TPMS accuracy

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calnorth
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Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by calnorth »

Whats not said by tyre manufacturers: (variations of temperature , volume and pressure)

Physical gas law (Boyles) expresses clearly that with a rise in temperature and a tyre that cannot expand much the internal pressure increases. The cold pressure setting is lower than the road running pressure so that when the tyre warms it reaches an expected higher pressure. This higher pressure is the working pressure for the tyre rolling under load. Its a small pressure range (say 33 to 37psi) at which the tyre can operate efficiently....and is according to the manufacturers tests.

There's probably a detailed technical blurb on it somewhere, where the small working pressure range is explained. Obviously if the tyre pressure is say 40 psi or 25 psi, in both instances the tyre shape will change so unacceptable wear pattern/performance results (tread edges or centre).

Anyway, simply set the recommended pressures when the tyres are cool/cold with a reliable pressure gauge. TPMS in my short QQ experience picked me up on low pressure last week. Forced me to buy pressure gauge.
Mk2 Qashqai Facelift - J11b (2017–and onward)
1.6 Dig-T N-Connecta

Icarus
Posts: 23
Joined: Sat Nov 16, 2019 10:02 pm
Qashqai Model: Mk.2 Qashqai - J11 (2013–2017)

Post by Icarus »

Good thread. Calnorth, you've almost (I think) answered a question that I've been trying to fathom out for a week or so now. Is the psi figure on the car the optimum operating temperature...or is it acceptable to allow for a variance....and if so, how much?

I've tried varying footpumps and all give off terrible readings. Some (from Halfords) go from something like 28 to 40 in one pump...obviously it's rubbish. Now that I have a the QQ compressor, it's not really accurate to the readings we need. So I thought I'd go with Sainsbury's digital one, and It's just making things more confusing. I set it to 33/30 and got back in...only to find the tyres got up to 32/29! It was a cold day and I'd only driven 4 miles. I went to a friends house nearby and waited a couple of hours.....wen't back to Sainsbury and set it to 34/31. Now the gauge shows 37/33!

The situation has been made more confusing now as it's unnaturally hot (we're in Scotland and getting 22c-24c...yes, you read that correctly) and with the car being in direct sun, the tyres are starting off hotter than normal (34-31 getting up to 37/33). I'll be happy enough leaving it if 37/33 or thereabouts is 'normal'....but obviously when it gets colder again, I'll need to adjust the pressure accordinly!
2016 - N-Connecta 1.5 DCI. Black. Diamond cut alloys. Panoramic roof.
User avatar
calnorth
Posts: 2719
Joined: Mon Feb 11, 2019 2:01 pm
Qashqai Model: Mk.2 Qashqai Facelift - J11b (2017–2021)

Post by calnorth »

Hope I'm not repeating anybody here. The sensors should adhere to the law:
.......................................
Characteristics of the TPMS according to EU law:

1. Warning in the event of pressure loss in an individual tyre (within 10 minutes):
20% lower than operating pressure (Pwarm) at 1.5 bar

2. Warning in the event of pressure loss in all four tyres (sudden and creeping loss):
20% lower than operating pressure (Pwarm) at 1.5 bar

Determination of pressure loss at speeds of 40 km/h to the maximum driving performance of the vehicle

Data transfer on 434 MHz
..................................................

1.5 Bar is about 22 psi (variable operating centre point - Pwarm)
Tyre pressure can change by about 1psi per 5deg C

Tyre out of required working pressure range:
So at about +/- 7 psi off recommended tyre pressure the TPMS should present an alarm to the driver. And thats after the tyre has reached its operating temperature in use at 40kph.

I'd expect TPMS to alarm almost immediately if pressures were much lower/higher than above +/- psi parameter...before the car was started.

The recommendation appears to be:
Pump tyres to recommended spec when tyres cold.
Check pressures monthly...adjust when cold (I started recording figures...Nissan TPMS doesn't incorporate a memory AFAIK)
Forget TPMS until a warning appears. You can monitor it on the fly and I stopped doing that....daft.

I got a low pressure warning about 4 weeks back ...after a mild-ish winter.
I fiddled about trying to get running pressures to spec when warm which is daft really. They'll fluctuate either side of the spec in use and at rest (warm/cold). TPMS checks they don't go too far out and providing TPMS is calibrated/working right.

At a guess I'd say tyre pressures will vary +/- 10% in use anyway. I've never been bothered till now..... :oops:
Mk2 Qashqai Facelift - J11b (2017–and onward)
1.6 Dig-T N-Connecta
Icarus
Posts: 23
Joined: Sat Nov 16, 2019 10:02 pm
Qashqai Model: Mk.2 Qashqai - J11 (2013–2017)

Post by Icarus »

calnorth wrote: Wed Jun 03, 2020 7:36 am Hope I'm not repeating anybody here. The sensors should adhere to the law:
.......................................
Characteristics of the TPMS according to EU law:

1. Warning in the event of pressure loss in an individual tyre (within 10 minutes):
20% lower than operating pressure (Pwarm) at 1.5 bar

2. Warning in the event of pressure loss in all four tyres (sudden and creeping loss):
20% lower than operating pressure (Pwarm) at 1.5 bar

Determination of pressure loss at speeds of 40 km/h to the maximum driving performance of the vehicle

Data transfer on 434 MHz
..................................................

1.5 Bar is about 22 psi (variable operating centre point - Pwarm)
Tyre pressure can change by about 1psi per 5deg C

Tyre out of required working pressure range:
So at about +/- 7 psi off recommended tyre pressure the TPMS should present an alarm to the driver. And thats after the tyre has reached its operating temperature in use at 40kph.

I'd expect TPMS to alarm almost immediately if pressures were much lower/higher than above +/- psi parameter...before the car was started.

The recommendation appears to be:
Pump tyres to recommended spec when tyres cold.
Check pressures monthly...adjust when cold (I started recording figures...Nissan TPMS doesn't incorporate a memory AFAIK)
Forget TPMS until a warning appears. You can monitor it on the fly and I stopped doing that....daft.

I got a low pressure warning about 4 weeks back ...after a mild-ish winter.
I fiddled about trying to get running pressures to spec when warm which is daft really. They'll fluctuate either side of the spec in use and at rest (warm/cold). TPMS checks they don't go too far out and providing TPMS is calibrated/working right.

At a guess I'd say tyre pressures will vary +/- 10% in use anyway. I've never been bothered till now..... :oops:
Thanks for that! I only found the various screens on the wheel at the beginning of the year and they were 1psi +/- at any given time so I was fine with it......until I decided to try & get it bang on....now it's gone breasts North trying to get it right :D

I'll try again to get it closer but knowing they're within an acceptable range will give me peace of mind! Cheers!
2016 - N-Connecta 1.5 DCI. Black. Diamond cut alloys. Panoramic roof.
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