A Solution of the Low-Speed Wheel Flutter Instability in Motorcycles

Motorcycles are subject to two dynamic steering instabilities, a low-speed ‘flutter’ at 6–8 Hz. and a high-speed ‘weave’ at 2-3 Hz, both of which are increased by adding a tail load, or by decreasing the rider mass. This paper is concerned with the low-speed instability, and describes work which resulted in the elimination of this potentially dangerous phenomenon from a current large-capacity motorcycle. The cause was found to be twofold: a fundamental castor instability at the front wheel, coupled to a resonance in the upper section of the main frame. Recommendations on future frame design are made, and fundamental limitations of the ‘telescopic’ front fork are demonstrated.