Hello new here and to the mountain biking world. Got my first bike after 22 years of not being anything on two wheels. Anyways I get it home and it has 29's on it and i inflate it to the max pressure on the side wall which is 40psi. I'm 6'4 250 and when I get on they look and feel under inflated?!? It handles like poo and takes bumps the same! Got off checked it and still 40 psi... Help!