Tires: PROPER TIRE PRESSURE, proper tire pressure, load index

Question
I have Nitto 305/45r22 tires on my f150.  Max pressure on tire reads 50psi.  What should I have the pressure at for best mileage/performance.  Currently they are all at 38 psi.

Answer
Kevin,

In order to answer your question, I need to know more about the vehicle the tires are going on.  The load and suspension play a large role in mileage and performance.

And the easiest way to sort this all out is to set up the new tires to carry the same load as the original tires on the vehicle.  So I need the information from the vehicle placard.

If I remember correctly, Ford puts the placard on the driver's door frame near the bottom.  What I need is the original tire size and the pressure for that size.  be sure to include the letters the are in front (and sometimes behind) the size.  Plus it would be helpful to have the Load Index from both the original tire size and the new ones.