I have noticed that the tire pressure on my car needs careful monitoring. I hadn't driven my car in a couple of months, and last week when I pulled onto the freeway I felt a definite vibration in the front end. I thought I had thrown a wheel weight or something, so I pulled off at the next exit and checked the tire pressure. All four were at least five pounds low, and I've driven less than a couple hundred miles since last checking them. Added air and the vibration went away.