Tire pressure for raptor sd

Hey guys I just picked up a a 60" rsd. My yard is fairly rough. What is the lowest air pressure I can run without messing something up? The tires seem hard as a rock!

Mine rides like a washboard....I got my tire at 10lbs. which has helped some.The Flexi forks apparently work well but they cost@$239 for the pair.One thing I'm gonna try is using is a small inner tube under my seat.....I read somewhere on this forum that it really helps,positioning will be tricky as my gas tank is directly under the seat.We need some mods to solve this issue.