I run them between 8-18 psi... and yeah.. sometimes they work... sometimes they dont. I have had experiences where I climb right up an obstacle... then next trip out I try again and make an ass of myself trying to get up and over the same thing... i think 12 psi is a good number for these tires.... it's all about how heavy of a load you're carrying... i think I'm gonna sell my mtrs... they're still really fresh... i don't daily it anymore so I can justify throwing some better wheeling tires on it.