I normally run 33-34 psi in my tires, which are filled with nitrogen (if that matters). Since the weather here in Charlottesville, VA has dropped (twenties to high teens at night) My tire sensors show 28 to 30 yet low tire warning does not come on. During cold weather, should I pump up pressures or leave them alone. When the weather warms during the day, say up into high 50's or mid 60's, the pressures seem to get back to normal. Suggestions?