Quick TPMS question

[such01]

Checked my TP's when i bought the car 2wks ago, and the Tp's were ok, around 37 psi all round.
Checked them again today and they had fallen to around 30, so topped to 39, which is is the recommended pressures for my wheel size.

I reset the TPMS, but not sure if it correct as it stated "reset runflat indicator" or something similar.

Does this indicate that the car should be on runflats? It may have been and was changed, does the TPMS still work in this case?

I did not get any warning with the loss of pressure since it was last checked

Thanks

 

[Harry82]

the TPMS will work regardless whether on runflat tyres or not, that much i can tell you for sure.

'reset runflat indicator' is just the terminology chosen, it's not suggesting that you should have runflat tyres.

it does seem strange that the psi dropped by 7psi without a message...did all tyres drop by the same amount or just one? were the pressures checked using the same machine or different ones? it could be that the machine you used initially was giving an inaccurate reading.

 

[whitenemesis]

Pressure drop due to the much cooler ambient temps lately?

 

[LTD]

Pressure drop due to the much cooler ambient temps lately?

Good shout.

It's getting wintery cold up here in Glasgow and my tyre pressures have dropped by about 4psi all round in the last week or so.

 

[markjay]

If you have the basic ESP-based TMPS, then my experience is that it won't alert you for minor pressure drops, but only when one tyre has deflated significantly compared to the others.

The sensor-in-valve TPMS system might be more accurate/sensitive.

 

[such01]

the TPMS will work regardless whether on runflat tyres or not, that much i can tell you for sure.

'reset runflat indicator' is just the terminology chosen, it's not suggesting that you should have runflat tyres.

it does seem strange that the psi dropped by 7psi without a message...did all tyres drop by the same amount or just one? were the pressures checked using the same machine or different ones? it could be that the machine you used initially was giving an inaccurate reading.

Yes all tyres had dropped, which I was suprised to see. Used the same manual tyre gauge to measure too. I would have expected a light to come on too.
Maybe it may be due to the colder weather, although the lowest temp has been around 10 deg C

Thanks

 

[PobodY]

If you have the basic ESP-based TMPS, then my experience is that it won't alert you for minor pressure drops, but only when one tyre has deflated significantly compared to the others.

In a nutshell; it only gives you a warning if the pressure in one tyres drops below the others. - If they all drop, then there's no difference between the wheels so it doesn't register.

(Have I got that right?)

 

[whitenemesis]

Yes

 

[markjay]

In a nutshell; it only gives you a warning if the pressure in one tyres drops below the others. - If they all drop, then there's no difference between the wheels so it doesn't register.

(Have I got that right?)

This is correct, but in addition, on the occasion that I did have a puncture, I noticed it well before the TPMS alert came-up (it was a front tyre and the car was pulling to one side), so my conclusion is that it requires a significant loss of pressure (i.e. significant relative change in rotational speed) before it raises the alarm.

 

[whitenemesis]

IIRC it's about 25-30% difference before it triggers

 

[markjay]

IIRC it's about 25-30% difference before it triggers

This makes sense....

 

[such01]

Thanks all, so by the time the TPMS comes on then you really are in trouble!!

 

[markjay]

Thanks all, so by the time the TPMS comes on then you really are in trouble!!

Yes, but only assuming the pressures were correct and the system correctly reset prior to that.

I had it come up once after a garage inflated the four tyres to varying pressures for some reason, and TPMS didn't like it.

 

[PobodY]

I've had the opposite. - Tyre pressure warning whilst on the M6, but when I checked the pressures (once cold) they were all about the same.

I appreciate that hot tyres have more pressure (that's Boyle's Law), but not 25% more in one tyre alone.

 

[whitenemesis]

Here's a reasonable explanation of the two types of tpms.

Tyre Pressure Monitoring System | ATS Euromaster

 

[markjay]

I've had the opposite. - Tyre pressure warning whilst on the M6, but when I checked the pressures (once cold) they were all about the same.

I appreciate that hot tyres have more pressure (that's Boyle's Law), but not 25% more in one tyre alone.

We are mostly referring here to our experience with a single car, and we are logically deducing that our experience is applicable to all cars (or at least to all cars of same model). But we should also keep an open mind to the possibility that our own car may be behaving differently to how it should... in short it may have been the result of a malfunction of some sort?

 

[whitenemesis]

Must admit I had a couple of false alarms in my 203. I had tpms coded in as a retrofit and a couple of times had the dash go red and boing at me. Pulled over immediately and checked tyres, all fine.

The ABS/ ESP system is quite crude compared with the valve mounted sensor s

 

[markmifsud]

As above, I coded in the ABS style tpms and it was warning me at all sorts of odd times for nothing.