proxim2020 wrote:
The max cold PSI stamped on the side of the tire should never be exceeded. Once you've gone past the max sidewall, the tire is now overinflated. The tire will start to balloon or crown and you'll end up with a lot more wear in the center of the tire than the edges. There's a chance that the tire will suffer internal damage due to over pressurization. The max sidewall takes into account pressure changes due to temperature changes, but starting out 10 PSI beyond that mark could damage the tire.
As said before, the extra PSI recommendation applies when you're recommended PSI, for the load, is under the max sidewall. If you're towing between 65 - 70 mph then a better idea would be to get more appropriate tires. Switch to 75 mph ST tires or switch to LTs where speed won't be a problem.
I would strongly suggest going to LT tires, if you want to tow over 65 mph. Your F150 with the Max/Max packages should already have LT tires.
What size on your 5er 15" or 16", with about a 10,000# GVWR 16" LT running about 65 to 70 psi will do very well!