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Understanding the Physics of Bicycles

Bicycling Science
By David Gordon Wilson with contributions by Jim Papadopoulos.

Excerpt from a review from Bicycle Quarterly
Vol. 3, No. 2 (Winter 2004):

Bicycles have been the subject of many scientific and pseudo-scientific studies over time, but the underlying physics are not always understood by those designing bikes, nor by those writing about them. Bicycling Science , in its third edition, attempts to explain why bicycles work the way they do, and how to optimize them. Chapters deal with human power, power and speed, aerodynamics, rolling resistance, braking, steering and balancing, power transmission, and materials. If you want to find the answers to common questions, for example, which brake provides the most braking power, you will find not only a simple explanation, but also the equations to prove it. (It is the front brake, as the rear brake barely touches the ground during an emergency stop.) Despite its thoroughness, the book is well-written and easy to read even for non-scientists. Numerous illustrations help with understanding and even provide entertainment. Gems include a human-powered submarine and a two-rider side-by-side unicycle with a huge wheel between the riders.

While some of the contents may be general knowledge among experienced cyclists, everybody will find interesting information in the pages of Bicycling Science . If you like to ride two abreast to chat, you will be glad to know that moving two vertical cylinders side-by-side at a distance of one diameter reduces the drag of each cylinder by 15%.

The author also explains why there is an unsafe speed for long braking with rim brakes on downhills: Going slow, there is enough time to dissipate the heat generated by braking, and going fast, less braking (and hence less heat) is required because more energy is dissipated by wind resistance. The speed at which most "cautious" cyclists tend to keep their bikes, 20-30 mph, is worst in that the descent occurs fast enough to generate significant energy due to the loss of elevation, but not fast enough to rely on wind resistance to dissipate much of that energy. So the rims get hotter than they would either at faster or slower speeds.

Interesting sidelines in the book include a way to calculate the optimum number of gears for a given rider, and a proposal for a human-powered vehicle on rails that should be able to reach speeds unattainable on the road.

I thoroughly recommend Bicycling Science especially to technically interested cyclists. It is well-written, easy to comprehend, and full of interesting and entertaining information.

Publisher: MIT Press
Year: 2004, 3rd Edition
Binding: Softcover
Pages: 485 pages, 266 illustrations
Dimensions: 6" x 9"

Price: $28