Rob:
I finally found a website for goodyear tires that has a tire inflation guide as you indicated (here
http://www.goodyearrvtires.com/pdfs/tire-care-guide.pdf )...page 9. You were right, it was difficult to find this information, and although you said many companies endorse it I had trouble finding even one.
For my tires ST205/75R14 it shows 50psi for 1760 lbs as my tire indicates, and the table shows that at 40psi a load of 1530 lbs....so 3520lbs at "max load", 3060 lbs at "flat." Everywhere I read read it has indicated that a tire with less than 80% of its maximum rated tire pressure indicated on the sidewall should be considered "FLAT" and the trailer should not be moved until the tire is fixed. Some where in between "max" and "flat" (some places use 6% down or 3lbs psi in my case) you run into the tire wear/irregular treadwear/reduced casing durability/fuel economy/handling/catastrophic tire failure issues. "Technically" at 20psi I would have over 2000 lb capacity with my tires according to the table, more than enough for my small trailer, although they would be pretty darn flat on the bottom portion of the tire.
I don't know the proper answer here, only throwing this information out for consideration. My trailer, which I have not weighed yet, is probably around 1200-1300 lbs. I know that if my tires are inflated to 50psi (3520 max load) I will get maximum tread wear, highest fuel economy, best "performance", supposedly best braking because of proper profile of rubber touching the road, and the least chance of catastrophic tire failure. Whereas at 40 psi (3060 max load) I will be "technically" running my tires "flat", get poorer mileage, reduced tread wear and tire life, poorer performance and braking, and run a much higher chance of catastrophic tire failure from heat/pressure build up...and a blowout towing a trailer at highway speeds, although I have not experienced it or seen it, I imagine has the potential to be not a pretty sight especially if you have a smaller tow vehicle like mine.
Is the "less pressure/smoother ride" worth it? Would I even notice a difference between 3520 vs 3060 max tire capacity with a 1300 lb trailer?
I honestly don't know!!! Will I try going from 50psi to 45 psi next year (1760>1640)...maybe. Will I go below 45psi...definitely no.
*When doing anything, if there exists no possibility of failure, then any feeling of success is diminished.
**The glass is neither half full nor half empty...it is simply twice as big as it needs to be.
***If at first you don't succeed, redefine success.
****When I die, I want to die like my grandfather, who died peacefully in his sleep. Not screaming like all the passengers in his car.