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发表于 2006-11-22 17:23:58
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Bicycle Wheel
INTRODUCTION
When I tried to build my first wheels, I found no books on wheels, and magazine articles offered little help. There was no information about why I should use a particular hub, rim, spoke, or spoke pattern other than that one was "more responsive" than another. The little information I could find was vague and often contradictory.
Where I expected to find the technical principles of wheel building, I found lore and mystique but no written record of the wire-spoked wheel. I believe there was no record because, as a craft, wheel building had generally been learned through informal apprenticeship. It seemed that as long as wheels worked, they were considered unworthy of further investigation. Some builders who developed methods that produced better wheels made their techniques known, others apparently either kept them secret or failed to recognize their significance.
Guided by engineering principles, and with time and experience, I learned to build true and durable wheels. By observing failures, I discovered the effects of different building techniques and various components. Today I realize that the poor quality of the spokes available at that time helped my discoveries. These spokes quickly revealed the merits of different building techniques by a change in their rate of failure.
INTRODUCTION
Bicycles endure unusually high stresses at unusually low speeds, and for this reason seem to violate many design rules that apply to other machines. Because the bicycle is unusual, conventional wisdom has at times led to misconceptions about its wheels. I wrote this book to preserve the information that I gathered and to help others avoid errors that often have led to failures. I hope it fills the void that I perceived.
THE WHEEL: ANCIENT AND MODERN
Although the origin of the wheel may be obscure, its invention as a load carrying device marked the advent of machinery. Today the wheel is an essential part of most machines in the form of gears, pulleys, cams, sprockets, bearings, and other rotating devices. However, it is still most conspicuous as a load carrier; and, from a technical perspective, the bicycle wheel stands out as one of the most elegant of these.
The wire-spoked bicycle wheel was introduced more than a century ago to replace wooden wheels with thick, rigid spokes. Tensioning the wires made these wheels possible, and with them came the lightweight bicycle that we know today. Wire spokes not only reduced weight but also improved durability. Today's wire wheels can carry more than a hundred times their own weight. In off-road bicycling, skilled riders often jump from high obstacles, subjecting their wheels to forces of more than a quarter ton. The wheel's strength is even more impressively demonstrated in the heat of competition where these forces are encountered repeatedly at high speed. Although the bicycle is the world's most common vehicle, few people understand how its wheels achieve their unusual strength.
THE DISK WHEEL
Since earlier editions of this book, disk and other streamlined wheels have been allowed in bicycle racing. This may have been an unfortunate decision because their use has not improved enjoyment of the sport for either participant or spectator, and their construction is out of the hands of bicycle shops and users. Disk wheels are expensive, heavy, and wind sensitive. Although they have contributed toward slight increases in record speeds, they have substantially increased the cost of competing. Because the rule against "unfair advantage" specifically prohibits using any device that is not available to all racers in an event, these wheels give no competitive advantage. Unlike other technical advances, they have not made bicycles safer or simpler to operate.
The book is divided into three parts. Part I (theory) explains how wheels respond to loads. It investigates the merits of various designs and components, and the causes of their failures. Part II (practice) gives a step-by-step guide for building front and rear wheels as well as wheels with various patterns and numbers of spokes. Part III (data and equations) contains test results and equations for computing spoke lengths and other wheel dimensions. |
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