The most important guideline when checking a vehicle's tire pressure is to know the tire manufacturer’s recommended pressure. The pressure recommendation for the front and rear tires may be different.
The recommended pressure measurements apply only to cold tires. Since the air in tires expands as the vehicle warms up, it is best to check tire pressure in the morning, or at least wait a few hours after the vehicle's last use. Add or release air until the tire reaches the desired tire pressure. Make sure not to over-inflate tires, as this can cause the tires to expand and fail when driving.