montreal

I'm just wondering something, i just buy new tires Falken ST-Z01, on the side of the tire it's write 51psi max. and a guy who install it put 40psi.
He said that if i put less than 35psi, my handling and the tire life gonna affect.
I know normally it's 44psi max. for a normal tire and i put 32psi but now with 51psi max. how much i can put in there.

Right now i put 40psi at hot.
What do you think???