Classic MotorcyclesGet more information and check out pictures of vintage motorcycles in our Classic Motorcycles section.

­ Sinc­e 1998, the number of motorcycles in the United States has increased by 34 percent [ref]. Why the sudden spike in popularity? Unlike cars, motorcycles allow riders to connect intimately with the driving experience. But it's not just about adventure and freedom. With gas prices soaring, motorcycles, which can achieve fuel economies as high as 85 miles per gallon, provide an attractive alternative to gas-guzzling cars.

In this article, we'll learn how the modern motorcycle operates, how motorcycle design has evolved over the years and how motorcycles might change in the near future.

Motorcycle Image Gallery

Photo courtesy Dee Kull, MorgueFile See more motorcycle pictures.

­ ­Motorcycle Basics
Motorcycles are motorized vehicles for transporting one or two riders. Generally, a motorcycle has only two wheels, but any vehicle with fewer than four wheels in contact with the ground can be classified as a motorcycle. Three-wheel variations of the motorcycle include the "hack" (motorcycle plus sidecar) and the "trike" (short for motortricycle).

Photo courtesy Kenn Kiser, Pixel Perfect Digital 2001 Honda Gold Wing GL 1800 with Monarch trike conversion

The layout of the modern motorcycle was established by 1914 and has remained fundamentally unchanged ever since. The overall structure and function of a motorcycle is quite simple. It includes a gasoline engine, which converts the reciprocating motion of pistons into rotary motion, just like the engine in a car. A transmission system transmits this motion to the back wheel. As the back wheel turns, it propels the motorcycle forward. Steering is accomplished by turning the front wheel via the handlebars and by leaning the bike to one side or the other. Two hand levers enable the rider to operate the clutch and the front brake, while two foot pedals enable him to change gears and control the rear brake.

Next, we'll take a close look at a motorcycle engine.

­Motorcycles Go To War A Harley-Davidson military motorcycle When World War I started in 1914, the automobile did not own the roads. Motorcycles filled the gaps as dependable, reliable vehicles. In the war, their utilitarian nature was put to good use. American and European armies used motorcycles extensively to gather reconnaissance, deliver messages and, in some cases, engage in combat. In 1917, roughly one-third of all Harley-Davidson motorcycles produced were sold to the U.S. military; in 1918, that figure rose to 50 percent. By the end of the war, it is estimated that the Army used some 20,000 motorcycles -- most of them Harley-Davidsons [ref]