Tires can lose about 1 to 3 psi (pounds per square inch) of air pressure per month, translating to as much as 9 psi over three months. It might not sound like much. But trailer tires (bearing an ST designation), unlike passenger-car tires, are designed to operate at the maximum-rated psi, which you will find embossed on the sidewall, to maintain their load-carrying capacity. Underinflated trailer tires can also suffer sidewall damage and blowouts on the highway. Check your boat-trailer tires regularly with a quality tire-pressure gauge. Do it before you head out; the ratings are based on “cold psi,” which means the pressure before the air inside heats up from road use. Add pressure as needed.