Chain Tensioning
Single-speed bicycle builders have devised a variety of methods for producing and maintaining the proper chain tension. The most common method is horizontal rear dropouts or track ends. These allow the rear wheel to be moved fore or aft as necessary. Using chain tugs with track ends ensures that optimum chain tension can be achieved with the wheel remaining centered. Another method uses an eccentric mechanism either in the bottom bracket or in the rear hub. If neither of these are an option, when working with an existing frame not originally designed for single-speed use for example, some kind of idler pulley, such as the Surly Singleator or simply a short cage rear derailleur can be used to take up chain slack. As well, finetuning the combination of chainring, cog, and chain length may suffice until the chain develops significant wear.
Throughout the years bicycle designers have produced belt-driven bicycles. While these belts cannot be shifted between gears like a chain, they offer singlespeed or hub geared drivetrains with improved increased wear resistance, quieter operation, and lubrication-free cleanliness. Belts also do not change length during their lifespan in the same way that chains "stretch" or increase in pitch as their link pivots wear. This keeps the pitch of the belt's teeth constant and dramatically decreases wear on gear teeth. Belts have failed to overtake chains in popularity for bicycles because they have historically been less efficient. Also replacement of the one-piece belt requires traditional diamond bicycle frames to have a special split chainstay.
Read more about this topic: Single-speed Bicycle
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