Vehicle manufacturer says to inflate to 50 psi. Sidewall on existing tires have 50 psi listed as max.
The replacement Good Year tires have max of 65 psi on the sidewall.
I see that the opening post on this thread says to use the sidewall pressure. But I have always gone with the vehicle maker's suggestions which are often lower than the max tire rating. For example, my F-250 wants 65 psi in front and 80 in the rear.
Do I use the 65 max on the tire or with the vehicle manufacturer's 50 psi?"
So I said: Simple question but I can make the answer complex.
The MINIMUM inflation you need to run is what the Load Inflation tables show for the actual measured load on your tires.
Lacking the actual scale reading, we need to look at your RV certification label that identifies the MINIMUM inflation your trailer mfg recommends. This is based on the DOT requirement that the tires be capable of supporting the GAWR load as shown on the label.
RVIA (Recriational Vehicle Industry Association) in 2017 started to require a 10% Reserve Load (Load capability more than the GAWR minimum).
As a tire engineer, I come at the topic of trying to provide the best conditions to allow the tires to run the longest. As I cover in my this blog post, trailers place extreme shear forces that are 24% greater than similar forces experienced on motorhomes. This, IMO is the primary reason for tire life in trailer application being less than on motorhomes.
Also, you need to remember and understand that it is the air pressure, not the tire sidewall that supports the load. If you run the inflation used in LR-C tire in a LR-D tire, you will have no increase in load capacity so will gain nothing.
Having said all this I would suggest you run at least the certification label +10%. If you can run label +20% that should result in better durability.
See that wasn't too painful.