It really depends on what you are doing. Whenever I go to race or pull someone out, I run 5 PSI. For general cruising I run about 12 PSI. If I know I am going to be hitting a lot of bowls, I run 15. At 15 PSI I can crank the steering wheel to the lock at 45 and I have only rolled a bead once at 15 PSI. YJ's don't like air or whoops. So unless you hit the whoops at 45+ you better be crawling through them. With my RC 4" lift and rancho's set all the way firm, I get about 3-4 feet of air with no landing ramp before I start bottoming too hard. 1-2 feet won't hurt it, but check your u-joints before you head home if you get it off the ground. The most important part, don't let the axle hop if you are spinning the tires. If you drive in 2wd and the hole jeep starts to shudder, let off and engage 4wd. You let it hop to much and you'll blow the u-joints, or pull the slipyoke out the back of the t-case and exploder it.