Handlebar flutter
Speed wobble ( engl. Shimmy or wobble ) is a phenomenon in two-wheeled vehicles .
A small amount of excitation leads to vibrations in the front fork when driving (on motorbikes usually between 60 and 80 km / h, on bicycles from 20 km / h) . These can reinforce themselves or build up in the area of the natural frequency of the system and then cause the handlebar to oscillate in a partial area of the steering stop . The vehicle continues to drive straight ahead and does not perform any significant rolling or stirring movements. The flutter does not have the power of the handlebars and cannot knock the handlebars out of the rider's hand; it does not normally lead to falls. Various causes are held responsible for the suggestion. A not evenly worn or unfavorably shaped front tire is discussed, an unfavorable load distribution (for example a bag on the luggage rack on a bicycle), a fork bearing that is set too tight or too loosely, and more. With racing bikes, handlebar flutter occurs relatively often, if the handlebars are then gripped out of shock, the effect can intensify. The well-known remedy on the racing bike: Put your elbows on your knees, so the body acts as a steering damper.
Origin of the name and (theoretical) mechanical background
This phenomenon, also known as the shimmy effect , was originally called nose or tail wheel flutter and at the beginning of the 20th century was mainly a problem for aviators, hence nose wheel flutter. Due to the higher take-off and landing speeds of the aircraft, especially the first jet-powered aircraft, it happened time and again that the nose wheels were set in vibration and thereby damaged and even broke. Theoretical research on this problem came at a time when a fashion dance called shimmy , in which the buttocks were vibrated, hence the name shimmy effect . Another name for this effect is known as tea cart wheel flutter , which can still be observed today in shopping carts if the construction is not clean . The theoretical investigations and calculations showed that the stability of rotating wheels depends on various parameters, the most important of which are below: caster, suspension stiffness, tire type and dimension, speed. This phenomenon also occurred in the automotive industry, among other things favored by wheel suspensions whose wheel carriers had a high moment of inertia : Dubonnet spring knees , MacPherson struts . The term shimmy effect was reanimated and known to a wider audience again in the seventies, when stability problems occurred on the front axle of some motorcycles, rocking or handlebar flutter. Aerodynamic causes also played a role here.