i usually keep 32 throughout. Nissan sedan
at 32 i feel, better agility. Tires are 215 something Nexen
Previously used to put 30/31 in front and 32 in rear. 30 and under, tyres seems a but deflated.
Moreover 32 is a safe bet, underinflation is dangerous due to excessive heat production via friction. The Max PSI stated on sidewall does not refer to the Max PSI you should have, it is what the Max PSI that particular Tyre can handle without danger.
The reference on the door side of vehicles is usually for the size and tyre provided, so if you tend to change the tyre, the Air pressure reference is not totally relative then.
Moreover low PSI gives more bodyroll, sluggish turning, increases the braking distance and load on the front shocks when you press the brakes due to more flex in rubber, although increases grip but generates more heat and is prone to damage. Anything upto 36 wont hurt, under 28 i suppose is pretty low, and i dont buy the tire pressure reference on local vehicles at all.
In summers the tire does heat up, and i suppose you might get an increase of 1 or 2 PSI in hot weather, so ill be keepin 30 or 31 then.