When you get into oversized tires, wall thickness comes into play with differant manufactures. Adding aftermarket bumpers and body protection changes the vehicle weight. The following is a good practice when wanting to know the correct tire pressure to run.
-Wet driveway down
-Drive through getting tires wet
-Add or remove air until your tires are wet all the way across the tread pattern, this will let you know you are getting even tread wear.