Tire pressure after buying

[magnitude]

So, safe to say that the dealer put in too much air and I should let some out, or do they know something that the app/car doesn’t?

21” Mission E wheels.

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[Jayyvr890]

I've always run a little higher pressures for better efficiency

 

[Archimedes]

Are those cold or hot pressures?

I run 38-39 cold all around.

In California, I believe there is a law that any car serviced at a dealership has to have the tires inflated to max recommended pressure before being returned to the customer. Dates back to the Firestone/Ford Explorer fiasco.

 

[miwim]

think those are full load pressure and your car probably set to partial load

 

[W1NGE]

So, safe to say that the dealer put in too much air and I should let some out, or do they know something that the app/car doesn’t?

21” Mission E wheels.

If these are the same wheels that were fitted at the factory then refer to the driver's door plate where the loading and pressures are recorded.

 

[f1eng]

So, safe to say that the dealer put in too much air and I should let some out, or do they know something that the app/car doesn’t?

21” Mission E wheels.

I correct my pressures whenever the display shows them out by more than 1 psi.

Tyre pressure is one of the first order parameters when setting up a racing car for grip, balance and life so I am maybe unusually anal about it.

It is all about getting a good contact patch shape (though on a F1 car lower is almost always better up to the point of getting damage).

Too low on a road car will lead to uneven wear and maybe structural damage.
Too high gives a reduced contact patch area so whilst it will offer lower rolling resistance it also offers lower grip - so your stopping distance in an emergency is longer, and may well be a false economy since they may well wear out unevenly and need replacing prematurely.

 

[whitex]

Full load/partial load makes a difference in expected values, as do different tires (winter/summer/all-season) and tire sizes. You can see the expected cold pressure for the tires you have on in the PCM. For my 20" all-seasons (factory tires actually) it expects 35 psi all around at half load. That said, I adjusted the cold pressure to the desired 35 on mine on cold tires at 40F, but the car would still show 1psi over, even when the tires were showing 34 psi (so 1 under). Fine, so I let 1 psi out of each tire, which finally started showing 0psi differential. Then a few days later the differential started showing +1psi again (for all tires). Somehow I doubt the Taycan pumped up its own tires, so it had to be the warmer weather we got very recently, but according to the manual the car should have compensated for the temperature already, which to me means that the temperature compensation is not very precise on this system.

 

[whitex]

If these are the same wheels that were fitted at the factory then refer to the driver's door plate where the loading and pressures are recorded.

Sadly, not true even only 2 months after delivery. Here are my expected pressures from the PCM for tires which came from the factory:

And here is the door jam sticker:

They are close to full load numbers (1 psi off for rears) but not the same, so either Porsche is loose in specifying parameters, or the OTA maintained software has the latest numbers, while my sticker, even though less than 4 months old (since production), is already out of date. Maybe they need to replace the sticker with e-paper screen (like e-readers) which can be updated over-the-air and whenever the tires are changed.

 

[SergeyIndy]

I was wondering what everyone goes by, the sticker or the PCM.
I go by the PCM as it has, to everyone's point, other dynamic impacting parameters per wheel size such as All-Season, Summer, etc. and Full vs. Partial. Our Cayenne even has another called Comfort which recommends lower pressure. Also, the other bit that I know of after driving a lot car that is for sale (still waiting on mine) is that they put the cars out to stand at max pressure for the tire, so when they let me have it (2022 Base for a 750 mile drive), the pressures were showing +10psi, so I had to deflate them to PCM values immediately.

 

[tchavei]

In case someone missed it (from the manual):

I guess it's more to give a general idea then use it to adjust tyre pressures?

 

[Sidicks]

What am I missing here?
- Front axle data suggests 38psi is the correct tyre pressure so both front tyres need to be reduced by 3psi
- Rear axle data suggests that left rear needs to be reduced by 4psi to 40psi but right rear needs to be reduced by 6psi to 38psi?!

 

[magnitude]

Rear axle data suggests that left rear needs to be reduced by 4psi to 40psi but right rear needs to be reduced by 6psi to 38psi?!

Oh wow. I didn’t even notice that. Yeah, what the hell?

 

[Hirschaj]

What am I missing here?
- Front axle data suggests 38psi is the correct tyre pressure so both front tyres need to be reduced by 3psi
- Rear axle data suggests that left rear needs to be reduced by 4psi to 40psi but right rear needs to be reduced by 6psi to 38psi?!

More bad software. Just run 39 on all 4 and call it a day.

 

[whitex]

In case someone missed it (from the manual):

I guess it's more to give a general idea then use it to adjust tyre pressures?

The pressures change with temperature, therefore should not be used to adjust, HOWEVER the pressure deviation is compensated for temperatures, and the manual states it should be used to adjust the pressure.

 

[whitex]

What am I missing here?
- Front axle data suggests 38psi is the correct tyre pressure so both front tyres need to be reduced by 3psi
- Rear axle data suggests that left rear needs to be reduced by 4psi to 40psi but right rear needs to be reduced by 6psi to 38psi?!

The current pressures are actual, not adjusted for temperatures, so the tires which are at exact desired pressures can show different values as their temps may differ. The pressure deviation is adjusted for temperature (according to the manual).

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