motorcycle

Introduction

any two-wheeled or, less commonly, three-wheeled motor vehicle, usually propelled by an internal-combustion engine.

 

History

Just as the automobile was the answer to the 19th-century dream of self-propelling the horse-drawn carriage, the invention of the motorcycle created the self-propelled bicycle. The first commercial design was a three-wheeler built by Edward Butler in Great Britain in 1884. It employed a horizontal single-cylinder gasoline engine mounted between two steerable front wheels and connected by a drive chain to the rear wheel.

By 1900 many manufacturers were converting bicycles, or pedal cycles as they were sometimes called, by adding small, centrally mounted spark ignition engines. The need for reliable constructions led to road trial tests and competition between manufacturers. The original Tourist Trophy (TT) races were held on the Isle of Man in 1907 as reliability or endurance races. Such events have been the proving ground for many new ideas from early two-stroke-cycle designs to supercharged, multivalve engines mounted on aerodynamic, carbon-fibre reinforced bodywork.

 

Components

Motorcycles are produced with both two-stroke- and four-stroke-cycle engines and with up to four cylinders. Most are air-cooled, though a few are water-cooled. Engines are generally limited to 1,200-cubic-centimetre (73-cubic-inch) displacements. The smallest designs, termedmopeds(frommotorpedal), have very small (50 cubic centimetres) engines offering 100-miles-per-gallon fuel economy. Such units are not permitted on limited-access public roads because of their low speed capability. In order of increasing power capacity and engine displacements are the other four classifications of motorcycles: trail bikes, road bikes, touring bikes, and racing bikes. The highest performance levels in racing are attained by “superbikes” with up to 160 horsepower produced for vehicles weighing approximately 500 pounds.

The motorcycle frame is often of steel, usually a combination of tubes and sheets. The wheels are generally aluminum or steel rims with spokes, although some cast wheels are used. Graphite and magnesium parts are increasingly in use because of high strength-to-weight characteristics. Tires are similar to those used on automobiles but are smaller and rounded to permit leaning to lower the centre of gravity in a turn without losing traction. Front-wheel suspension is provided by coil springs on a telescopic fork; rear-wheel springs are often mounted on shock absorbers similar to those used in automobiles.

Transmissions on motorcycles typically have four to six speeds, although small bikes may have as few as two. Power is normally transmitted to the rear-wheel sprockets by a chain, though occasionally belts or shafts are used.

The clutch and throttle, which controls engine speed, are operated by twist-type controls on the handgrips. The front-wheel brake is controlled by a lever near the hand grip; the rear-wheel brake is engaged by a foot pedal. Except on very small machines, the front brake is usually of the hydraulic disc type. The rear brake may be disc or drum. The kick starter has been mostly replaced by an electric push-button starter.

 

George C. Cromer

Additional Reading

The terminology of motorcycle technology is given in the concise SAE publicationA Dictionary of Terms for the Dynamics and Handling of Single Track Vehicles: Motorcycles, Mopeds, and Bicycles(1985).Eric ThompsonandLaurie Caddell,From Motorcycle to Superbike: The History of the Motorbike, 2 vol. in 1 (1986), is well illustrated.Erik H. Arctander,The New Book of Motorcycles(1968), describes various types of the vehicle.

George C. Cromer

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