The correct tire pressure can be found either on the tire placard located on the driver/passenger door sill or comes with the tire. It is usually recommended to stick to the vehicle manufacturer specifications found on the placard, as these numbers are determined specifically for each car. The tire pressure can also vary based on the application like a highway or off-road driving requires different tire pressures for optimal performance. For highway driving, you must have your tire pressures set at the recommended psi, whereas for off-roading most people prefer lower tire pressure as that helps in gripping the uneven surface better. The tire pressure can also vary across the font and rear wheels and it is best to consult your owner's manual or tire placard for more info.