As Pigheaded Dutch Selfdeclared Tyrepressure-specialist I have a different opinion about it.
The 50 psi maximum cold pressure, written on sidewall of many normal car tires and XL/reinforced/Extraload, is cold pressure and the rising of pressure by rising of temperature in tire, is included in the advice.

On American RV forum I once read from one who did much tyre work, that tyres are tested to can stand 2 to 3 times the pressure needed for maximum load wich is lower then that 50 psi max cold.
On LT tyres ( Lighttruck) and Trucktires they give this pressure mostly like this " maximum load xxxx kg/lbs AT yyy psi/kPa ( cold)", thats why I will call it furtheron the AT-pressure .
Normal car tires ( standard load=SL) and XL// give as exeption on sidewall the maximum allowed cold pressure ( 44 or 50 psi or XL sometimes 60psi) but the AT pressure is SL USAsystem 35psi and EUR system 36psi with exeptions to lower, for XL// AT USA 41 psi and EUR 42psi with exeptions.

So filling to 50 psi should not give tyre-damage by itself.
What mostly does the damage to the tyre is using to low pressure.
Then the tire deflects to much so produces to much heat in the rubber wich hardens it and crackes in next bendings so deflections.
Realise that at about 50m/80km/h every segment of the tyre deflects and flexes back about 10 times a second, wich produces heat .
Once the damage is done by to high temperature of rubber, and filled with higher pressure, the tyre damages quicker and you can wayt for a blowing tyre. And then the high pressure gets the blame , while in fact the to low pressure did the damage.

I think most cars in your country have pretty oversised tyres wich allow a low pressure , mayby even as low as 20 psi, and then this overheating still wont happen. But offroad tyres have often large profile-blocks that cover a part of sidewall, wich make them produce more heat at critical rings of tyre, so the maximum load given on sidewall is to high given by tyremaker, they give same maxload as a road tire with no profile blocks covering the sidewall.
This last makes that you would need a higher pressure to give lesser deflection so lesser heatproduction.
My estimation is that you should lower the maximum load of such a tyre by even 20% or lower the Loadindex with 8 LI steps.

This all means that you need higher pressure but not as high as 50 psi.
But this 50 psi cold is not bad for the tire if its filled from the beginning.
Only puctures can get sooner, and comfort and gripp is bad, but then blowing tyre by overheating wont happen.
Critical rings of tyre are where sidewall goes over to treath, there the isolation is more by the thicker rubber and the rubber can reach a higher temp wich does the damage. Then treath seperation is often seen.

will give self made picture of the offroad tires to show what I mean. One combined on/off-road and an even more ofroad tyre, to show what I mean with the large profile blocks, seen pictures about them tearing apart yust round the profile blocks at the thinner part of sidewall.

I promesed to translate my document about that filling cartires with normal air is better then with nitrogen.
Now here it is but also atachtment .

Filling car tires with normal air is better then with Nitrogen.
A. Oxygen, which makes 21% of normal outside air, in volume absorbs more energy to rise a degree in temperature then Nitrogen.
Difference is only 1% , but in selling argument is sometimes mentioned in energy/ mass so Joule/kg.degr. Kelvin and there Nitrogen wins by 13 % . Tires though are filled with a certain volume so that counts .
This selling argument can be de-myth simply by the fact that its untrue.

B. Water in a tire transports the heat more then dry air or Nitrogen-filling ( which is by its production process free of water).
Not for no reason water is used in central heating and cooling system of cars as main substance.
The tire inside will have lower temperature which is better for cooling down the important spots of the tire wich have to keep a low enough temperature to prevent hardening and damage in next bending of those parts.
When incidentally the tire inside gets hotter ( sunshine on tire or severe braking, or high ambient temperature) more water goes over to gas wich highens the pressure inside the tire more then dry gas. Also then more water as gas in tire so even better cooling.
So advantage of water is 2 ways when needed, better cooling and lesser heat production.
Disadvantages of water as oxidation only happen at outside . Tire specialists will confirm that when they remove a tire of the rim , the rim inside the tire is not corroded.

C. When a Truck, transporting flammable substance, is on fire, the little oxygen in a tire will , when exploding ,probably even kill the fire .
In tunnels experiments where done to kill the fire with air current , and it worked, despite the oxygen in it.

D. A normal car tire up to truck tire is not a race-car tire, for which a constant as high as possible contact area, so best grip , is needed to give half a second better round time.
For that reason they are filled with as dry as possible air or Nitrogen.
That this gives low lifetime is not important, and for a normal car tire it is.
Often blowing tires at racing, is seen there as collateral damage, but we don’t want that for normal car tires.

E. A car tire is also not a airplane- tire in which the water can freeze and when landing this can give misbalance , which can lead to tire-failure or accident, when suddenly going from zero to about 200m/h.
The water in a car tire does not freeze that often, and when it does and the car begins do drive , it begins slow and the misbalance is not a big problem . then pretty soon, certainly when on speed the ice is melted to water and problem will be gone.

F. When filled with normal air the user is aware of checking the tires regularly, which takes better care of a saver tire, because regularly filled up to the right pressure and optical checking of the tire .
The illusion that Nitrogen filling makes the tire to loose almost no pressure, which is often exaggerated to 5 times , while in real a poor 2 times and then only in the very beginning, makes the user less caring .
The tire also looses air when hitting pavement so temporary leak between edge of tire and rim, Filling with whatever gas-combination won’t prevent that.
This idea is even stronger when TMPS is used which is often inaccurate , so the user thinks to maintain the right pressure, while really riding with to low pressure for longer time, which can lead to tire damage. Aftermarket sensors for TMPS when screwed on the valve can give leakage trough hole where valve is placed , because of the bending of the valve by centrifugal forces at speed.

G. Filling with normal air is always possible, even with a bicycle- pump, is only to fill up so won’t take that long. When you keep driving with to low pressure , in order to find a place to fill with Nitrogen, you damage your tires. So just fill up with normal outside air, even when the tire is filled with Nitrogen. Then also you don’t need to have the tire refilled with pure Nitrogen by your tire specialist when at home again, not worth the trouble, and normal air is even better then nitrogen because of the water in it.

Not particularly dangerous because below the maximum pressure of a normal Standard load ( USA P-tire) tyre, wich is at minimum 44 psi.
but because that 35 psi is for maximum loaded car, and you probably dont drive maximum loaded , you can experience some discomfort by bumping, and nervous and verry light stearing.
Also the tire is easyer punctured at higher pressure.

But if you dont experiënce that all , keep using that 40 psi , always save for tire and livetime of tire.
Centre wear does not happen that fast for radial tires.

OK we go on.

The car makers use this formula , or gives a tyre maker the loads and speed, they want to have the pressure for, and let them calculate it for them.
Before 2000 in Europe there was given , a Normal advice for wich Car maker determined an Axle load for 3 persons and a little load , wich was for front wheel drive ( because of motor in front front heaviër) higher pressure then rear.
For fully loaded the MPAW/GAWR/MTA where used ( Maximum permisable axle weights) to fill in the formula , wich most is for rear more load so rear higher pressure.

In the 1990's rear was often put at maxloadpressure or even maximum pressure of tyre, to cover overloading , wich they discovered to happen often at rear.
America has always given only advice pressure for GAWR ( gross axle weight rating) but calculated wit a formula that lead to lower pressures so more deflection. As late as 2005 they stepped over to the calculation of European ETRTO , saying it was for globally using the same system, but left C-load/6PR and up at the old formula , still ask myself why.

After 2000 European car makers only gave for normal use 4 persons and load for wich MPAW where filled in , so what before that was for fully loaded. Heavy loaded advice is now for when towing and maxloadpressure of tyre is used behind.

By this chanche a lot of confusion game in.
But if you can produce the exact weighed loads on seperate tyres , for the situation you use , still a pressure can be calculated for that , wich is for 99% of use only 2 persons and a little load ,and so most likely front higher pressure then behind, yust as the old normal advice.

I now use for that my own universal formula with my own settings, to idea of an American IR who wrote an article about an alternative way of calculating and mentions the names Padua and Rhine, and compares it to the universal used formula of tyre makers with their different used powers in it in Europe and America. Will give the link for those who interests it , but be ware its a long story .
http://www.dawsengineering.com/linked_files/tirepressureatreducedloads.pdf

The difference between maxload- and maximum-pressure is used to high up the maxloadpressure before putting in the formula , for speed with a system depending on speedcode , and for alighnment ( camber-angle wheels like this on the ( imaginary axle) /-\ )
On Standard load and XL// tyres only maximum pressure is given , from C-load and up rule is maxloadpressure given , so there maximum pressure is higher . Determined it once from a PDF of Semperit ( continental) that maxpress= 1.4 X maxloadpressure.

To be continued if wanted

Registered to react to this topic.
Google for tire/tyre-pressure a lot because I call myself tyre-pressure specialist nowadays.
Began on Dutch Camperforum with an article because I got hold of the formula used for it by the European Tyre makers.
But in time gathered a lot information about the different ways of calculation, maximum load of tyres for different maximum speeds, and the difference between maximum pressure and maxloadpressure/AT-pressure/reference-pressure/ pressure needed for the maximum load.

The goal of tyre/pressure advice is to give the tyre a deflection so the bending of the rubber does not generate more heat on important spots ( or beter rings) then it can cool down between the deflections, and those rings dont get higher temperature then about 130degr C/??F.
A tire at 80 km/50m/h rotates about 10 times a second and every segment of it deflects and flexes back by that 10 times a second.

What tyre makers give on sidewall is the maximum load to carry at the pressure needed for the maximum load up to maximum speed of tyre or if lower 160km/99m/h. Then even 20 times a second rotation of tyre.

The goal of the calculation for lower loads is to give the tyre the same deflection over the whole range of pressure/load combinations, and by that the same heat generation wich it can cool down at the speed between teh deflections.

also saw here the different maximum pressures mentioned.
But this is not the maxloadpressure .
Here a small list.
Normal car tyre/standard load > maxloadpressure 2.5 bar/36 psi with exeptions to lower in European system. American system always 35psi/2,4 bar.
XL/Extraload/Reinforced tyres > maxl.pr. 2.9bar/42psi with exeptions 2.8/41 and 3.0/44. USA always 41 psi/2.8 bar.
C-load/6 PR ( for Plyrating) > maxl.Pr. 3,8bar/55 psi . USA 50 psi/ 3.4 bar.
D-load/8PR > maxloadpressure 4.5bar/65 psi or 4.75/69 or 4.8/70. USA only 65 psi/4.5 bar.
and so on, but for American TRA system a bit different.

And the lesson for today for Clemz85
PSI stands for Pounds per Squaire Inch. Edit : already saw this question answered.

I dare to state that Normal air filling with a bit of liquid water in it is better then to fill with dry air or Nitrogen for normal car tyres.
Already made a Dutch document for it and will translate it to English in time.
And Nitrogen needs about the same energy to heat up a degree as air in vollume . Selling arguments for Nitrogen sometimes mention Nitrogen more , but this is in mass .
for any gas pressure rises the same at a sertain temperature rising.


So you see there is much more to write .