Cycling, also called bicycling or biking, is the use of bicycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as “cyclists”, “bikers”, or less commonly, as “bicyclists”. Apart from two-wheeled bicycles, “cycling” also includes the riding of unicycles, tricycles, quadracycles, recumbent and similar human-powered vehicles (HPVs). Bicycles were introduced in the 19th century and now number approximately one billion worldwide. They are the principal means of transportation in many parts of the world. Cycling is widely regarded as a very effective and efficient mode of transportation optimal for short to moderate distances. Bicycles provide numerous benefits in comparison with motor vehicles, including the sustained physical exercise involved in cycling, easier parking, increased maneuverability, and access to roads, bike paths and rural trails. Cycling also offers a reduced consumption of fossil fuels, less air or noise pollution, and much reduced traffic congestion. These lead to less financial cost to the user as well as to society at large (negligible damage to roads, less road area required). By fitting bicycle racks on the front of buses, transit agencies can significantly increase the areas they can serve. Among the disadvantages of cycling are the requirement of bicycles (excepting tricycles or quadracycles) to be balanced by the rider in order to remain upright, the reduced protection in crashes in comparison to motor vehicles, often longer travel time (except in densely populated areas), vulnerability to weather conditions, difficulty in transporting passengers, and the fact that a basic level of fitness is required for cycling moderate to long distances.
Cycling quickly became an activity after bicycles were introduced in the 19th century. Today, over 50 percent of the human population knows how to ride a bike.
In many countries, the most commonly used vehicle for road transport is a utility bicycle. These have frames with relaxed geometry, protecting the rider from shocks of the road and easing steering at low speeds. Utility bicycles tend to be equipped with accessories such as mudguards, pannier racks and lights, which extends their usefulness on a daily basis. As the bicycle is so effective as a means of transportation various companies have developed methods of carrying anything from the weekly shop to children on bicycles. Certain countries rely heavily on bicycles and their culture has developed around the bicycle as a primary form of transport. In Europe, Denmark and the Netherlands have the most bicycles per capita and most often use bicycles for everyday transport. Road bikes tend to have a more upright shape and a shorter wheelbase, which make the bike more mobile but harder to ride slowly. The design, coupled with low or dropped handlebars, requires the rider to bend forward more, making use of stronger muscles (particularly the gluteus maximus) and reducing air resistance at high speed. The price of a new bicycle can range from US$50 to more than US$20,000 (the highest priced bike in the world is the custom Madone by Damien Hirst, sold at $500,000 USD ), depending on quality, type and weight (the most exotic road bicycles can weigh as little as 3.2 kg (7 lb) ). However, UCI regulations stipulate a legal race bike cannot weigh less than 6.8 kg (14.99 lbs). Being measured for a bike and taking it for a test ride are recommended before buying. The drivetrain components of the bike should also be considered. A middle grade dérailleur is sufficient for a beginner, although many utility bikes are equipped with hub gears. If the rider plans a significant amount of hillclimbing a triple-chainrings crankset gear system may be preferred. Otherwise, the relatively lighter and less expensive double chainring may be better. Much simpler fixed wheel bikes are also available. Many road bikes, along with mountain bikes, include clipless pedals to which special shoes attach, via a cleat, enabling the rider to pull on the pedals as well as push. Other possible accessories for the bicycle include front and rear lights, bells or horns, child carrying seats, cycling computers with GPS, locks, bar tape, fenders (mud-guards), baggage racks, baggage carriers and pannier bags, water bottles and bottle cages. For basic maintenance and repairs cyclists can carry a pump (or a CO 2 cartridge), a puncture repair kit, a spare inner tube, and tire levers and a set of allen keys. Cycling can be more efficient and comfortable with special shoes, gloves, and shorts. In wet weather, riding can be more tolerable with waterproof clothes, such as cape, jacket, trousers (pants) and overshoes and high-visibility clothing is advisable to reduce the risk from motor vehicle users. Items legally required in some jurisdictions, or voluntarily adopted for safety reasons, include bicycle helmets, generator or battery operated lights, reflectors, and audible signalling devices such as a bellor horn. Extras include studded tires and a bicycle computer. Bikes can also be heavily customized, with different seat designs and handle bars, for example.