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 The Wheel Page: 2 of 3


The Safety Bicycle

The safety bicycle that was developed in the 1880s closely resembles the bicycles 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.

Stills from Edison Movie
Click on the image to view a QuickTime clip (3.1 megabytes).
LIBRARY OF CONGRESS
The image shows stills of a saftey bicycle and rider from an 1899 Thomas Edison film.

 Spokes

Even the earliest bicycles 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 bicycle 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 bicycle 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 tire of your bicycle rotates while it moves forward along with you and the bike.

 

 The Bicycle Craze of the Late 1800s

In the America of 1867 most people got around by on horse or on foot. That was the year that the first factory-produced bicycles arrived on American shores from Europe. Though the first high-wheeled "Ordinaries" were quite expensive, costing about $100-150 (at a time when median annual incomes hovered around $450), they were destined to become the rage. The appeal of speed was strong, and bicycles offered mobility to young people and to women, an unprecedented revolution in social freedom.

The craze caught fire with the production in 1887 of the Victor Bicycle, a machine with two identically sized wheels and a chain drive much like a modern bicycle. By 1885, over 400 bicycle factories were working non-stop to keep up with skyrocketing demand. In 1895, Americans bought 2 million bikes, one for every 27 people in the country. Cycling "academies," clubs, and professional races sprang up across the land.

But in 1902, Henry Ford introduced his "Tin Lizzy" automobile, and the bicycle craze was quickly replaced with an obsession with the car. The 1960s saw the beginning of a resurgence for the bicycle, and in 1984 Americans bought 14 million bikes, compared with 10 million cars.



Tangential & Radial Spokes

There are many different ways to spoke a bicycle wheel. Most bicycles have tangential spokes, meaning that the spokes do not connect from the hub to the rim in a straight line, but at an angle. There are many different patterns of tangential spokes. Occasionally bicycles will have completely radial spokes. These spokes go straight from the hub to the rim of the tire. Wheels typically have tangential spokes. The way in which the wheels are spoked determines how they will perform.


WheelImage
A bicycle wheel with tangential spoking.
 "You can spoke the front wheel completely radially, but the rear wheel had better not be spoked radially. There is no way to convey the twist of the wheel out to the rim to drive you forward," Exploratorium Senior Scientist Paul Doherty explained. Tangential spoking helps transmit the torque from the hub out to the tires.

Not only would a radially spoked rear wheel be less efficient than one spoked tangentially--it would be significantly weaker. A bicycle wheel needs to be able to handle a variety of forces. Besides holding up the weight of the cyclist, a wheel must withstand the forces of pedaling and braking and the jarring effects of the road surface. The benefit of radial spoking has to do with the stiffness of the wheel (less deformation makes the wheel slightly more efficient).

Paul Doherty
RealMedia Clip
The Exploratorium's Paul Doherty talks about different spoking patterns.
 

 The Wheel Page: 2 of 3
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