Handlebar slapping

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Knocking the handlebars , also known as kickback , is a dangerous phenomenon that occurs especially on light and heavily motorized motorcycles (e.g. sports motorcycles).

When accelerating strongly, especially on irregular surfaces (waves, potholes), the front wheel lifts off the road due to the dynamic wheel load distribution (not to be confused with the intentionally performed wheelie ). If the acceleration is reduced, the front wheel comes back on the road. Since the front wheel is turned out of the direction of movement of the motorcycle in the phase in which it is in the air, it is slightly inclined to the direction of travel when it hits the road. This means that the front wheel is suddenly turned sideways when it comes into contact with the road. For the driver, this can be felt as a sudden rotation of the fork and the handlebar around the steering axis until the steering angle is full. Depending on the damping of the front wheel suspension, this deflection oscillates for a longer or shorter period with a frequency of several Hertz. In the worst case, when the pendulum movement occurs with a resonance frequency of the front wheel suspension, it does not come to rest or comes to rest only very slowly, so that the handlebars hit from steering stop to steering stop for several seconds (so-called tank slapper , because the handlebar ends almost against the tank beat).

In contrast to the more harmless handlebar flutter, this phenomenon is extremely dangerous and often leads to a fall at high speed. The driver is usually complicit, as a tank slapper grips the entire motorcycle when the driver clings to the handlebars. Because of the suddenness of the occurrence and the very high forces involved, you need a secure, firm hold on the machine (even without a handlebar). In order to counteract a fall, if at all possible, you should slowly reduce your speed and let the handlebars loose as much as possible.

In the meantime, steering dampers or at least holding points for these are sometimes installed in affected motorcycles . A steering damper is a shock absorber attached between the handlebars and the frame , which dampens the sudden strong movement of the handlebars and thus prevents the handlebars from slapping.