4 weeks into the MT 255/85/17's and very happy. I am running them at 36/38 psi around town, and air down to 20-ish psi off road if needed.
I had this conversation with the MT engineer this week about tire pressure.
"Thanks for reaching out and for sharing your observations. You're spot on about the increase in tire pressure you're seeing on long drives, from 36-38 psi cold to 43-46 psi hot, is a completely normal result of the tire heating up from friction and flexing during driving. This 6-10 psi increase is expected, especially over a 6-hour trip and in warmer conditions, and the observed temperatures align with this. Also, since you've changed to a non-stock tire size, the original door placard pressure may not be applicable for optimal inflation with the new Baja Boss tires. To help you determine the proper cold inflation pressure for your setup and ensure optimal performance and tire life, could you please send us a picture of your vehicle's door tag? This will show us the stock tire size and original equipment inflation pressure, which we can use as a baseline to calculate the appropriate pressure for your new 255/85R17 Baja Boss tires.
To answer your question about bleeding air off and refilling them, that would be a big no-no. All tire pressures are determined with the tires cold to accommodate for thermal expansion due to increased pressure, even the max inflation pressure on the sidewall. If you lowered the pressure when they were hot, they would more than likely be overloaded, or you could develop wear issues or worse. They may also be much lower than they should be (if you are still running them at the door tag pressure) which further increases friction (the tire has more sheer force to overcome) which generates more heat, further exacerbating the pressure.
Happy to help! After reviewing your door tag information, the 43 and 49 psi numbers do carry over to this size as well, so everything looks great there. That said, the PSI increase is within range considering the temperatures you shared, so if you keep the tires at the door tag pressure (cold inflation pressure) there should be no cause for concern. Also, ensuring everything is in alignment and performing rotations at every 3,000-5,000 miles will help keep the wear even across all four tires."
I will still run them in the 36/38 psi range, but I will no longer worry when they get to the mid 40's on the highway. The tires are rated to 80 psi.