Investigating Novel Bicycle Braking Systems for Preventing Over-The-Handlebar Flips

Abstract

Objectives: Over-the-handlebar pitch-over is an unforgiving failure mode in bicycle braking, whereas automobile anti-lock brakes are designed to avoid wheel locking. This review discusses why the two-wheeled and four-wheeled vehicles’ dynamics differ so dramatically for such a similar maneuver. It also evaluates the effectiveness of two concepts of bicycle braking systems that can prevent pitch-over: brake biasing and brake cable length extension.

Methods: The pitch-over threshold was established by equating the moment around the front contact patch due to the center of mass with the moment caused by the friction force at the rear wheel contact patch. It was then compared to the tire’s adhesion limit to define the critical value at which the bicycle will either lock its wheels or pitch-over. Finally, the two considerations were analyzed using seven criteria: modulation, performance, safety, cost, mechanical/electrical complexity, and bicycle categories.

Results: A bicycle’s pitch-over threshold depends solely on geometry, specifically the ratio between the horizontal distance from the front contact patch to the center of mass location and the center of mass height. For a typical bicycle, it means that the critical value is lower than the adhesion limit on dry pavement. In other words, a bicycle will always pitch-over before any of its wheels lock during the emergency stop. Brake biasing redistributes braking effort from front to rear wheels and is a logical choice for higher-end bicycles, such as e-bikes and mountain models, because it uses existing electronics in the braking system. Its performance is limited by the same physics that make bicycles dangerous, namely, the front wheel’s normal force variation, which disappears entirely at the pitch-over threshold. Meanwhile, the brake cable length extension concept addresses the fundamental problem of compliance by allowing a longer throw before the maximum braking power is reached. It is a mechanically simple and cheap solution, which makes it ideal for lower- and mid-range bicycles, but it may sacrifice modulation and performance in a situation when the shortest possible stopping distance is necessary.