I air down on most trails/roads that are not smooth, my purpose is to make the ride a smooth as possible. I do not drive in sand or mud (there is none near where I live) so that is not a concern and I feel my current tires and the power of the Hemi will move me through or over almost anything. But on the longer rides it is nice to have a smooth ride and reduce the jaring as much as possible and for that reason I will air down to about 25Lbs of presure.