From Discount Tire:
Inflation
Always inflate trailer tires to the maximum inflation indicated on the sidewall.
Check inflation when the tires are cool and have not been exposed to the sun.
If the tires are hot to the touch from operation, add three psi to the max inflation.
Underinflation is the number one cause of trailer tire failure.
Load Carrying Capacity
All tires must be identical in size for the tires to properly manage the weight of the trailer.
The combined capacity of the tires must equal or exceed the Gross Vehicle Weight (GVW) of the axle.
The combined capacity of all of the tires should exceed the loaded trailer weight by 20 percent.
If the actual weight is not available, use the trailer GVW. If a tire fails on a tandem axle trailer, you should replace both tires on that side. The remaining tire is likely to have been subjected to excessive loading.
If the tires are replaced with tires of larger diameter, the tongue height may need to be adjusted to maintain proper weight distribution.
I don't load my trailer to the max, but I air my tires to max psi.