When you did the weighing, first add 10% to the loads before searching back in pressure/loadcapacity lists. This is for pressure loss in time, unequall loading R/L, misreadings of pressure- and load-scales, incidental extra loading or loadshifting.
As long as you did not weigh, you will have to do with the Gross Axle Weight Ratings ( GAWR) mostly written on the same plate as the pressure advices , somewhere on the car. Then front only 5% adding ( because seldomly used to the GAWR) but back more reserve , depending on the GVWR, low 15% high 5%, because back is often even a bit overloaded, in combination with unequall loading R/L.
The tire specifications you can find on the sidewall of it, together with the DOT-code wich on one side also gives in 4 figures the production week .
Read from tires maximum load in kg or lbs, and the ,as it is called , reference-pressure( not the maximum pressure) mostly written like this on it, "maximum load xxxx lbs AT yyy PSI (cold).
When you have all this information you can look the loads with reserve , back in lists, but better in my made list, wich are saver, because lower loadcapacity for the pressure, wich gives the same deflection of tire at lower pressure/load combinations, and allowes to go verry low in the pressure.
open the USA map for America, and pick the PDF by the pressure .
Then in this list at front the loadindexes and belonging maximum load,
Search the one you have, and search the determined loads back to get the needed pressure above or beneath that.
I added as atachment to this post, 3 PDF's of 95,80 and 65 psi reference-pressure per tire. In the map there is more and also for per axle single and dual , so you dont have to devide yourselfes by 2 or 4 .
These lists are saver then the American list you find for LT and Truck tires, even saver then the European lists.
But I also made a RV tire-pressure calculator and put it in this map.
To use a spreadsheet, first download it by RIGHTclicking on it , then choose download from the dropdownbox. After Download and eventual virus-check, open it in Exell or Open Office Calc. If you have one of those programs on your computer it is automatically openen in them when clickked on the document, if the settings are right on your computer.
Spreadsheets also in XLS for older Excell versions.
Dont click Left on the spreadsheets, then they are opened in a simple excell programm in the browser, wich cant handle some things I used in most spreadsheets.
But if you cant figure it all out , give here the details, and I will do the calculations for you.
Greatings from a Piggheaded Dutchmen