Science Fair Project Encyclopedia
Single speed bicycle
A single speed bicycle is a type of bicycle with a single gear ratio. Without derailleur gears or hub gearing, a single speed is mechanically simple. With fewer parts, they are durable and dependable, lighter than multi-gear bicycles, and easier to build yourself. The difference between a single speed and a fixed gear bicycles is the method of gear to wheel attachment. With a fixed gear bicycle, the rear gear is directly attached to the wheel, allowing the rider to pedal backwards to slow and stop the bike. A single speed has the rear gear attached to a freewheel, which lets the wheel spin without the pedals turning and allows the rider to coast. Both types of bicycles can be called "single speed," and are referred to as fixed and free, depending on the relation of the back gear to the rear wheel. Due to this difference, a single speed bicycle will have one or two brake levers and brakes, while a fixed gear bike may have one or none.
Both mountain bikes and road bikes can be made as or changed into a single speed. Mountain bike single speeds often have a relatively close ratio of front-to-back gear size, which allows them to scale hills and deal with obstacles better than their cousins, the single speed road bikes. Road bikes with a single speed often have a large front and small back gear, and are best used in flat cities, such as Boston.
Single speed bicycles and fixed gear bicycles are popular with bicycle messengers for their reliability and durability. Depending on the situation, a messenger may prefer a mountain bike based single speed, which can be an urban tank, able to roll over almost any obstacle, or a road bike based single speed, which is fast and light.
One appeal of single speeds is their simplicity. An ambitious rider can build a reliable, light single speed without much trouble. Refitting used bicycles as single speeds or using old bicycle frames and components is the cheapest way to build a good bike.
Specialized, KHS , Cannondale, and Bianchi produce single speed models of their standard mountain bike and racing bicycle frames, some for competitive racing. Additionally, BMX bicycles and most bicycles for children are single speed.
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