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Michael Paine

Sydney, Australia

The previous discussion about bicycle wheel size is related to several road safety projects that I have undertaken on recreational scooters, children’s bicycles and mobility scooters, which have small wheels compared with road bikes.

A small wheel is less likely to be able to roll smoothly over a relatively small obstacle in the path. This is a simple geometric relationship – the contact force (which is effectively at right angles to the tyre surface) will have a larger horizontal component with a smaller wheel. This means that the vehicle will experience a larger deceleration than a vehicle with larger wheels and may even stop suddenly, which isn’t great for the rider.

The safety tests that I used for my projects included an obstacle test that demonstrated this relationship. The mobility scooter requirements, which are now part of a Standards Australia technical specification, include a raised obstacle test as well as a simulation of the gap at a railway level crossing, which has similar geometric challenges.

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