Tyre pressures dropped suddenly

[Evnoob]

Did you check that the tyre setting in the PCM corresponds to the tyres you actually have on the car?
And the pressure should be at 20 degrees C. For about every 10 degrees lower temperature the pressure would drop by 0.1 bar ( 1.5 psi??)

PCM, yes it does. The temp has varied between 0 and 10c over the last week and maybe varies by about that amount but the diff shown in the brackets is consistently much more than that, as shown.

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[Evnoob]

Are we sure the pluses in the deviation diagram don’t mean that’s how much you need to add that would make more sense perhaps?

 

[Scandinavian]

Are we sure the pluses in the deviation diagram don’t mean that’s how much you need to add that would make more sense perhaps?

Plus sign is pressure above the recommended pressure for sure, minus sign will give warnings. Easy to try if you have the car with the display active and you deflate a tyre a bit.

Have you checked the specific screen that only shows the pressure deviation. Call it up by pressing the tight scroll wheel when in TPMS mode. Also look at what is stated in the Good to Know app. See below.

There could of course be something wrong with your system, but your service agent should be able to check that quickly.

 

[kort]

on my car there is a full load setting and a not full load setting.
I topped off my tires today and while checking the PSI I turned off the full load setting and it shows the tires are up to +10 PSI.
so what exactly is a full load?

 

[ciaranob]

on my car there is a full load setting and a not full load setting.
I topped off my tires today and while checking the PSI I turned off the full load setting and it shows the tires are up to +10 PSI.
so what exactly is a full load?

Thinking simplistically I would assume full load is 4 passengers and possibly luggage - anything else not?

 

[Evnoob]

Thinking simplistically I would assume full load is 4 passengers and possibly luggage - anything else not?

Yes

Plus sign is pressure above the recommended pressure for sure, minus sign will give warnings. Easy to try if you have the car with the display active and you deflate a tyre a bit.

Have you checked the specific screen that only shows the pressure deviation. Call it up by pressing the tight scroll wheel when in TPMS mode. Also look at what is stated in the Good to Know app. See below.

There could of course be something wrong with your system, but your service agent should be able to check that quickly.

Fair call. In my professional experience I doubt it’s a problem with my specific car. For one thing it’s just been for the firmware upgrades and has started showing symptoms of poor testing in other areas, economy for one - which is an easy calculation.

I’m starting to suspect the maths is just wrong.

So whilst we should be able to rely on the car computer rather than some other chart I’m not convinced.

The weight, width, temperature and tyre compound should be available in a simple table to within a few psi. It’ll vary with environment and use, but it can’t be beyond the wit of mankind to tell me what tyre pressures I should inflate my tyres on a stock premium car!

And when I say “mankind”, whilst I’m grateful for all the well informed suggestions in this thread…I mean the manufacturer, because their numbers don’t add up.

 

[Evnoob]

Here’s another example where the numbers simply don’t add up, so I’m afraid I just don’t have confidence in the software. It’s a pretty poor show really. And I’d like Porsche to take notice

https://www.taycanforum.com/forum/threads/tyre-pressure.2262/

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