Most likely your new tires are also P-tires with reference-pressure 35 or 36 psi.
The 50 psi then is the maximum allowed cold pressure.
The difference between both is used in the official system, to highen up the reference-pressure for speed and camber angle, with a system depending on speedcode of tire.
For the reference-pressure and -speed ( 160kmph/99mph) the maxload is calculated by tiremakers, and put on sidewall.
So its a standard not calculated advice pressure that 35 psi.
Probably you can have for these oversised tires even about 25 psi safe pressure, so tires wont overheat, driving 99mph.
I can make a pressure/axleload list for you, with my determined extra safe formula and system, and gives 90% of the loadcapacity for 99mph.
Determined that to give max reserve, with still acceptable comfort and gripp.
Then you " ONLY" have to determine the axleloads in your use acurate, the most tricky part in it all.
If carmajer calculates the recomended pressure, he uses the GAWR, and mostly max technical carspeed for that.
Then only when standing still, you can put about 10 psi higher pressure to preven flatt spots, but they dissapear by themselfes on a healty tire, after 15 minutes of driving.
Need next of tire for the list, can be read from sidewall mostly.
1. Maximum load or loadindex
2. Kind of tire to determine that reference-pressure.
3. speedcode would be nice