Three-speed bicycle
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The three-speed bicycle is a bicycle that uses internal hub gears at the rear wheel hub to provide three gear ratios. Typically, in low gear, the rear sprocket turns faster than the wheel; in middle gear, the rear sprocket turns at the same speed as the wheel; in high gear, the rear wheel turns faster than the sprocket.
Three-speed hubs have been in use since before the 1930s. Though they are heavier and less mechanically efficient than comparable derailleur systems, internal-gear hub systems are generally longer-lasting and require less maintenance, making them popular in many parts of the world for commuting and other types of utility cycling.
Internal-gear hubs come in a variety of models, including three-, five-, seven-, and even 14-speed versions. Notable manufacturers of internal-gear hubs include Sturmey-Archer, an early pioneer (now owned by SunRace); Rohloff; SACHS/SRAM; and Shimano.