Two different types of imbalance can be found on a wheel:
A correctly balanced wheel can rotate freely around its horizontal axis and is able to stop in every position. If there is a static imbalance, the spot on the wheel with the greatest mass is acted upon by gravity to deflect the wheel downward. Static imbalance always occurs in the center of the wheel and causes it to bounce while driving. The static imbalance can be compensated by applying wheel balance weights on the opposite side of the occurred imbalance.
Dynamic imbalance is caused by an asymmetric mass distribution inside and/or outside of the rim. The asymmetric mass distribution is only visible during movement when the forces work in different directions and cause the wheel to hop or wobble. To determine a dynamic imbalance the tire/wheel assemblies can be checked on a balancing machine. The dynamic imbalance can be compensated by applying wheel balance weights on the outer and inner side of the rim.