What is the safe LT275/70R18 Toyo M/T psi?

I have a set of Toyo M/T LT275/70R18 and I wonder what is the right amount of psi I inflate the tires to. Is it 80 psi or 40 psi as on regular stock tires. I checked the psi just now and it read out to 50 psi to all tires. Being that it is on a 1-ton truck it's got me confused.