Chain tensioners are intended to maintain the bicycle chain with the ideal tension to prevent the sprocket from jumping and the chain from slipping out of place. With these two tensioners, placed on each side of the rear wheel, you will be able to keep your bike\'s chain in perfect condition while pedaling.Bicycles with gears or speeds that have a cassette or freewheel system do not need to use this type of chain tensioners because the derailleur itself does this function. However, fixie or fixed gear bikes do need a tension system to keep the chain in its optimal state.