Safety assessment of personal mobility devices with different wheel size based on their dynamic stability performance

Abstract

There has been a rapidly growing trend in the use of small-wheeled personal mobility devices (PMDs) such as small-wheeled electric scooters and bicycles for urban mobility in many cities worldwide. However, it is a well-known fact that most of them do not ride as well as conventional big wheel bicycles, and the ride is often described as 'twitchy', 'wobbly' and 'less stable'. A considerable number of casualties involve single-vehicle accidents which can be correlated to their dynamic stability performance. This paper relates the vehicle frame design with safety performance. By using a well-defined mathematical model, the dynamic stability of different personal mobility devices was compared. The research confirms the lesser stability in existing small wheel electric scooters and bicycles. However, the investigation has also found that the reason is not so much the size of the wheel, but the inadequacy of current design practice to properly account for the complex influence of wheel size on stability. Finally, a case study has been presented to illustrate that current designs of small wheel PMDs can be improved for better stability and safety.