Every revolution of the driving wheel and rods has side effects. The wheel cranks are—by necessity—not centered, so they add weight to one side of the wheel. The connecting rods add more weight. A counterbalance adds the same weight to the opposite side of the wheel. This leaves the wheel unbalanced at the quarter-turn between the crank and counterbalance. A wheel is stationary where it touches the rail, and it revolves at twice the locomotive's speed at its highest point. These factors cause "dynamic augmentation", a jerking motion that lifts the wheel from the rail and slams it back down.