Dynamic Imbalance: Occurs when there is unequal weight on one or both sides of the tyre/wheel assembly's lateral centerline, thus creating a side-to-side wobble or wheel shimmy.
Static Imbalance: Occurs when there is a heavy or light spot in the tyre so that the tyre won't roll evenly and the tyre and wheel undergoes an up-and-down motion.
If wheels are not balanced, the result could be uncomfortable driving, and premature Correctly balanced wheels help to eliminate vibration and avoid premature wear caused by an imbalance in the rotating wheel and tyre assembly.
Vibrations happen because of the structure of a wheel assembly. Two slightly imperfect units are joined to form one complete assembly, and there is usually uneven weight distribution - heavy spots cause the wheel to wobble from side to side.
This means that wheels need to be balanced using small weights that smooth out weight distribution and stop the vibration.
The first sign that your wheels may be out of balance is when your steering wheel starts to wobble above a certain speed. The light weight of modern cars means that they don't dampen down the vibrations caused by spinning wheels in the way that older, heavier vehicles could.