All About Dropouts

Dropouts are the part of your bike frame where the wheel’s axle rests (See picture). Different dropouts let your bike do different things. There primary purpose is to keep your wheel in place and hold tension on your chain.

Standard Drop Out

The standard drop out is, most common. It is just a slot that allows the axle to rest. These almost always include a derailleur hanger for mounting a rear derailleur. Unlike the other styles of drop outs they don’t allow for chain tension adjustment. For standard drop outs a rear derailleur or other device acts as a chain tensioner in order to keep the chain from skipping over gears

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Horizontal Drop Out

Horizontal drop outs, also called track drop outs, are usually found on single speed specific bike frames. These allow for the wheel to be moved backward or forward in the drop out to get the perfect chain tension. A chain tensioner, also called a chain tug, fits inside of the drop out and setscrews adjust the tension. Sometimes these will include a derailleur hanger to mount a rear derailleur, but it is rare.

Front Facing Horizontal Drop Out

Front facing horizontal dropouts are angled and allow the chain tension to be adjusted a bit. These are common on older bikes to help get the tension perfect. They work well for single speed applications as well, and because of the angled design of the dropout, the tension will pull against the frame and the quick release. That means that a quick release can usually hold the tension on the chain without slipping, whereas a horizontal dropout usually requires a chain tensioner or bolt-on hub. With a normal horizontal drop out, the chain pulls directly against the quick release. These almost always include a hanger to mount a rear derailleur.

There are also all kinds of hybrid designs on the market: Everything from drop outs that morph from standard to horizontal, to strange eccentric drop out designs.