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Hi guys
Someone please help.
I’ve always but under the impression you set your tyre pressures when the wheel is cold.
But after having the display on the dash telling us each wheel temperature and pressure. Obviously once the tyre becomes hot the pressure starts going through the roof.
Is it best to set the pressure once the tyre is up to a nominal 20 degree or so.
Running 19inch wheels on my m240 and currently just change the tyres to the Kumho non run flats from the Pirelli o zero which came with the wheels at purchase. Btw it’s a much softer ride but feels a little more yawning at high speed, which is why I’m wondering if the pressure is too high?
The door post information says around 33psi if four people are up for a thrill of a b58.
 

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The pressures quote on the door panel are for 20ºC so if you set them around this time of year they should be roughly right. You can adjust for temp when setting in colder or hotter condition. I think the adjustment factor its roughly 0.1bar per 10ºC which is roughly 1.5psi, so if you are setting temps on a freezing cold day at 0ºC, you set ~3psi less than on a 20ºC summers day, and on those days when the mercury hits 30ºC set a psi or 2 more.
 

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I believe 'cold' pressures to mean before you've turned a wheel. This could be -5°C in winter, or 30°C in summer.

I adjust mine to 34psi before setting off, all year round. They always increase about 2psi on my commute.

I wouldn't recommend setting them 3psi low in winter personally, I'm not convinced that's correct at all.
 

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I just quoted Marco to argue against Marco because I am watching rugby 7s while posting. Bad idea. There is logic and science in what I posted but I can’t elaborate more now other than 30psi at 0deg is the same amount of air in the tyre as 33psi at 20deg.

oh and note Marco, Porsche show a table of pressure corrections vs temp in their user manual. Or at least used to. You might see this when yours finally arrives!
 

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Tire pressures are ALWAYS, measured cold and one the reason for this is ambient temperature is hard to measure accurately, (as an example TP at 40degs should be xyz, so have your thermometer ready LOL) and also as AIR expands or contracts depending on temperature (except nitrogen filled, which is a different argument)

Cold is really relative, what is your usual ambiant air temp, 30deg's , -4, 102 ?

COLD tire pressure simple means "un-driven" tire pressure in a garage or in the shade is different on a a car standing outside in a heatwave,

I have Always done the below (when doing my monthly maintenance) I have the car on the drive and check the tire pressure in the morning over night.
OR if I must do a tire check after driving, after leaving the car parked for 3 hours at least,

The door jamb tire pressure is before driving, it also not an exact science you've probably got around 3 PSI either way.
Your really looking at not over or under inflating a tire. IF said tire is lets say 35psi...

that's 32-38 psi, that's quite a big range. You will find checking tire PSI's in winter are different than in summer. (assuming you have no leaks)
TBTH it's best guess, assuming your tire gauge is NOT a professionally calibrated one, your measurement is going to be quite out anyway.

And that crap they have in the BMW to give you an indication, is so outta wack I don't check it. It's ONLY good to monitor a flat or dramatic loss of preassure.

Accurate TP is really only an issue if you track or race

HTH


Hi guys
Someone please help.
I’ve always but under the impression you set your tyre pressures when the wheel is cold.
But after having the display on the dash telling us each wheel temperature and pressure. Obviously once the tyre becomes hot the pressure starts going through the roof.
Is it best to set the pressure once the tyre is up to a nominal 20 degree or so.
Running 19inch wheels on my m240 and currently just change the tyres to the Kumho non run flats from the Pirelli o zero which came with the wheels at purchase. Btw it’s a much softer ride but feels a little more yawning at high speed, which is why I’m wondering if the pressure is too high?
The door post information says around 33psi if four people are up for a thrill of a b58.
 
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The corrections rely on you having proper calibrated equipment and thermometers. Most Porsche drivers are not doing that except enthusiasts and even then most don't even check there brake lights and indicators let alone there TP's before driving off.



oh and note Marco, Porsche show a table of pressure corrections vs temp in their user manual. Or at least used to. You might see this when yours finally arrives!
 

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Loving the nonsense lads. If you haven’t got an accurate type presume gauge, buy one. How do you ‘ALWAYS MEASURE COLD’, when the temp isn’t? You need to compensate. And as for the tyre temp, your car tells you. Or if it doesn’t look at a weather app. It’s not something only race teams have access to.

If you cant work out the correction then set what you like. It won’t make much difference. It only matters when 10s of degrees are involved, but if you are putting in the same 34psi when it is -5deg and 35deg then you are doing it wrong. It’s specified for 20deg.
 

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I just quoted Marco to argue against Marco because I am watching rugby 7s while posting. Bad idea. There is logic and science in what I posted but I can’t elaborate more now other than 30psi at 0deg is the same amount of air in the tyre as 33psi at 20deg.
It is exacly the same number of air molecules, if that's what you mean? However, at 0deg/30psi, it's unable to support the same amount of weight, as it's less energetic. In fact, it will support approximately 3 lbs less, per square inch.

As your vehicle weight obviously doesn't decrese with temperature, you need to add more air as temps drop to make sure the tyre has the correct performance, feel, and footprint size. A lack of pressure = a larger contact patch = increased likelihood of aquaplaning (and wobbly handling).
 

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It is exacly the same number of air molecules, if that's what you mean? However, at 0deg/30psi, it's unable to support the same amount of weight, as it's less energetic. In fact, it will support approximately 3 lbs less, per square inch.

As your vehicle weight obviously doesn't decrese with temperature, you need to add more air as temps drop to make sure the tyre has the correct performance, feel, and footprint size. A lack of pressure = a larger contact patch = increased likelihood of aquaplaning (and wobbly handling).
This is true but it ignores the fact that in use, the tyre temp rises considerably and quickly so your 34psi set at -5º resting temp for instance means that when the tyre gets up to its 20-30º working temp, you are then at more like 38psi which is maybe too much for normal road use.

We are splitting hairs though, since I agree that for the majority of the time, setting what is on the door wont cause too many problems,
 
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