I took my toyo's down to 11 at barnwell mountain last week; they did excellent

 

I always air down. It makes a huge difference. It is well worth the extra time it takes to air down and air back up at the end of the ride. Works best in mud and on rocks. I air down to 15 and i run 35x12.5's BFG km's.

There are other threads about this but i figured i would throw it in here also. To air down buy the Currie EZ deflator. It makes airing down really easy and keeps all 4 tires the same. And is only $30.
http://www.4wd.com/productdetails.aspx?partID=4906

 

I air down, but not as low as most people since I'm afraid of popping a bead. I don't go any lower than 19 psi with my 35" cooper STTs.

 

Trust me it was a huge diff im airing down for now on way better ride

 

So I should be airing down to between 15-20psi on 35x12.5 Xterrains on 15x8 non beadlock rims??

 

I've had my stock Rubi down to 7 PSI in the deep sand of Silverlake MI and had no problems comming off the bead - KY

 

I go down from 29 to 19,

Red

 

I normally go down to 12-18 psi depending on the type of trails. Better traction and a much softer ride.

Front tire flattened out creating larger contact patch




Rear tire contouring to the rock surface creating more traction

 

Yes, usually to around either side of 15psi depending on terrain.