Goodyear has the load/inflation charts on their website for most of the sizes of tires they sell. However, LT275/65R20 is a new size for them and they don't have it in their table yet. They do have LT275/65R18, which is a much more common size for 2005-up PSDs.
http://www.goodyear.com/truck/pdf/da...dInflation.pdf
However, any brand of load/inflation table that includes that size will be right. The tables come from TRA, not from the tire companies. I suspected Toyo would have it on their site, but no luck there either.
I found an old TRA table on the website of the Rubber Manufacturers' Assn (RMA). It's from 2004, but it includes the LT275/65R20E on page 14 of 23 in the link below:
https://www.rma.org/getfile.cfm?ID=606&type=publication.
Here's the table for LT275/65R20E tires mounted on single (not dually) axles:
PSI . Max weight
--- . -------
35 . 2,080
40 . 2,280
45 . 2,475
50 . 2,680
55 . 2,850
60 . 3,030
65 . 3,195
70 . 3,375
75 . 3,540
80 . 3,750
About 50 PSI front and 65 PSI rear is about the most inflation you should ever need if you don't overload your pickup. That's enough for about 11,500 GVW. And if you have more than 11,500 pounds on the 4 tires of an F-350 SRW, you're overloaded. And if you have an F-250, then you're severely overloaded.
When unloaded, you need about 45 front and 35 or 40 rear. More than that and the center of the tire will wear off fast, and the ride of the truck goes towards the empty-dumptruck ride. 65 front and 80 rear is insane on an empty PSD.
Adjusting the PSI is a PITA if you switch from loaded to unloaded often. But I keep a good air compressor at the house, and adjust mine as necessary. I usually air them down for unloaded only when I know I'll be driving a lot of miles unloaded before I tie onto another trailer.
