[jadatis]

Needed cold tirepressure is is to give tire a deflection warm that wont overheat any part of tire material, when driving the speed constantly, for wich it is determined.

For that load on tire and maximum speed used ( and wont go over for even a minute) is needed, and tiremakers organisations have a formula for that to calculate it, wich I got hold of end 2007, and went running with.

Maxload of personscartires is given for max 160kmph/99mph, but mostly rounded to the 100mph you read.

For higher speed, but who drives it, there is a system for highening up the reference- pressure of 42 psi for XL, you most likely have, before puting it in the base formula.

This " pigheaded Dutch selfdeclared tyrepressure specialist" now uses an other formula and system for speed, wich to my conclusions in time, comes closer to laws of nature.

So to answer your question next.
Give here your tire specifications, and I make you a cold pressure/ axleloadcapacity list, with build in maximum reserve, but still acceptable comfort and grip.
Need next.
1. Maxload or loadindex
2. Standard load ( AT 36 psi) or XL/ reinforced/ extraload ( AT 42 psi)
3. Speedcode, less important, shal be Q or above

Then give max used speed for the situation(s) , and give if wanted in psi or bar, kg or lbs.

Then you " ONLY'" have to determine the axleloads for the situation(s) 99% acurate, and search them back in my list for the needed cold pressure ( at 68 degr F/20 degr C ambiënt temperature).
The most tricky part in it all, and your responcibility.
And different axleloads give different pressures front and rear. Only driver front highest weight, fully loaded rear higher axleload so needed pressure.

The carmakers use GAWR's and 99 mph for comfort setting, and max technical carspeed for sports setting ( or whatever its called)
The the number of persons in car and luggage is also used for different settings.

Then there is difference of opinion between systems of what to use for the pressuresettings, and that gives the different pressures you read between car and app.