Manufacturers of passenger vehicles and light trucks determine this number based on he vehicle's design load limit, that is, the greatest amount of weight a vehicle can safely carry and the vehicle's tire size.The proper tire pressure for your vehicle is referred to as the "recommended cold inflation pressure."
Remember, the correct pressure for your tire is what the vehicle manufacturer has listed on the placard, NOT what is listed on the tire itself.
Because tires are designed to be used on more than one type of vehicle, tire manufacturers list the "maximum permissible inflation pressure" on the tire sidewall. This number is the greatest amount of air pressure that should ever be put in the tire under normal driving conditions.