1. 1904
   1914
2. 1934

The layout of the modern motorcycle has remained relatively unchanged since it was established in 1914.

1. the engine
   the front wheel
2. the rear wheel

Rotational force created by the crankshaft is transmitted to the motorcycle's rear wheel via the transmission.

1. the number of cylinders
   the number of strokes in its power cycle
2. the size of the camshaft

Motorcycle engines are generally classified by the number of cylinders they have, the capacity of their combustion chambers or the number of strokes in their power cycles.

1. Hell's Angels
   the U.S. military
2. the Salvation Army

During World War I, American and European armies used motorcycles extensively. In 1917, the U.S. military bought nearly one-third of all Harley-Davidson motorcycles produced; in 1918, that figure rose to 50 percent.

1. chain
   belt
2. waterjet

A chain, belt or shaft is used to transmit engine power to a motorcycle's rear wheel.

1. gear shaking
   shaft jacking
2. clutch clunking

Heavy shaft drives sometimes cause unwanted motion, called shaft jacking, in the motorcycle's rear.

1. body
   channel
2. chassis

A motorcycle chassis includes the frame, suspension, wheels and brakes.

1. cast wheels
   pneumatic tires
2. steel rims

Cast wheels allow the bikes to use tubeless tires, which, unlike traditional pneumatic tires, don't have an inner tube to hold the compressed air. Instead, the air is held between the rim and the tire, relying on a seal to maintain the internal air pressure.

1. hand levers
   foot pedals
2. both hand levers and foot pedals

Riders engage the front brake with a hand lever on the right grip and the rear brake with the right foot pedal.

1. "naked bikes"
   off-road bikes
2. sport bikes

Since they don't come standard with lights, mirrors, horns or mufflers, off-road bikes aren't street-legal.