Speed wobbles occur when moving at high speed on a skateboard. It is similar to fishtailing, wher you overcompensate for an error in guiding a vehicle. In skateboarding, speed wobbles occur because too much weight is put on one part of the deck for a split second, which makes the board dip to one side. Ther rider often unconciously compensates, and puts too much weight on the other side. During this, the board swerves back and forth, and unbalances the rider. Speed wobbles are usually caused by having loose trucks.