Chainstopping

Chainstopping is a technique used in certain mechanical systems, most notably in bicycles, to prevent a chain from becoming excessively slack or to control its movement. The primary goal of chainstopping is to maintain a desired level of chain tension. This is often achieved through the use of a chain tensioner. These devices can be integrated into the drivetrain or be an add-on component.

In the context of single-speed bicycles or bicycles with internal gear hubs, where there is no rear derailleur to automatically adjust chain tension, chainstopping is crucial. Without it, the chain can sag, leading to it falling off the sprockets. This can disrupt the ride and potentially cause damage. Common methods of chainstopping include using a spring-loaded arm that pushes against the chain, effectively taking up slack, or employing eccentric bottom brackets which allow for minor fore-aft adjustment of the crankset to alter chain length.

Some modern bicycle drivetrains, particularly those designed for off-road use, incorporate advanced chain retention devices that go beyond simple tensioning. These can include specialized chainrings with taller, narrower teeth (narrow-wide profiles) and upper or lower guide mechanisms that physically prevent the chain from bouncing off. The effectiveness of chainstopping directly impacts the reliability and performance of the bicycle's drivetrain.