Tire Pressure for very rocky conditions?

First of all, there are lots of numbers in between 14 and 20 [like 16]. There are also lots of different kinds of rocks - sharp rocks, round rocks, loose rocks , etc. There are lots of different riding styles in rocks - blast through - finesse through - wheelie through. There are lots of different tires--some with very stiff sidewalls [Cheng Shin, Kenda, Maxxis, IRC VE33]and some just the opposite --and-- lots of different weights of inner tubes from "standard" to "extra heavy duty". Finally, there are different suspension settings that will affect how the tire reacts to the terrain. Here in the rocky mountains I get by with 16 psi just fine but use the heavier tubes, the Ve33 tire, a revalved front & rear suspension --and I weigh 125lbs. If youweigh 225 you're going to have to add a bit more air. You simply have to experiment to find what works just for you and the way you ride.

I weigh 200lbs and use a Michelin S12 with heavy duty tubes. I usually run 12psi and never had a flat, this is in "rocky" New England.

20.......holy cow that would beat me to death! I never use more than 14lbs. It has to be really rocky to even use that for me. I switched back to the 100/100 and like it better after many 110/100's.