If you have a large capacity air tank, start at 40psi and like nextstep said, chalk the tires and if it rubs off the chalk lines on the sidewall at all, increase the psi until it stops. if you look around at everyones tires, someone will like be doing the same thing. I started with 45 in front and rear after getting my new tires and lowered until where they were rubbing on the shoulder where I wanted it. by the end of the day I had just 35 in the front and 32 in the rear. but then I have very stiff tires. you can go up to whatever the sidewall says is the max psi when the tire is cold. pressure will increase with temp of course. the MS is heavier and those BFGs are soft on the sidewall so you could start at 50/45 and work your way down. just don't forget to regulate the pressure before you drive home or you'll wear the center out of 'em.