I recently changed out the "P" tires on my Ram 1500 to "LT" tires with an "e" load rate. The tires have a max pressure of 80psi
While just driving with no trailer, I'm using 40psi in the tires, but I'm curious what you guys think I should put in them while towing. Would 65psi be too much? Not enough"?
Your truck has a recommended tire pressure placard on the driver's door. That's a good starting point.
Beyond that, weigh the truck with the trailer attached and get the actual weight on each axle. If you can't weigh the truck, estimate the weight on each axle. Then look up the required inflation pressure in a tire load vs. inflation chart for your tire size. Just because a tire is rated to hold 80 PSI without damage doesn't mean you should use that much pressure unless the load requires it.
Like Gary said, 65 PSI is a good off the wall guess.
If you want to go further, Toyo Tires provides a very comprehensive
Tire Load and Inflation Guide including a
downloadable PDF giving load vs. inflation pressures for all of the tires they manufacture.
Two items of interest: First, the inflation tables are based on Tire and Rim Assn. reference charts so the information is valid across other brands.
Second, the inflation pressure for a given load stays the same,
regardless of the tire's load rating. Higher rated tires merely allow higher inflation pressures if the load requires them.
The pressure indicated on the TIRE is the manufactures recommended pressure. When swapping out the origanal tire recommended for the truck always use the pressure indicated on the tire, when towing you should be at 70 - 80psi loaded
I believe that running at half the recommended pressure, no matter what the load on your vehicle, will reduce the life of your tires, and could damage your sidewalls. That could create a problem when you are running under a load.
If "recommended pressure" is the maximum PSI indicated on the tire sidewall, that's wrong. The tire pressure should be matched to the load, as noted above. Note that in many cases the charts recommend as low as 35 PSI in an 80 PSI rated tire
if it's appropriate for the load.