depends on the weight of the bike w/ average rider. when i brought it home, I just rode it back without checking pressure. It seemed over 25 by touch, so it was good enough to get home. When I checked it the other day it was 26 front, 25 rear. Normal range for my bike (397lbs dry, no gas/coolant/oil, and about 420 lbs wet) it is 32psi front, 36 rear.
Tire pressure is vital on bikes because the tires are round and not flat. So low pressure - less curve - can't turn/lean well