:
Yes, normal for them to loose some in cold weather, but also is normal for them to loose some over a gradual period of time - so potentially over past 7 months, they have been loosing slightly and then the cold period has just tipped it into the warning range for your sensors :)
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Cheers Andy, that makes sense.
 
Suvv said:
I have had my car from new for just over 2 years and I have never had a tyre pressure monitor warning, I check the pressures now and again but I have never had to put air into the tyres.
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Ok, that's interesting and very different to what Andy said. Definitely something to keep an eye on over the coming months.
 
gman said:
I'm sure I read a discussion about how there's very little nitrogen in these places to be of any real use because pure nitrogen would cost a fortune? Just a vague memory though so not sure.

My local tyre specialist used some tyre sealant on my wife's car because it was losing air through the rim and it seems to have worked great. He buffed the alloy rim on the inside down first.
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The atmosphere is about 78% nitrogen, and nitrogen zero (i.e. pure nitrogen) isn't expensive. The discussion might have been about Helium.

Sealant and a clean, scratch & corrosion-free rim all help with sealing.

fabs said:
Ok, that's interesting and very different to what Andy said. Definitely something to keep an eye on over the coming months.
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They will lose *a little* over time, but not necessarily very much. As I understand it, the sensor that determines tyre pressure problems looks for differences in rotational speed, a soft tyre dragging slightly and rotating slightly slower - it looks for differences between tyres, so if all tyres drop their pressure evenly due to temperature then the system won't detect anything.
 
The problem nitrogen is trying to remove is that most compressed air is not dry.

High end motorsport (F1 / high end GT) uses nitrogen.

Mid level motorsport uses compressed air that has been through a dryer to remove any moisture from the air.

Club level motorsport normally uses ordinary compressed air as drying equipment is expensive, or taking compressed air in bottles adds expense and logistic issues.

Ordinary compressed air contains moisture and that causes pressures to change as tyres get warm through usage on road or track.

When using nitrogen or dry air, the tyres have to be completely purged of 'normal' air before they can be filled, a process that takes several total deflations and reinflations to complete.
 
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fabs said:
I've had my car (from new) for 7 months and it's the first car I've had with tyre pressure monitors. A few weeks ago, I started to get tyre pressure warnings as they had dropped to 27/28 (recommended is 32). I know they drop a little in cold weather but is this normal? It's something I've ever worried about on previous cars and have only bothered putting air in when they looked low.

I get the feeling my fuel consumption may have been unnecessarily high over the years. :help:
Click to expand...

Simple question!! Far too many over technical answers trying to out do each other with their knowledge of science!!

In simple terms: Yes tyre pressures will drop over time. They do also drop more in colder climates.
If they continue to drop often then it can be a number of things don't over look cracked Alloys (Quite common on larger Alloys from pot holes etc).
Get some soapy water sprayed around the tyres & beads and look for bubbles!! Also spray around the valves. Good Luck Mate.
 
ancient_mariner said:
it looks for differences between tyres, so if all tyres drop their pressure evenly due to temperature then the system won't detect anything.
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Hmm, I think things are still a little confused. This is what my tyre pressure monitor looks like on the app, this is the same data as displayed in the car and these matched the readings on the machine at the petrol station.

IMG_0102.PNG

When the warning first went off, they were all around 28/29 PSI so I don't think it's a case of there having to be differences between the tyres in order for it to display a warning.

Oxford_Matt said:
In simple terms: Yes tyre pressures will drop over time. They do also drop more in colder climates.
If they continue to drop often then it can be a number of things don't over look cracked Alloys (Quite common on larger Alloys from pot holes etc).
Get some soapy water sprayed around the tyres & beads and look for bubbles!! Also spray around the valves. Good Luck Mate.
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Thanks Matt. I'll keep an eye to see if they go down by a substantial amount again but will try that when I get the chance.
 
Curious - then I clearly know nothing about how your car works.
 
I didn't even know cars had tyre pressure monitors!

I check mine once a week when I fill up with fuel, being an older BMW, the alloys are a bit corroded and leak air.

One of them leaks more than normal so is often 20-25 come the weekend and it should be 38 ish.
 
noneforit said:
I didn't even know cars had tyre pressure monitors!

I check mine once a week when I fill up with fuel, being an older BMW, the alloys are a bit corroded and leak air.

One of them leaks more than normal so is often 20-25 come the weekend and it should be 38 ish.
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Yes my previous BMW had them as standard due to run flat tyres, wife's Mercedes has them - useful, but I still do regular checks myself.

I think they're more to worn of a low pressure - both lots I've had would either alert if one of the 4 was lower than the others or if they dropped below a (presumably) set amount. Very good if you've a slow or just picked up a puncture.
 
Some have proper sensors that check the valve and actual tyre pressure and others use the abs wheel sensors and notice when the circumference changes too much.
 
I have a notice on my desk telling customers of how lower weather temps will cause lower tyre pressures and may trigger warning lights on the dash, what to do in the case of a warning light, we now advise customers that claim the sensors are faulty, and claim to have checked the tyre pressures and found them to be correct, that if we check and only the pressures are at fault, IE the sensors are working correctly, that there will be a charge, people don't want to pay 20p or whatever on a forecourt to use the air machine but think it's ok to expect a technician to stop whatever job they are doing to check/inflate their tyres, only a very small percentage of fault claims actually turn out to be faulty sensors.
Exceptions are done of course, elderly disabled customers will get a but of leeway if they're prepared to wait till a technician is free.
IIRC most handbooks have advise on simple home maintenance, levels, pressures etc and a time schedule, but, hey, who reads a manual, just phone the dealer and moan.
 
mj4456 said:
I have a notice on my desk telling customers of how lower weather temps will cause lower tyre pressures and may trigger warning lights on the dash, what to do in the case of a warning light, we now advise customers that claim the sensors are faulty, and claim to have checked the tyre pressures and found them to be correct, that if we check and only the pressures are at fault, IE the sensors are working correctly, that there will be a charge, people don't want to pay 20p or whatever on a forecourt to use the air machine but think it's ok to expect a technician to stop whatever job they are doing to check/inflate their tyres, only a very small percentage of fault claims actually turn out to be faulty sensors.
Exceptions are done of course, elderly disabled customers will get a but of leeway if they're prepared to wait till a technician is free.
IIRC most handbooks have advise on simple home maintenance, levels, pressures etc and a time schedule, but, hey, who reads a manual, just phone the dealer and moan.
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People just don't seem to bother with their cars anymore.

When I met my other half a few years back, she never checked any of the fluids in her car or the tyre pressures.

Most people just take them to a garage for it's extortionately priced service and like in ignorance in the hope nothing will go wrong.

In the last 12 months I have changed the discs and pads all round, the spark plugs, air filter, drained and replaced the coolant and this weekend I will be changing the oil and gearbox oil.

Probably cost me a third of what I would have paid at a garage, what I saved pays towards a photographer for our wedding :)
 
noneforit said:
People just don't seem to bother with their cars anymore.
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Cars are designed to not need user-input, and almost to prevent it now, so hardly surprising that most users never check fluids or pressures until told to do so.
 
ancient_mariner said:
Cars are designed to not need user-input, and almost to prevent it now, so hardly surprising that most users never check fluids or pressures until told to do so.
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I would say it depends on the age of the car.

If it's < 5 years old then you could argue that.

My other halfs is a 2011 French tin can and there is certainly no tyre pressure warnings. In fact there wasn't even a brake pad warning sensor on the front pads when I changed then last year!

My 2002 BMW has brake pad warning sensors and it's 9 years older than hers.

You should still do a few checks, even on a modern car.

Relying on sensors are fine for the most part but a few quick checks every few months makes me feel a bit better at the very least. I can then spot if my oil has dropped towards the low mark before I have get a warning light, that way I can get it sorted quickly.

I guess I am the only one who has top up oil, anti freeze/ coolant and a battery charger in the garage just in case? Always be prepared..
 
ancient_mariner said:
Cars are designed to not need user-input, and almost to prevent it now, so hardly surprising that most users never check fluids or pressures until told to do so.
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Do they? All the same top up and check points are still there.
 
nilagin said:
Do they? All the same top up and check points are still there.
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yes but what he is saying is a lot of cars tell users when things are low so people percieve they dont need to check all the time.
 
Mr Bump said:
yes but what he is saying is a lot of cars tell users when things are low so people percieve they dont need to check all the time.
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Yeah I think a common error is to mistake the oil pressure warning light as just an indicator the oil needs topping up when they feel like it.
 
an1uk said:
Yeah I think a common error is to mistake the oil pressure warning light as just an indicator the oil needs topping up when they feel like it.
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Thats right my 7 year old citroen C3 says oil is OK on the dash even when it gets half way down the dip stick which can't be good.
I had a slight issue with it a few years ago when i had a gasget leak and it was weepeing oil down the side of the block.
I ended up putting about half a pint in every 500 miles as i kept checking it but the oil status just kept saying OK.
 
noneforit said:
I guess I am the only one who has top up oil, anti freeze/ coolant and a battery charger in the garage just in case?
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Well that makes 2 of us at least :D

Mr Bump said:
Thats right my 7 year old citroen C3 says oil is OK on the dash even when it gets half way down the dip stick which can't be good.
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Us of an older generation would always make sure our cars oil level was hovering just under the max mark.
It seems these days its better to have the oil level somewhere between Min & max.
 
I'm the same and make sure oil is half way to allow for anything like the ground not being perfectly level etc. Cabin filters is probably the most common thing never touched by garages which annoys me because that's the big part of the air you are breathing in whilst driving.
 
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