Instability resulting from high center of gravity in motorcycles

Cursory glances at motorcycles on the roads would reveal that motorcycles with large engine capacity (e.g., 500 cc or 250 cc) are likely to be more unstable than ones of 125 cc engine capacity. Specifically, motorcycles of large engine capacity are typically larger at the upper portions of the motorcycles compared to ones with small engine capacity.


Motorcycles are by construction unstable, given their two wheel nature. Hence, emphasis is usually placed in designing a motorcycle with center of gravity as low as possible to afford a higher level of stability necessary to reduce the risk of falls on the roads. Specifically, motorcycles need to bank either to the left or right when they make a left or right turn respectively. In the case of a high center of gravity, a tight road bend would possibly cause the motorcyclist to lose control of the motorcycle as he may need to bank the bike significantly to the left or right. A high center of gravity would cause the motorcycle to have a large moment of inertia that could result in toppling and loss of control of the motorcycle.


On the other hand, a motorcycle with a low center of gravity would be easier to control, given its enhanced stability at bends, even ones with significant curvature. This comes about through a smaller moment of inertia generated when the motorcycle pivots slightly to the left or right during a turn, which is not sufficient to induce a fall of the motorcyclist; thereby, allowing the motorcycle to stay upright.


Hence, classical physics dictate that motorcycles need to have a low center of gravity to afford higher stability in corners, especially ones of high curvature. Specifically, a low center of gravity would generate a corresponding smaller moment of inertia when the motorcycle banks to the right or left in preparation for negotiating a bend, which helps reduce the risk of falls and toppling.


Category: mechanical engineering, physics,

Tags: moment of inertia, center of gravity, motorcycle,


Acknowledgement: Ng Wenfa thank Seah Kwi Shan for co-authoring this blog post.


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