A rotating system of mass is in dynamic balance when the rotation does not produce any resultant centrifugal force or couple. The system rotates without requiring the application of any external force or couple, other than that required to support its weight. If a system is initially unbalanced, to avoid the stress upon the bearings caused by the centrifugal couple, counterbalancing weights must be added. This is seen when a bicycle wheel gets buckled. The wheel will not rotate itself when stationary due to gravity as it is still statically balanced, but will not rotate smoothly as the centre of mass is to the side of the centre bearing. The spokes on a bike wheel need to be tuned in order to stop this and keep the wheel operating as efficiently as possible