Maybe this topic was already discussed somewhere, But I couldn’t find a decent answer.

i am living in Germany. Of course different weather / temperature conditions than in some parts in the US

i am driving 3 different wheel setups on my Cayennes.

295 / 30 / 22
305 / 30 / 22
315 / 25 / 23

always when I need new tires, the shops using different air pressure. Looks like there is no “rule” except the sticker in the door frame. But this sticker is about the 20” setup.

i would like to hear your recommendation.

we are not talking about ride quality. I know , less tire , less comfort.

I am just asking because of safety reasons. I wrote already to Continental and Falken , but even here the advise is very different.

Both cars are Cayenne first generation. One has 450 HP and one has 521 HP

80 % highway driving
no off road

thank you very much!

 

Needed tyrepressure is all about to give the tire a deflection, so heatproduction a cycle, that wont overheat any part of tire-material, when driving the speed constantly, for wich its determined.

this "pigheaded Dutch selfdeclared tyre-pressure specialist " can make you cold pressure/axleloadcapacity list for your tires.

Then you "ONLY " have to determine the axleloads in your use 99% acurate, and search them back in my lists.
The most tricky part, and your responcibility.

When I make list for maximum reserve, with still acceptable comfort and gripp, I give 90% of calculated loadcapacity for max speed 160 kmph/99mph, wich you wont go over for even a minute.
but for Germany this is not realistic, on highway .

so need your hounust given max speed,wich you wont go over for even a minute.

But knowing all this, you mayby understand the different advices from profesionals.

Need from all sets of tyres next, read from sidewall.
1. Maximum load or loadindex
2. Standard load or XL/reinforced/Extraload to determine the reference-pressure. Most likely XL// AT 2,9 bar/42 psi.
3. Speedcode, less important, shall be Q or above, for wich maxload is calculated for 160 kmph.

So also give your max speed, and if wanted in bar or psi, kg or lbs.
You can also do it by mail, then write me at my hotmail.com adres with username jadatis( combine yourselfes, spamm-machines cant this way).
You can write in German, but I write back in english, because writing in German becomes a disaster " kousbousendeutch".

 

Best regards to Oranje. Sorry you couldn’t make it to the final :-( fans are amazing!!!

back to the tires

thank you very much for your detailed message.

the problem is going to start with the max speed you have asked me. As you know, we haven’t speed limits on many highways in Germany

j am not a racer and even if I drive 3 different V8 cars (the cayennes and Audi S5 ) I still care about environmental issues and fuel economy. But sometimes of course I am driving fast. Fast means temporary speed more than 230 Km/h
Temporary means more than one minute and less than 10 minutes nonstop .

I believed there is a PSI number suitable for any kind of speed. As I mention, I am driving more than 80 % highway with a average speed between 120 and 160

 

Then question is with what loads you drive 230+ kmph.
if alone in the car, axleweight rear is lower then with 4 passengers and trucks to the airport. But then you can decide not to drive faster then 160 kmph, but maybybyust then in a hurry so speed higher.

Can make for every of your 3 tires, a list with in front 90% for 160 kmph, and behind cold bar for for instance 240 kmph.
carmakers give nowadays often only recomended pressure for MTA ( max tzulassiges achselast ) and max technical carspeed.

Then you see that pressure for lower axleloads when driving only driver, can probably do for MTA behind when only 130 kmph.
But mind that fully loaded sometimes forbidden overloaded rear axle, wich needs higher pressure.

And that is what I mean with that determining the axleloads in your use, is the most tricky part.

 

If higher speed, more cycles a second, so more heatproduction.
cooling down stays about the same, so you need lesser deflection to give same heatproduction at that higher speed.
I determined a rulebof tumb system for speed, looked off from C- and truck-tyres,
Is for every 10 kmph/ 6.2 mph different speed , 1 loadindex-step different. Higher speed > lower loadindex, lower speed > higher loadindex .
gives for max 120 kmph 4 LI steps higher then for referencespeed 160 kmph, and for 240 kmph 8 LI steps lower.
That corrected maxload for that loadindex I use in my spreadsheet for making the list., and I can give the % to use of calculated loadcapacity.
but you could calculate lineair, not that bad , official calc gives lower pressure, and add reserve yourselves.

 

I appreciate your support very much. But the conditions under which I am driving are changing frequently. Amount of passengers is changing as so the load I am carrying with me. So I understand there is no „ one and only“ pressure number

 

Thats the problem, the profesionals you asked, also have.
they dont know how you use the car, and if to low adviced, and it gives overheating, and by that your tires blow or treath separates, they dont want to be held respocible.
and that gives all those different advices.

So in your use, you have to use pressures for the worst case scenario. Is axles fully loaded , rear mayby even overloaded and for max technical carspeed.
But you could mind the speeds a little, then lower can be enaugh.
that is with higher axleloads, reduce speed, dont race.

 

I run 38 F and 43 R on my 22x12 with 335/25 tires all the time, but I'm in the US so sustained speeds never really exceed 100 mph for very long.

 

thank you very much !