Understanding your tire ratings 101...Yes, you need to air up to get full load capacity of the tire! What is it you can not understand! A reading comprehension problem, maybe! When a tire is marked (example to make it easier for you) max load 1984 at max pressure 44 psi, that does not mean that tire has 1984 load capability at 30 psi. If you can read the tire manufacturers charts, they will tell what the load capacity is at a lesser inflation.
Bottom line...a little common sense...air your tires up to handle the load, but do not exceed max pressure as marked on tire. I am taking the time to school you, so others don't take your wrong advise of just looking at the door sticker, when they need to air up to handle the increased load, such as 1,000 lbs of tongue wt.
Jerry