Tyre (Tire) pressure question

[Ross]

My tyre pressure plate says 2.6 front 2.7 rear at 20C (68F)
We all know to check tyre pressures when 'cold' but at
the moment I get in my car in the morning and the temperature is 10C, not 20C.
My tyre pressures read 2.4 and 2.5 then go to 2.5 and 2.6 within a mile,
then to the correct 2.6 and 2.7 within a few miles.
Enthusiastic driving with a slight increase in outside temperature they go to 2.7 and 2.8
So....
What is the correct pressure to set my tyres at 10C?

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[bn8959]

I just adjusted so the pressure deviation read zero in PCM. It should compensate for temperature etc. note I deselected the ‘full load’ setting too, which is the default from factory. When I turned that off I got a +7psi deviation showing, so just let air out until they read zero.

 

[whitex]

I also just adjust based on the PCM (or instrument cluster, or phone app) display. It required re-adjustment after few months, but even though the actual tire pressures vary, as long as my deviation is 1 psi or less, I'm good with it. There is a setting in the PCM which sets the expected tire pressures based on type of tire and full or half load, so set that first, then adjust. The expected setting differ between factory stock all-season and winter tires (the two tires/wheels I use), but surprisingly, PCM expects slightly different values than my door jam plate/sticker. At first I thought the door jam sticker would match the PCM for the tires which came from the factory, but it does not, so I assume the PCM has newer information.

 

[WuffvonTrips]

My tyre pressure plate says 2.6 front 2.7 rear at 20C (68F)
We all know to check tyre pressures when 'cold' but at
the moment I get in my car in the morning and the temperature is 10C, not 20C.
My tyre pressures read 2.4 and 2.5 then go to 2.5 and 2.6 within a mile,
then to the correct 2.6 and 2.7 within a few miles.
Enthusiastic driving with a slight increase in outside temperature they go to 2.7 and 2.8
So....
What is the correct pressure to set my tyres at 10C?

That's the question I recently sought answering for myself- after much Googling turning up every opinion under the sun, a Firestone website offered the clear advice of inflating to and maintaining at the specified pressures regardless of the reference temperature and the current ambient temperature. I assume that is sensible, as the mass of the vehicle being supported by the tyres doesn't change with temperature. I used a digital gauge and checked against the TPMS readings once on the move, IIRC they all tallied.
EDIT- afterthought- I guess this implies that, for high-energy conditions e.g. on a track, tyres would need air letting out to avoid overinflation at high internal temps. Hopefully our more expert members can confirm or refute as appropriate.

 

[whitex]

That's the question I recently sought answering for myself- after much Googling turning up every opinion under the sun, a Firestone website offered the clear advice of inflating to the specified pressures regardless of the reference temperature and the current ambient temperature. I assume that is sensible, as the mass of the vehicle being supported by the tyres doesn't change with temperature. I used a digital gauge and checked against the TPMS readings once one the move, IIRC they all tallied.

The issue is that the pressures change with temperatures. If I park my Taycan on the driveway, one side is getting heated up by the sun and the other is not. If I pump them all up to the same pressure, then repark the car backwards, the pressures will be different on left vs. right. Furthermore, if I pump the tires on a hot day, then winter comes, the pressures can get low enough to trigger a pressure warning. This is why the Taycan has a compensated temperature monitoring, and it literally tells you how much to inflate or deflate each tire at whatever temperature the car is in (though from experience, it helps if it's in a garage, so all 4 tires are at the same temperature).

 

[WuffvonTrips]

The issue is that the pressures change with temperatures. If I park my Taycan on the driveway, one side is getting heated up by the sun and the other is not. If I pump them all up to the same pressure, then repark the car backwards, the pressures will be different on left vs. right. Furthermore, if I pump the tires on a hot day, then winter comes, the pressures can get low enough to trigger a pressure warning. This is why the Taycan has a compensated temperature monitoring, and it literally tells you how much to inflate or deflate each tire at whatever temperature the car is in (though from experience, it helps if it's in a garage, so all 4 tires are at the same temperature).

It'd be even better if TPMS could measure pressure before the car has been driven a minimum distance.

 

[whitex]

It'd be even better if TPMS could measure pressure before the car has been driven a minimum distance.

Engineering limitation/compromise. TPMS sensors/transmitters are battery powered, so in order to extend battery life, they only turn on when they detect acceleration/g numbers consistent with >~15mph. Most people drive less than 2hrs of 24hrs each day. If the transmitters stayed on 24/7, their life would be reduced 12x, so instead of changing your TMPS every 7 years, you'd be changing them every 7 months or sooner.

 

[Porsche-Guru]

My tyre pressure plate says 2.6 front 2.7 rear at 20C (68F)
We all know to check tyre pressures when 'cold' but at
the moment I get in my car in the morning and the temperature is 10C, not 20C.
My tyre pressures read 2.4 and 2.5 then go to 2.5 and 2.6 within a mile,
then to the correct 2.6 and 2.7 within a few miles.
Enthusiastic driving with a slight increase in outside temperature they go to 2.7 and 2.8
So....
What is the correct pressure to set my tyres at 10C?

Like others have said... just use the deviation measurement to get your tyre pressures to the correct value... that is the simplest way.

This is what has worked for me....
- Reset TPMS (just choose different tyre set and then set back to actual tyres)
- Drive for a few miles, so that all tyres can come up in temperature; rather than be be stone cold as in UK mornings !
- My work place is about 20 miles, and all tyres are at a similar temperature.
- Check deviation and actual pressures
- Fill/ release air according to deviation
- Reset TPMS
- My tyres now usually show absolutely correct values and zero deviation.

The only reason I drive a few miles before filling up is to get all 4 tyres to similar temperatures, so the deviation is minimal.

As somebody else has stated, tyres can easily have a 15ºC variation, if one side is exposed to the sun on a hot day. I just try and minimise the temp variation by driving for a few miles to normalise the tyre temperature.

 

[Tooney]

At first I thought the door jam sticker would match the PCM for the tires which came from the factory, but it does not, so I assume the PCM has newer information.

Tire pressure info is in PCM...instructions....technical data. Also been revised a couple times in TSBs.
I have no idea whether the PCM technical data matches the TPMS settings system or not.

 

[Vercingetorix]

It'd be even better if TPMS could measure pressure before the car has been driven a minimum distance.

I have a handheld Autel TS508 and can read tyre pressures before driving. Bought a kit with 8 TPMS sensors and the tool was basically free.

 

[rim23]

My tyre pressure plate says 2.6 front 2.7 rear at 20C (68F)
We all know to check tyre pressures when 'cold' but at
the moment I get in my car in the morning and the temperature is 10C, not 20C.
My tyre pressures read 2.4 and 2.5 then go to 2.5 and 2.6 within a mile,
then to the correct 2.6 and 2.7 within a few miles.
Enthusiastic driving with a slight increase in outside temperature they go to 2.7 and 2.8
So....
What is the correct pressure to set my tyres at 10C?

I believe it doesn’t matter if you adjust the tire pressure on cold tires to the recommended values whether cold is 10 or 20 or even 30. It must be on cold tires. Period. Each 10 degrees add/remove 0.1 bar.

So if the cold temperature at a specific period of the year is 20, then you should set your tire pressure to the one recommended one by PCM on one of your “cold” runs.

If it gets colder, remember to adjust. Eg, it’s again the same pressure, but cold temperature will be 10. Then, while you drive, the temperature in tires increases and the pressure raises as well (hello physics).

tl;dr:
Always set to recommended tire pressure on cold tires and remember to adjust whenever daily temperature drops/increases.

PS I always correct the tire pressure on every 10 degrees changes. Eg - the daily temperate is 10, I adjust the pressure. It becomes 0, I adjust again. It’s -10, I adjust again.

 

[whitex]

Tire pressure info is in PCM...instructions....technical data. Also been revised a couple times in TSBs.
I have no idea whether the PCM technical data matches the TPMS settings system or not.

PCM is updated more often than the door jam plate/sticker (which is probably never updated after the car leaves the factory). PCM values are also the ones used to display TPMS warnings on the instrument cluster.

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