I think Issac Newton, or one of his buddies, fiqured it out some time ago, it's something to do with teh effect water as on friction. . . .
I have run dirt bikes with and with out rim locks and I thought that running without them was fine until I rode through a stream one day and some water got between the tire and the rim. As rode out of the stream I thought my clutch had failed as when I opened the throttle, even very gently, the motor would rev but I wasn't getting any forward motion, a quick check confirmed the clutch was fine but the rear tire was flat and the valve stem was no where in sight.
Moral of the story:
High pressues and dry conditions = no problem
Medium pressures and dry conditions = should be OK but could be risky
Low pressures and wet conditions = puncture repair time