You are correct,
The mail delivery trucks, made by Grumman, powered by GM or Ford (depends on the year) say 50 psi on the fenders.
We use GY Wrangler tires and that is the max sidewall pressure.
The P.O. specified many years ago that all tires were to be inflated to max sidewall rating.
Reasons stated were;
Too many failures from under inflation
and, get this,
Fuel economy.
It took the gubmint millions of dollars (I don't have the actual report handy)
and a team of X-spurts
and two years
to come up with this maintenance procedure.
All they had to do was ask me.
Your tax dollars at werk.
Now if we could just get them to let us align the front end properly we could end the early retirement of the steering tires.
although they get recycled and sent back to us with recap tread on them then we put them on the rear of the trucks, where they live out their life in peas and hominy. Showing NO signs of premature wear, or center tread wear before edge tread wear.
Schultz out.