Angryinch

The door jam sticker says 30/35psi on my SRS.

The dealer has the tires at this pressure cold. During sport driving I am seeing 35/40psi or roughly a 5psi gain to hot.


Does the manual say a different psi vs the door sticker? (I haven’t looked at the manual in the car yet)

Do you set your tires lower so they heat up to the door sticker psi or is that only for cold tires?

TRZ06

The values they give you on the door are COLD pressures. However, that is also just a guideline as COLD pressure is a moving target. Tire pressure varies by 1 PSI per 10 degrees. I use 60 degrees as my "standard temp." and reference point.

These cars are sensitive to tire pressure changes and I tend to be ****, so once I have my target cold temps based on 60 degrees, I can convert to that target by using .1 PSI per 1 degree. So for example if my target is 28 PSI COLD @ 60 degrees and I take my reading at 70 degrees, then I know my pressure should read 29 PSI.

I have a mini digital temp gauge that I have next to where I park my car and always take the reading in the AM before the sun can throw things out of whack. I also use a digital high quality calibrated tire pressure gauge that measures in .1 PSI intervals.

Tires also lose about .1 PSI every one to two days.

Like I said, I am super **** about it and keep my pressures at my target so my car feels the same every time I drive it. Believe or not, I can tell a difference of .1 PSI, it's subtle, but I can tell.

Sorry, overly complicated response to a simple question, but I'm bored this morning.

Cheers

TXshaggy

My April build shows 30/34 cold tire pressure on door jam.

Pretty sure if you use the Tire Pressure — Fill Info that is supposed to be temperature compensated.

Start there and move up/down for comfort and handling.

Load the Porsche App. Entire OM is in the app

Angryinch

Ambient temps are 25-30c. This is highway speeds on a rally.

The car feels a bit finicky when the tires get hot and this temp. Maybe it’s in my head…

Cold I am 30/35c.

should I drop a bit of pressure??

TXshaggy

Look at the tire fill data and adjust accordingly...

OM says not to use the raw TPMS data.

ExMB

Was this taken directly at the end of the rally?


Per the OM cold pressure is referenced to 68F/20C. 25.5C is about 78F. Static pressure should only be 31/36 at that temp. This looks more than smooth highway speed driving. It almost looks like the tires experienced a lot of turns as well as lots of braking; i.e. actual tire temps will be lots higher than OAT.

Angryinch

This was 150kmh+++ through mountain roads, hard corners, very hard braking and accel.

ExMB

In that case you should've started tire pressure way below "cold pressures" as shown on door sticker. I believe this to be referenced in numerous posts on here.

IanY

The cold PSI recommendations assume 'normal' street driving. No one in their right mind would use the cold PSI recommendations and take the car to the track and not adjust their pressures.

Hard driving on public roads depends on how hard you are driving. If your tyres are frequently reaching 42PSI during every trip, then you should drop your cold pressures. But if it was just a one off rally event, then I would get out and deflate half way through the rally to the correct pressure (like you would at the track), and then re-inflate at the end of the event.

Angryinch

Thank you. This I did not know, to adjust pressure if getting too high during hard driving.

Ambient was pretty high today and we were pushing pretty hard. I am typically seeing 5psi gain during most driving.

Should I knock cold pressure down 3 psi to give the tires more room for heat???

Reedy

Door card pressures are the target pressures at operating temperature. If you are using N spec factory homologated tyres then that is the target pressure you want the tyres to settle at under all conditions. Always. Door card pressures are the point where the contact patch is maximised.

Source was the chief tyre guy for Dunlop/Goodyear on a private call we had as part of our Tarmac Rally team sponsorship (We ran N spec Supercar R and RS). The next most important part according to him was to maintain the split between front/rear, if tyres are a little over/underpressured that's ok as long as you keep the 3-4 PSI difference front to rear.

On the road there is no real harm in running them a little higher but anything above the door card pressures and lap times fall off a cliff for me.

So we know what the factory and OEM tyre engineers recommend, then we get Manthey Racing who as far as i'm concerned are the absolute authority on this matter and they recommend running quite a lot lower (They recommend 1.9 Bar front and 2.0 Bar rear, HOT Pressures at the track)

ExMB

With pressures that high in the rear you'll experience oversteer, be greasy on tracks like HHR and Bilsterberg..

What is Manthey's recommendation for tracks other than NOS? Those listed pressures require a very low starting pressure.

Reedy

I agree, the SRS door card some seem a little incongruent with other cars in the range with the rears being as high as they are but it's a pressure that's derived based off the cars weight and suspension springs and dampers that should give the best overall tyre life.

I don't know what Manthey recommend for other tracks but ideal pressures are pretty universal regardless of operating conditions. For fast lap times, as low as you can get away with is generally the rule of thumb.

All of my personal best lap times have been set with pressures at or about 0.1 Bar below door card pressures (2.0 / 2.3BAR on my car). NEVER above them. Running as low as Manthey recommends might give better lap times but it eats sidewalls and throws constant TMPS warnings.

Angryinch

This is good to know thanks guys! I will drop 3-5 psi cold and see how it does from there.

cheers

ExMB

IMHO door card values have increased from GT4 and Spyder not because of wear but to improve mpg. Weight increase is immaterial here. My old GT4s (981 & 718) had 29/32 door cards and wore just fine.