Tyre pressures

Faults and Technical chat for the Jaguar F-Pace.
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frogmill0
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Joined: Tue Jan 16, 2018 11:36 am

Tyre pressures

Post by frogmill0 » Mon Dec 03, 2018 1:43 pm

I have the TPM set for 'Light Load' which means recommended tyre pressures of 34 psi all round.

At the weekend I checked the pressures and, using an electric compressor, inflated the tyres to 34 psi as shown by the digital gauge on the compressor. However, when I checked the figures with the Driver Information screen the latter showed all 4 tyres at only 30 psi. I didn't expect the two sets of figures to agree exactly but a discrepancy of over 10% seems too much. I can't tell which one is right because I don't have another pressure gauge. I can buy one, of course, but before I do that I thought I'd ask if anyone here has had the same problem and whether they ascertained if it was the TPM which was accurate or under-reading.

All help appreciated.
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Jim
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Location: Telford, Shropshire

Re: Tyre pressures

Post by Jim » Mon Dec 03, 2018 2:00 pm

frogmill0, I have wondered about this and whether there is a means of calibrating the car's readings. On my wife's little Peugeot it is possible to inflate the tyres to a the correct pressure using an independent gauge and then tell the car that that it is the correct pressure. Which it then accepts and updates the indicated values and then calculate variations from these calibrated values. A fairly simple but effective method.

When I lived in Germany (a couple of decades ago) the petrol stations had to have their tyre pressure gauges calibrated every 2 years (if I recall) and I always felt reasonably confident when selecting the little charging pod with the most recent calibration date that the indicated pressure I was inflating my tyres to was probably very close to what it should be - not so sure where you would get an accurate gauge from in the UK!
Oct 2016 - 2.0 D, Portfolio, Auto, AWD, Ultimate Black, Light Oyster, 14-Way Front Seats with Passenger and Drivers memory pack, electrically adjustable steering wheel, 360⁰ parking aid, ICTP 380W, LED headlights, remote rear seat release.


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catwoman
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Re: Tyre pressures

Post by catwoman » Mon Dec 03, 2018 2:22 pm

I've noticed the TPMS does seem to need a little time to adjust when you have altered the tyre pressures. Last week I got an offside rear low pressure warning (at 30psi) on the dash so I checked my pressures at a local garage and re-inflated my tyres which were all a little on the low side, possibly due to cold weather. I was using one of those digital air-lines and I inflated all my tyres to 34psi. I drove home (just a couple of slow miles), during which time the onboard display was reading both tyres on the nearside at 32psi and on the offside at 34psi. The following day when I checked the onboard display (without having altered my tyre pressures again) it was reading 34psi all round. This made me wonder if the computer does not always give an accurate immediate reading, but is maybe working on some kind of average over distance/time . . a bit like the mpg and miles-to-service indicators also adjust themselves according to time elapsed and driving style factors.
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Jagfpacejk
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Re: Tyre pressures

Post by Jagfpacejk » Mon Dec 03, 2018 6:15 pm

Also remember the temperature of the rims will affect your reading on the TPMS.

In winter months when the rims are cold the reading on the display will be lower then the actual pressure, once you have warmed the rims up by driving then the temperature will rise.

In the winter months i used to add a couple of Psi to stop the PMS warning on the dash.
Ex Owner of a Pre Launch 1st Edition Supercharged V6 and a Ex Owner of 1st Edition Diesel V6


frogmill0
Posts: 44
Joined: Tue Jan 16, 2018 11:36 am

Re: Tyre pressures

Post by frogmill0 » Tue Dec 04, 2018 1:16 pm

Thanks for your comments and advice.

I mentioned the problem to my neighbour who lent me his digital pressure gauge and that gave me a third set of readings. They were closer to those shown on the TPMS so I've concluded that my compressor is reading high and the TPMS is probably reasonably accurate.
3.0d 'S' in Rhodium Silver. ICTPro, 825w Meridian, Cold Climate pack, 14 way memory seats, pan roof.


Smitten
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Joined: Mon Dec 11, 2017 9:53 am
Location: SW London

Re: Tyre pressures

Post by Smitten » Tue Dec 04, 2018 6:40 pm

Just a thought - when you compress air it gets warmer. Decompress and it gets much cooler. Perhaps your freshly pumped tyres are a little warm?
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frogmill0
Posts: 44
Joined: Tue Jan 16, 2018 11:36 am

Re: Tyre pressures

Post by frogmill0 » Wed Dec 05, 2018 11:34 am

Thanks, I hadn't thought of that and it would perhaps explain why the gauge on the compressor gave a higher reading immediately after inflation. On the next check I'll do a comparison of the readings before I start the compressor.
3.0d 'S' in Rhodium Silver. ICTPro, 825w Meridian, Cold Climate pack, 14 way memory seats, pan roof.


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