As already written, first you have to determine the real weights on axles or better even seperate tires ( or tirepair). often yudged wrong, so best is weighing.
Then you can even add 10% to that for reserve and unequal load R/L if axles weighed, and gripp and comfort still acceptable.
Then look up these in a pressure/loadcapacity-list.
I made extra save p/LC lists and added one in this post as atachment, for the 110 psi. Saver then the European made lists , and much saver then the USA made lists.
Look on tire for the maximum load or loadindex, then search that in the PDF I gave, and look in that line for the load yust above yours determined.
Look below or above for the pressure it needs.
you can find these lists in a map on my public map of one-drive that belongs to my hotmail-adress with username as in this forum ( jadatis).
Even a collection PDF of all the pressures ( loadranges), and given per tire, axle single and axle dual. The list I added is for per tire, so you have to devide by 2 for single axle and 4 for a dual axle.
Greatings from a Dutch Pigheaded Selfdeclared Tirepressure-specialist.