Tire balancing is pretty much what it sounds like. It compensates for the weight of the tire and wheel assembly after the tire is mounted. A wheel is out of balance when one area is heavier or lighter than the rest. That causes bouncing or wobbling, which can decrease treadwear, increase vibration and cause stress on your vehicle. The cure? Correction weights are added to counterbalance the tires.
Balancing a wheel is pretty cool process. Your mechanic uses a high-tech balancing machine to determine where the heavy spots are. Weights are then attached to the exterior or interior of the wheel to counteract centrifugal forces acting on the heavy areas when the wheel is turning. This will eliminate vertical bouncing and side-to-side wobble.