A bicycle is a two-wheeled human-powered vehicle. The wheels are one behind the other. Most bicycles are propelled by pedals driven by the rider's feet. A frame connects the wheels, allows the front wheel to be turned from side to side for steering, provides a seat for the rider, and holds the shaft on which the pedals turn. Bicycles serve as a popular means of transportation in many nations, and as a form of recreation virtually world-wide. A bicycle is also known as a cycle, a bike, or a pedal cycle (this last is to distinguish it from a motorcycle).
The first recorded "two-wheeler" was the "draisine" designed in 18th century Germany by Baron Karl von Drais, possibly for use in traveling his estate to collect rents from his tenants. Decades later, Scottish blacksmith Kirkpatrick MacMillan added a pedal and chain drive mechanism to create the most credible prototype of the modern bicycle. Subsequent improvements included Englishman J.K. Starley's now-familiar diamond-shaped frame, Dunlop's pneumatic tire, multiple-gear options, and increasingly sophisticated brakes. The basic design of bicycles was relatively unchanged through the first half of the 20th century, but many subtypes of bicycles have subsequently evolved, including the racing bike, road bike and mountain bike, to suit the needs of specific cyclists.
A bicycle can be a very energy-efficient means of transport. A well-maintained chain-driven bicycle can achieve efficiencies of over 98%, though the use of gearing mechanisms may reduce this to as low as 80% in some gears, with hub gears being generally a little less efficient than derailleur gears. Bicycle tires can also affect efficiency. Tires with little or no tread and pumped up hard are much more efficient than (mountain-bike style) knobbly tires which are not usually pumped up hard (but the latter may result in a more comfortable ride).
A folding bicycle has one or more hinges incorporated in the frame so that the bike can be folded into a smaller package, either for storage or to allow of it being carried on public transport. Folding bicycles often have relatively small wheels which allow a smaller folded package and which may result in a different 'feel' when being ridden.
An electric bicycle uses an electric motor powered by a rechargeable battery to reduce pedalling effort. The motor is often mounted in the hub of a wheel. In many jurisdictions, the maximum motor power and/or the maximum powered speed may be limited in order for the vehicle to continue to qualify as a bicycle (no driving licence or insurance required).