I don't agree with the just run max on the tire. If it is not needed there is no reason to run it.
On my dually with 65PSI (RECOMMENDED PSI) the rear axle is rated for 9750 RAWR. My rear axle empty is 3300#. Loaded with my camper ready to go the rear axle weighs 7200#. So with the math I have 2550# of reserve capacity on the rear axle with 65PSI. Why would I need to run 80PSI?
If I raise my rear tires to 80PSI than I would have 11332# of capacity on the rear axle. Each tire on my truck in dual setup is rated at 2833# at 80 PSI this equals the 11332# stated above. This would give me a 4132# more capacity on the rear axle. Why do I need that much?
Unless you are running over the RAWR on most duallys there is no reason to have 80 PSI in a dually. I'm talking on the 3500/3500 series not the 450/550 with 19.5s.
If you are running a SWR than your RAWR is rated at 80 PSI. Most SRW with a camper are going to have to run the 80 PSI.
I would follow what the tire manufacturers have on their load charts. They have a little more experience than we do with their tires. Run what is recommended + a little more just for comfort reasons plus that is the minimum to carry the weight but just because it states 80 PSI does not mean that is what you have to run. That is the tire manufacturers have stated that it the MAX tire pressure and the given rated weight the tire can carry at that PSI. It is not saying that is what you must run.
For the fellows with SRW do you run 80 PSI even if you are running around empty most of the time? On my SRW when I was empty and not on a trip and just unloaded for a few days I would lower the rears to around 60 to 65 unless I was going to carry a load.
Take a look at CapriRacer link he has in his signature. I did and he happens to be a tire engineer. I think what he has written is well worth the read and to heed his advice. The guy has made a living at doing this for over 30 years.
This is IMO
