The wheel is the most crucial element of the cycle: it allows the rider to roll over the ground with great speed and efficiency. Historians believe the wheel originated in Mesopotamia sometime around 3,500 BC. While the Sumerians did not pedal their way through ancient Mesopotamia, animal-powered wheeled chariots and carts helped haul goods and people for thousands of years. During the industrial revolution in the 19th century, advances in materials and engineering made it possible to use the wheel effectively in human-powered machines. The modern cycle, complete with a steel frame, a chain drive, steel wheels and spokes, and pneumatic tyres, would emerge in the late 1800s.
On the Road
While the use of the wheel was widespread in ancient times, it did have limitations. The resistance to the motion of a wheel can vary tremendously depending on the surface on which it is traveling. A rough road is much harder to roll over than a smooth one. The Romans were aware of this and developed a massive network of paved roads. While this may have been the first time in history that roads were improved to facilitate the wheel, it certainly wasn't the last. In the United States in the 1890s, cyclists successfully lobbied for improvements in roads nationwide, and with cycling the nation's most popular sport at the time, legislators listened.
The Ordinary
When most people think about early cycles, the high-wheelers of the late 1800s come to mind. These early models had names such as the "Ordinary" or "Xtraordinary." In England, these cycles were also known as "penny farthings" because the large and small wheels were reminiscent of the large one-penny coin and the smaller farthing coin.
The pedals were attached directly to the front wheel of the high-wheelers. The larger the front wheel on an "Ordinary," the farther the cyclist would travel with each turn of the pedals. Exploratorium Senior Scientist Paul Doherty explained, "Every time the pedals would go around once, that whole giant front wheel would go around once. So, for one cycle of the bicyclist's legs he might go 140 inches (3.556 meters), a tremendous distance forward." This made pedaling up hills quite difficult, but allowed for great speed on the flats.
While the high-wheels were quite efficient, they were also dangerous: the cyclist was very high off the ground and perched precariously over the front wheel. So, while the high- wheelers broke new speed and distance records, they quickly gained notoriety for the dangers involved in riding them. The slightest obstacle in the road could result in a nasty head-first fall. "Headers" or "taking a header" were common terms used to describe an all-too-frequent problem. With a high center of gravity and narrow tyres made of solid rubber (which occasionally could roll off their rims), high-wheeled cycles were designed for speed, not for safety.
The Safety cycle
The safety cycle that was developed in the 1880s closely resembles the cycles of today. The rider is suspended on a metal frame between two wheels of equal size. A chain drive mechanism connects the pedals to the rear wheel. The stability and comfort of the design was superior to the high-wheelers, and so earned the "safety" its name.
Spokes
Even the earliest cycles used spokes of one sort or another. In fact, even in ancient times many chariots and animal-drawn carts used spokes. A spoked wheel can be made as strong as a solid one and have only a fraction of the weight.While early spoked wheels were almost always made out of wood, the cycle wheels and spokes of today are made out steel or aluminum or occasionally more exotic materials such as carbon composite or ceramics.
Minimizing the weight of the wheels is extremely important in cycle design. Why does weight matter? Each time you push the pedals, you have to accelerate the weight of the wheel both forward and around its center. In other words, the wheel undergoes angular and straight motion simultaneously. You can see this when you ride--the front tyre of your cycle rotates while it moves forward along with you and the bike.
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