Speed wobble (tank slapper)

A speed wobble is a rapid oscillation of the front end in which the handlebars shake from side to side, sometimes hitting the tank (a 'tank slapper'). A slower, low-speed version is often called shimmy or wobble. It can be triggered by a bump while the front is light under acceleration, by a crest, or by worn parts.

Contributing causes include worn or loose steering head bearings, wrong tyre pressure, worn or damaged tyres, unbalanced wheels, a misaligned rear wheel, poorly set suspension and heavy luggage or a top box loaded high at the rear.

If it happens: keep a light grip, do not fight the bars, roll off the throttle smoothly and stay looking ahead. Afterwards, find the cause before riding fast again; a steering damper helps on sport and off-road bikes.