It's funny you should ask. I was just out on a walk and thinking I could update my opinions on the tires, now that we've done two extended trips. So far, so good. Theoretically we have another half inch of clearance. I can't tell any difference between the old tires and new, except our gas mileage has dropped a bit. But then our new tires are 31.7" diameter, and worn tires 30.0", which is 6% difference that our odometer doesn't know about. I'll need more time to comment on gas mileage.
On the pressure chart: I couldn't find any guidance on pressure depending on weight, except the capacity of the tires from the
Tire and Rim Association that Toyo has online.
The boxed-in numbers are from the TRA charts. Then I doubled that for axle weight (the line below).
Then I hemmed and hawed how to use that for the weight in our truck. The manufacturer says to use 30 psi in all four tires, and they seem to think that's ok whether the rear axle is at 2000 lb empty (I weighed it), or 2800 lb full (truck at max capacity). The front axle with two people was 2700 lb, pretty close. Perhaps Toyota wanted to keep it simple with just one pressure, I don't know.
Anyway, if you draw the lines on a graph (see
post #2), it's pretty linear. I calculated at 2700 lb with the stock tires at 30 psi, there was a safety factor of 152%. The method of selecting tire pressure for E rated vs. P rated seems to be based on equivalent load capacity, so using the same safety factor kinda makes sense.
The bottom line in the spreadsheet shows the axle weights by derating with a 152% safety factor (i.e., dividing by 1.52). This is my current best guess on what pressure to use for axle weight. So I'm using 47 psi front axle, 67 psi rear axle.
(I used 45/65 psi on the previous stock size E-rated tires and had reasonable wear on all four tires of 56,000 miles, tires rotated every 5,000 miles). On our last trip we used 18 psi front, 25 psi rear on rough roads, a similar ratio front/rear as for pavement.
I'm not totally convinced this is a proper procedure, but it worked ok on our previous tires, and the tire bulge kinda "looks right". I never did a chalk test. I'm really not sure a chalk test makes sense.