The proper air pressure for a car's tires can typically be found on a sticker inside the driver's side door or in the owner's manual. It is important to check the air pressure in your tires regularly and to adjust it as needed to ensure that your vehicle is operating at its best. Over- or under-inflated tires can affect the handling and safety of your car, so it's important to keep them at the correct pressure. It's a good idea to check the air pressure in your tires at least once a month, and to adjust it as needed to keep it at the correct level.