How to choose the right derailleur hanger

The derailleur hanger is exactly what it sounds like – it's the component attached to the rear dropout of your bike frame that the rear derailleur bolts on to. If yours breaks, here's how to choose the right replacement.

The derailleur hanger's job 

Also known as a called a mech hanger – the derailleur hanger is sometimes integrated into your bike's rear dropout, but it's usually a separate part, most often made of aluminium. The top end is screwed to the frame while the derailleur fixes to the other end.

A replaceable derailleur hanger is what's know as a sacrificial component. It is designed to bend or even break if, for example, your bike falls over on to the right side, helping to avoid damage to the frame and rear derailleur.  

You can often re-straighten a derailleur hanger or, if it does need replacing, a new one is inexpensive, whereas damage to a frame or rear derailleur is much more serious. 

What to do if your derailleur hanger gets damaged

The most common damage to a derailleur hanger is that it gets bent inwards. If this happens, it's worth trying to bend it back. 

First remove the rear derailleur with an Allen key, then use the jaws of an adjustable spanner to gently bend the hanger back to its original shape.

Aluminium doesn't particularly like being bent back and forth so there's a chance that the hanger will break in the process, but if it goes back into position with no obvious flaws you can reattach your derailleur. You should then check that it shifts correctly across the cassette without the chain coming off either end.

Choosing a replacement derailleur hanger

If the derailleur hanger can't be bent back into shape it's time for a new one. Any derailleur hanger will work with any derailleur, but there are loads of designs out there that are particular to different frames. 

The hanger that's suitable for most B'Twin Facet, Mach, Alur, Van Rysel Ultra and Triban road bikes, for example, is different from one designed for a B'Twin Riverside Hoprider hybrid bike.

The type of derailleur hanger you need for Rockrider mountain bikes differs between models. The listings on our website tell you which bikes a hanger is designed to fit.

If your bike is sold by Decathlon, find it on our website and scroll to the bottom of the page. In the 'Maintenance and repair' section there's a 'Spare parts' button that'll take you to all the relevant replacement components, including the derailleur hanger you need.

Replacing a derailleur hanger

Replacing the derailleur hanger can often be straightforward. Remove the rear wheel from your bike and take off the rear derailleur with an Allen key. Then remove the damaged hanger from your frame – it's usually held in place by either one or two screws – check that there's no damage to the dropout and give it a clean.

Put a little grease on the surface of the dropout (there will probably be some dry threadlocker already on the new screw threads) and tighten the new derailleur hanger in place.

Once you've attached the rear derailleur and put the wheel back on your bike, check the alignment. Looked at from the back of the bike, the line of the chain should be straight as it runs over the cassette and through the jockey wheels on the rear derailleur. If it isn't, you can remove the rear derailleur and bend the new hanger gently with something like an adjustable spanner.

Check that the shifting is correct and that the chain doesn't come off either end of the cassette. It could be that you need to make some adjustments using the rear derailleur's limit screws and the barrel adjuster. If you're in any doubt about how to do this, the technicians at your Decathlon store can do it for you.