Tyre pressure monitoring system accuracy

[sido]

Does anyone have information about the accuracy of the data stored in the trip?
I have noticed when I start up in the morning all wheels except rear passenger side ( 2.1bar) are same pressure (2.2bar) and temperature 10C on all four.
after short school drop trip. Front tyres 16C passenger side 2.1bar drivers side 2.2bar and rear tyres both 14 C and 2.2 Bar. I normally check pressure once a week and correct using a cigarette lighter powered air pump at 32 PSI. I have had my car for coming up to 2 months now and the air pump has not activated once, implying that all tyres are actually 32 PSI whereas the trip suggests otherwise.

 

[Aberdeenshire]

I might be reading this wrong but I don't see the problem. 2.2bar is 32psi, so all seems to add up pretty well?

 

[Alb]

The dashboard display isn't meant to be an accurate display of pressure, just a means of detecting a significant loss of pressure. It does read pretty close in my experience but I wouldn't use it as a reference.
Your pump will also not be that accurate so it's best to check tyres with an independent pressure gauge.
Note also that any comparison between reading devices must be done at the same temperature to be valid.

 

[Ozzie1989]

Your pump will also not be that accurate so it's best to check tyres with an independent pressure gauge.
Note also that any comparison between reading devices must be done at the same temperature to be valid.

Completely agree with this. We did a little experiment in work against a recently (same day) calibrated commercial air line gauge.

The little digital handheld gauges were the most accurate, but still out by 0.3 to 0.7psi. I know mine is consistently under reading by 0.5psi, which I'm cool with as it only cost me £3 from Amazon.

The worst offenders were the ones built into cheap pumps (e.g. Ring, Halfords etc.) where we found one to be over reading by 5psi. Quite dangerous actually.

Analogue gagues turned out to be a bit hit and miss as well, but then they are not meant for accuracy.

 

[sido]

Thanks for your replies all. I have to say I find it all a bit disconcerting. The trip may not accurate, the pump may not accurate and even digital hand held gauges may be out as well. My trip in itself indicates a difference of 0.1 bar randomly this is under 5%. Is there a simple way to make sure we are driving with 32 psi? Or should we just accept that we might be as much as 5% out and not worry about it?

 

[Hairyfool]

The only accurate gauge is one with a calibration certificate and you won't find one with a push on connector, it has to lock on to the threads AND depress the core pin.

Also as the only way to get an accurate tyre pressure is to slightly overfill and use the gauge to reduce the pressure to the target a separate gauge can't do it.

 

[TGMGee]

If tyre pressures are required to be precise, then we would all be checking pressures and temperatures, so one or two psi readings are not a cause for concern.

 

[Ozzie1989]

Honestly, it won't make a huge difference. If it's suddenly .5 bar down you know to check it.

Bear in mind that tyre pressures must be checked when cold. That doesn't mean only the coldest day in winter, just before driving and not at the height of a summer's day when the sun has been shining on the tyres.

In winter pressures will increase on a longer/faster drive due to friction heating up the air in the tyres. In summer, if standing in the sun for a long time, pressures can reduce once driving as the air cools the tyres down.

It is common to need to add air in winter time and remove some in summer to keep a consistent pressure.

Use the display as a guide and an aide memoire to check the tyres if things look a little more out than usual, but it's still no substitute for manually checking them with a gauge once a month (or more frequently if you do more than 500 miles per month).

E.g. as a fleet driver we must visually inspect tyres daily (check they don't look flat and tread is legal) and check tyre pressures at each fill up (approx 450-500) miles.

 

[Gomev]

Thanks for your replies all. I have to say I find it all a bit disconcerting. The trip may not accurate, the pump may not accurate and even digital hand held gauges may be out as well. My trip in itself indicates a difference of 0.1 bar randomly this is under 5%. Is there a simple way to make sure we are driving with 32 psi? Or should we just accept that we might be as much as 5% out and not worry about it?

How on earth did you/we manage before TPMS brought about all this concern ?

 

[Kithmo]

How on earth did you/we manage before TPMS brought about all this concern ?

A quick walk around and kick each one would suffice.

 

[sido]

Well I used to kick them, but now I have this trip record I thought it might be more accurate, clearly not! Will go back to kicking.

 

[Aberdeenshire]

Well I used to kick them, but now I have this trip record I thought it might be more accurate, clearly not! Will go back to kicking.

I say again: I don't see the problem and I wouldn't worry about. They are accurate enough for what they need to do in the real world unless your name is Lewis Hamilton. Unless you vary your tyre pressure for every trip depending on pay load, intended speed, ambient temperature, road moisture, etc, then you do not need more precision or decimal places in your TPMS.

 

[sido]

This morning I noticed a yellow triangle with an exclamation mark in it. It took me a minute or so to work out what the yellow U with a line in the middle was but then realised the tyre monitoring system was telling something.
moved over to steering wheel controls and called up the tyre pressure monitoring system clearly showing 0.9 bar drivers side front. Limped to my local tyre specialist and was back on the road in twenty minutes. £20 lighter in my wallet mind you. All wheels now showing 2.2 bar, it works!

 

[Alb]

They charged £20 to pump up your tyre?

 

[sido]

They charged £20 to pump up your tyre?

Yes Alb, but I thought that was reasonable, given they had to remove the tyre, remove a large screw, plug it and put the tyre back, test it and refit. Mind you, I have not had a puncture for about twenty years now so I could be out of touch but I prefer to think I am just lucky.

 

[Alb]

Lucky it was in the repairable area because if the tyre is scrap, you are committed to buying at least two replacements.

 

[Ozzie1989]

Lucky it was in the repairable area because if the tyre is scrap, you are committed to buying at least two replacements.

Why two?

 

[Alb]

You aren't likely to find another Ecopia so it's the only way you'll get a matching axle pair.

 

[Rocinante]

Why two?

It's advised that you change the tyre's on each axel at the same time (with the same tyre), so that they behave the same, ie have the same level of grip, tread pattern, wear etc,. If they are different they could react differently in extreme braking, and cause wear on components in regular use.

However, I'm sure it's open to much debate, how much effect this will actually have on day to day driving. It would be perfectly legal to change just one.

 

[sido]

Interestingly I have been following the post on the “Terrible default tyres“
and after this mornings events I shall shortly be replacing both fronts and maybe the backs as well.