ity will depend on many things, best stick it in the middle range of about 4-5 PSI, and adjust if needed
some trails hard hard and fast, some wet spots, some more tricky where airing down is a plus
but at higher speeds them low air will get wheels damaged on rock edges, or poor handling
all maybe comes down to HOW fast you ride or slow too!
tree's here are just starting to show color changes, so should be doing the same there if not