In this guide, we'll explain what a derailleur hanger is, what it does, and the different types available.

What is a derailleur hanger?

The derailleur hanger (commonly called a mech hanger) bolts onto the dropout and is responsible for connecting the rear derailleur to the frame.

Before derailleur hangers were widely used, the rear derailleur was bolted directly to the frame's dropout. While this was generally not a problem in the steel frame era, when aluminium and carbon fibre came into play, there was a greater chance of it snapping or bending.

While it is still advisable to fit a separate hanger to steel frames, it does make repairs easier.

What does a derailleur hanger do?

Derailleur hangers are sacrificial parts designed to bend or break on impact, protecting your rear derailleur and frame.

Accidents happen, and it's far cheaper to replace a derailleur hanger than a frame or rear derailleur.

It's crucial that your derailleur hanger is perfectly aligned for optimal gear shifting.

If the derailleur hanger is out of alignment, the gears won't shift correctly as the derailleur pulleys won't be correctly aligned with the cassette cogs. If it's bent far enough inwards, the derailleur can shift the chain into the spokes, damaging the derailleur and wheel.

While a heavy impact on the derailleur can bend the hanger, it can also happen in relatively innocuous situations.

Any damage to the drive side of your bike means the hanger could have taken an impact. It's worth checking the derailleur hanger alignment before trying to adjust your gears.

It's also a good idea to check the alignment on a new bike, as it's surprisingly common for them to be bent straight out of the box. Any good bike shop will incorporate this into their pre-delivery inspection (PDI).

Why are there so many different derailleur hangers?

For many years, derailleur hangers have been made for a specific frame. This is still the prevailing situation unless you have a performance mountain bike or some gravel bikes that use the SRAM UDH (which we went into more detail about last time).

Derailleur hangers come in a variety of shapes and sizes, and you must use the correct hanger for your frame.

Differences include whether it bolts to the inside or outside of the dropout, the number of bolts or types of bolts the hanger uses. In addition to this, the hangers often have other unique features.

Derailleur hangers are almost always model-specific, and it's common for manufacturers to change the hanger design partway through a model's run.

If a hanger breaks on a ride and you don't have a spare, you'll almost certainly end your ride. If the chain doesn't get tangled up, you can remove it from the rear derailleur, shorten it, and ride home on a singlespeed.