Dynamics of pitch-over crashes

Going ‘over the handlebars’ is a common type of crash for cyclists. The high center of gravity and short wheelbase makes bicycles susceptible to this type of pitch-over if the rate deceleration is too high. Common causes are braking too hard with the front brake, hitting an obstacle or something getting stuck in the front wheel. This study observed all each of these types of events under controlled conditions in order to better understand the dynamics. A trained stunt person was instructed to ride a bicycle at approximately 20 kph (12.5 mph) towards a pitch-over initiation area. He would then either brake hard, ride into a fixed obstacle or trigger a dowel pin to be fired through the front wheel. The resulting pitch-over crash was filmed using high-speed photography.

.Targets placed on the cyclist and test track allowed the motion of the cyclist to be tracked and analyzed. It was found that crashes resulted in the cyclist landing on his head with a position which loaded the cervical spine. This is dangerous crash configuration. Previous research has shown that 6 percent of all bicycle accidents are caused by something being caught in the spokes. Preventing this cause as well as improving the longitudinal stability of the bicycles are therefore important safety factors.

Abstract:

In a controlled environment, bicycle crash tests were performed to analyze the dynamics of bicycle pitch-over, and the effect different test conditions would have on the motion of the bicyclist and the potential for serious head and neck injuries. The tests being evaluated within this paper will focus on a single size rider and bicycle with speed controlled between 19.3 and 22.5 kph (12.0 and 14.0 mph). The variables of the test conditions were the method of pitch-over initiation and configuration of the bicycle. Pitch-over was initiated by applying the front brake, impacting a rigid barrier, and inserting a dowel into the spokes of the front wheel. The bicycle configuration was varied by changing the frame, front fork, front wheel and stem. For all testing performed the event was captured on high speed video. As the testing progressed a force plate was added to measure the vertical loads and an impact plate was added to the barrier impacts to measure the horizontal impact loads. The data acquired from this series of tests provides insight into the dynamics of bicycle pitch-over, injury mechanisms, and the effect of bicycle component failure.

Reference:

Analysis of bicycle pitch-over in a controlled environment
Bretting, Gerald P. (Collision and Injury Dynamics Inc, United States); Jansen, Henricus P.; Callahan, Michael; Bogler, John; Prunckle, John Source: SAE International Journal of Passenger Cars – Mechanical Systems, v 3, n 1, p 57-71, August 2010

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