Speed wobble

Arm flapping (English shimmy or wobble ) is a phenomenon in two-wheelers.

A small excitation stimulates while driving ( on motorcycles usually between 60 and 80 km / h on bicycles already at 20 km / h) oscillations in the front fork to. These vibrations can reinforce itself or could build up in the system natural frequency and then cause the arm swings in a portion of the steering stop. The vehicle then travels straight ahead and does not carry significant body roll or stir- made ​​. Flapping does not have the force of the arm and hitting the driver can not beat out of hand the handlebars; it does not normally leads to falls. Various causes are responsible for the excitation. A non- uniform of worn or unfavorably shaped front tire is discussed, an unfavorable load distribution (eg bag on luggage rack on a bicycle ), a too tight or too loose adjusted fork bearings, etc.. When racing bikes handlebars Flapping occurs relatively frequently, the driver is then clasped from fright can intensify the effect. The well-known remedy on the bike: put elbows on his knees, the body acts as a steering damper.

Origin of the name and (theoretical ) mechanical background

This shimmy effect was originally named as a bug or Spornradflattern and made in the early 20th century, primarily the air riders a problem, therefore Bugradflattern. The higher take-off and landing speeds of aircraft, particularly the first emerging jets, it happened again and again that the nose wheels vibrated and were damaged thereby, and even broke. The theoretical investigations on this problem fell into a period in which a dance craze called " Shimmy " was current, in which the buttocks was caused to vibrate, hence the name " shimmy " effect. Another name of this effect is also known as " Teewagenrad Flutter ", which even today can be seen in the shopping cart if the design is not " clean". The theoretical investigations and calculations showed that the stability of rotating wheels depends on various parameters, below the most essential: caster, suspension stiffness, tire and dimension, speed. In the automotive industry this phenomenon occurred as well, among other things, facilitated by the advent of lightweight construction. Example: MacPherson front axle, caravan trailer. Known " reanimated " and more widely the term shimmy effect was back in the seventies, when encountered stability problems on some motorcycles at the front, " swaying " or arm flapping. The fact that here also starred aerodynamic reasons, it should be noted in passing.