It's generally recommended to check the air pressure in your car's tires at least once a month and before long trips. You should also check the air pressure if you notice that your car is not handling or riding as smoothly as usual. If the air pressure is too low, it can cause the tires to wear out prematurely and make your car less fuel efficient. On the other hand, if the air pressure is too high, it can make the tires more susceptible to damage from hitting curbs or potholes.