How do I know when my tires need to be rotated?
Courtesy of howstuffworks.com

Tire rotation is one of the easiest auto maintenance tasks to accomplish, but it's very important. Done properly, it can extend the life of your tires, improve your gas mileage and ensure that your car handles in a steady and predictable manner when you need to make a sudden turn or stop. Of course, when we talk about tire rotation, we don't mean the rotation of the tires around the axles when the car is in motion -- we're talking about moving the tires to different locations around the car so that they wear evenly.