The recommended tire pressure for a vehicle is jointly determined by the vehicle manufacturer and tire manufacturer. The recommended tire pressure for your vehicle's tire combination can be found in your vehicle manual, on the inside of the fuel tank cap, or on the driver's door post.

Tire pressure affects many important aspects of vehicle performance, such as driving comfort, directional stability, steering and braking grip, as well as overall handling performance.

Driving vehicles with improper tire pressure can have adverse effects on these important characteristics.  

Generally speaking, tires lose one pound per square inch of pressure per month, so check the tire pressure before long-distance travel, and even check the spare tire.