I just bought a 2010 F250 regular cab, long bed 4x4 with the 5.4l to tow my camper with my and my wifes Harleys in the back. In that configuration it handles great with the suggested tire pressure. How low can I go with the tire pressure when driving empty the rest of the time?

 

Place a chalk line across the tires and drive a short distance, maybe a block, then read the tires. Use the lowest pressure that still gives you uniform wear.

 

You should have tpms - which on my truck is set at 65psi.