polkupyörän

Polkupyörä, or bicycle, is a two-wheeled vehicle typically propelled by human power through pedals connected to a drivetrain. The main components are a frame, two wheels, a steering system (handlebar), a saddle, brakes, and a chain or belt drive that transmits pedaling force to the rear wheel. Modern bicycles vary in design for different uses, including road, mountain, city/commuting, and folding forms; many models are equipped with gears, and an increasing number are electric-assisted (e-bikes) with a motor helping pedaling.

History and design: The bicycle emerged in the 19th century from early velocipedes and draisines. The practical safety bicycle with equal-sized wheels and a chain drive developed in the 1880s, leading to the standard configuration used today. Materials evolved from iron to steel, then aluminum and carbon fiber; frame geometries and braking systems have advanced to improve efficiency, comfort, and safety. Common features include rim or disc brakes, pneumatic tires, and drivetrain components; innovations such as gearing systems and weather protection features (fenders) became widespread.

Use and context: Bicycles are used for transportation, sport, and recreation and provide a low-emission alternative to motorized transport. In Finland, cycling is a common part of everyday life, supported by cycling infrastructure and seasonal variations; many riders continue in winter with appropriate tires, lights, and clothing. Maintenance basics include regular lubrication of the chain, tire pressure checks, and periodic inspection of brakes and gears. Safety considerations involve obeying traffic rules, using lights and reflective gear in low visibility, and considering helmet use according to personal or regional recommendations.