My Tiger/Ram diesel 4×4 was a dually. Terrible traction sand or any soft terrain. I did the SRW conversion and installed HD wheels and tires for the 11,200 lbs it weighs.During my research for suitable wheels and tires, I contacted the manufacture Nitto. Rep. said what tire and load was I asking about. I told him, Ridge Grappler 305x65r 18 “F” rated for 3,900 lbs. and I have a 3,250 lb. load per back tire. He said, “never air down”, it would likely damage the internal plys. I was shocked, I said, I’ve been airing down my 4×4 tires on Jeeps and Toyotas for 40 years. He said the weight on those tires compared to their load capacity was minimal. Being the jackass that I am, I’ll still air down to try and self extract if stuck(hasn’t happened) but I would never run them that way. BTW, My Tiger is not an off road vehicle and I only use 4wd when 2by limited slip traction isn’t getting it. I have a Wrangler Rubicon on 37” M/T tires currently for off roading.I air them down to low teens.
BTW, the Nittos now have 50,000 plus miles on them and have a strong thread depth still. Probably go another 15,000 before any concern and I like to pull a tire out of service earlier than most.
Bottom Line, I say talk to the tire manufacture, then do what feels right to you haha
Thanks for the info….. yeah i wondered about the internal construction with a big load like ours…..