The Right Way to Ride the Wrong Bike: An Exploration of Klein's 'Unridable' Bicycle

Abstract

Professor Richard Klein and his students built a bicycle with a rather interesting feature: no one was able to ride it. A prize was offered. Hundreds of students and cycling enthusiasts attempted it. Years passed, and the prize money grew. This article is an exploration of the dynamics and control of the unridable bicycle from the perspective of an engineer determined to ride it. By developing simple models of a bicycle as an inverted pendulum attached to a wheeled carriage that provides steer kinematics, one can pinpoint a physical mechanism which explains why the rear-steered configuration is difficult to balance. By applying a state space control perspective, one can illuminate limitations and opportunities for stabilization. The end result is that Klein’s unridable bicycle is ridable, with the right strategy and ample practice.