This is a rough guideline. The absolute number is irrelevant, finding a pressure that works, and then being able to both recognize the conditions and duplicate the appropriate pressure is what matters.
10psi and up = pavement pressure.
6-8psi = *very* hardpacked snow.
4-5psi = softer or less consistently packed snow.
2-3psi = deeper snow, when more flotation is needed. If you need this kind of
pressure, you'd probably be having more fun with skis on! But
sometimes you start a ride on hardpack and have an ambitious
objective, then it snows or blows and you have to dump air to keep
riding.
0-2psi = what I most often ride at, due to lots of light, dry snow and very little traffic.
