I pump my up to 37 when it's about 60-70 degrees F outside when it's cold and not in the sun. If the tires is facing the sun, it will be higher. Driving, it gets up to 37-38 when driving in the winter, and 40-41 when driving in the summer. If the outside temps drop to freezing, it'll drop the air pressure down to 32 PSI until it gets warm up.