I was driving to work yesterday and my car seemed low on air pressure. The car was driving ok and i stoped by a gas station on my way home and filled up the air on the driverside rear tire and on the way home i felt a vibration in the car. What could be causing this? It was only after i added more air to the tire that the car begin doing this. I had not driven the car in a week....don't know if that has any relavance.

Did your car come with perrelli's? If the car sat for a week you may have temporary flat spots, take it out and drive it on the highway for 15 minutes or so and it will go away. The reason I ask if the car came with Pzeros vs Michelins is they flat spot easier. Michelins are a better tire but they too can flat spot just not as easily as other brands. Hope this is he;lpful.