Everyone, there has been some outstanding analysis and discussion on this thread. Thank you!!
So we know that 30psi is the minimum to meet the rating. I prefer higher pressure for (1) more tire (not axle) load capacity margin and (2) less sidewall squirm, but not so much as to get poor steering or abnormal tire wear.
The TRA table for P275/55R20 goes up to 35psi, but that's for a 111-rated tire. My 117-rated tire has a sidewall max rating of 50psi, which is clearly too high.
So I think where this puts me is somewhere around 35psi to 40psi. Any further speculation will be of the armchair variety, and only experimentation (and perhaps IR measurement??) will yield further insight.
But further speculation is still appreciated. :) It's easier to come up with experiments while sitting in my La-Z-Boy versus dealing with a TV/TT in highway traffic.
