A “Crash” Course on Motorcycles & Motorcycle Expertise


By Curtis M. Beloy, P.E. ::::

Motorcycles are unique vehicles that require special training and licensing to operate. They have unique handling characteristics and respond to disturbances differently than passenger vehicles. From a very simplistic point of view, a motorcycle can be thought of as being comprised of two wheels, a front structure that includes the handlebars and front fork, and a rear structure that includes the frame, fuel tank, and motor. The motorcycle contacts the ground at two points- the contact patches of the front and rear wheels. Unlike passenger vehicles, motorcycles are subject to unique vibrations and instability due to their ability to pivot about the joints on the motorcycle and the contact patches with the road. Because of this design, motorcycles can “weave” and “wobble” while traveling down the road, as well as lean/tip over (capsize) to the side.

The gyroscopic effect of the wheels is a very important part the dynamic behavior of motorcycles. For one, the gyroscopic effects of the wheels stabilize the motorcycle, making it easier to maintain in an upright position at operating speeds. The gyroscopic effect of the front wheel is also very important in how the motorcycle is steered. A force that turns the front wheel, such as an input to the handlebars, will result in the motorcycle leaning to the side based upon the law of physics known as conservation of angular momentum. That is, motorcycles steer by leaning, and the lean is initiated through a reaction to the gyroscopic effect of the front wheel as opposed to shifting a rider’s weight to the side of the motorcycle. The motorcycle will then take on a new behavior while leaned and cornering, including the suspension and response to bumps and its braking and acceleration characteristics.

Understanding how a collision occurred is largely dependent on the ability of an expert to interpret physical evidence in order to understand how the vehicle moved over the road surface during certain points in the collision sequence. As such, specific knowledge of motorcycle dynamics is very helpful in interpreting physical evidence in a motorcycle-related incident. It is also necessary to understand how that movement is related to the force from a collision, an operator reaction, or a disturbance in the roadway.

An example of this would be the evaluation of a single-vehicle incident in which a roadway irregularity is alleged as a causal factor. A non-motorcycle-specific reconstruction expert might be able to tell you what side the motorcycle fell to, how far it slid, and an approximation of the travel speed of the motorcycle when it fell to the ground. However, a reconstruction expert knowledgeable in the field of motorcycle dynamics would be able to report how the motorcycle got from its wheels to its side and whether or not it makes sense that the interaction with the roadway feature would initiate that type of movement. Understanding the dynamic responses of motorcycles is critical in this type of issue.

An advanced understanding of motorcycle dynamics will also assist in evaluating the reactions of a motorcycle operator. Some questions might be whether the motorcyclist braked with one brake, two brakes, or attempted to brake and steer when responding to a perceived hazard. Behavior of motorcycles under aggressive braking is dependent on the geometry of the motorcycle, the type of road surface, and even the type of braking system on the motorcycle itself.

In addition, if a motorcycle expert has significant competitive experience on motorcycles, it is also likely that he or she will have first-hand familiarity with loss of control events that are an inevitable part of competitive motorcycle racing. This experience is invaluable in understanding motorcycle dynamics and is sometimes only gained along with a trip to the emergency room. Most casual motorcycle operators will not experience the limits of motorcycle handling and the consequences of exceeding those limits.

In any motorcycle accident case, questions eventually arise regarding the motorcyclist’s actions and whether those actions were reasonable. Each situation needs to be evaluated individually in order to understand the factors that would go into the motorcyclist’s decision of where to travel or how to react. Additionally, a motorcycle expert should be able to identify the signs of mechanical issues with the motorcycle, the effects on the stability of the motorcycle, how that mechanical issue may have been detected, and whether it is a result of poor maintenance or design.

Curtis M. Beloy, P.E. is a Collision Reconstruction Engineer at DJS Associates, Inc. specializing in the evaluation of motorcycle- related incidents. He can be reached at experts@forensicDJS.com or at (215) 659-2010.

(Originally published in January 2013 issue of New Jersey Association for Justice – page 2)

Categories: Case Studies


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