When a tire recommends 50 PSI max air pressure then you are usually good when you fill the tire to 35 PSI or 40 PSI.
My truck tires are a 50 PSI max pressure and I only run 35 PSI in the front and back tires which is good enough for me.
If I'm towing a trailer with a heavy load then I will inflate the rear tires to 40 PSI to help with the weight of the load on the trailer and truck.
But when the truck is empty or not pulling a trailer I just run the tires at 35 PSI which is good enough.
You don't want to under inflate your tires because the tires can overheat and when you over inflate the tires they can wear out faster.