The recommended tire pressure for car tires is dependent on a combination of factors, including tire size, vehicle weight and the temperature. Modern cars mark the recommended tire pressure on a sticker or placard inside the driver's door and in the owner's manual.
Although tire manufacturers emboss the maximum cold PSI on the side wall of a tire, the maximum air pressure does not take into account vehicle weight. Drivers should always follow the vehicle manufacturer's recommendation when inflating tires. Firestone provides a tire pressure calculator on its website at FirestoneCompleteAutoCare.com. Drivers can select the vehicle year, make and model to see the factory-recommended PSI for front and rear tires, including standard and optional tire sizes. In general, larger tires must be inflated to a higher PSI.
Improper tire inflation adversely affects vehicle performance and safety. It can also cause uneven wear on the tire tread or destroy the tire. Overpressured tires develop excessive wear along the center of the tread. Underpressured tires develop worn shoulders and can also decrease fuel efficiency.
Temperature can greatly affect tire pressure and the flexibility of the rubber. Drivers should never inflate hot tires with cold air, as this can lead to inadvertently overpressuring a tire. Drivers should check tire pressure regularly, especially when there are rapid or extreme changes in outside air temperature.