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What is the point of a rear derailleur hanger?

Posted: 27 August 2020 Tips & Tricks

Drivetrain/gear component detail on a titanium Bossi bike which is leaning against a graffitied wall

Why do derailleur hangers exist?

Before we philosophise on the point of a replaceable derailleur hanger, we should probably first clarify what it actually is.

A replaceable rear derailleur hanger is a machined piece of metal which attaches the derailleur to the frame.

Close-up of a bicycle cassette (rear cogs) and derailleur from the rear, an arrow indicating the rear derailleur hanger
This guy.

One very important -- and frustrating -- thing about hangers is that each one is shaped specifically to fit a particular frame. There's no one Trek hanger or Specialized hanger, etc.; each hanger is unique to each frame model.

As a result there are about a kabillion different shapes, and you need to know what shape yours is if you have to replace it. Hurray!

(Think we're kidding? Here's a small sample.)

Chart of rear derailleur hanger designs, showing that there are many, many, many different versions
C'mon, seriously?

So exactly what is the point of such a special piece of metal?

To frustrate bike mechanics!

We kid, we kid. The hanger's job is to sacrifice itself if your rear derailleur suffers an impact.

But why?

Well, it's a lot cheaper to replace a rear derailleur hanger than a rear derailleur.

So how do you know your hanger is bent?

If you've crashed your bike, there's a good chance it's happened upon impact. We also see a lot of bent hangers from bikes that have just fallen over while being propped against a wall or during an inattentive moment. (Hey, it's hard to hold your bike plus a coffee plus a bacon sandwich plus check out your Insta feed.)

Ask yourself: were my gears working OK before my bike hit the ground and now they're not? Then you've probably got a bent hanger.

What's that noise?

Your hanger is also definitely bent if you hear a tinny 'ting ting ting ting' noise while you're cycling. If this happens, STOP RIDING. That 'ting' sound is your derailleur brushing against your spokes. If your derailleur goes into the spokes, well, one of three things can happen (and sometimes all three things happen at once):

  1. You will rip your derailleur off.
  2. You will de-spoke your wheel in a spectacular and explosive fashion.
  3. You will have an unscheduled meeting between your face and the ground. And you did not RSVP to that meeting.

So consider 'ting ting ting' the death rattle of your ride until you can get your hanger sorted out.

The resulting damage to a bicycle wheel after the rear derailleur has gone into it, ripping out half of the spokes
Someone didn't listen.

Well, my hanger can't be bent because my derailleur hasn't been knocked.

If you've ever stacked your bike with a bunch of others outside a cafe, used a bike cage or locker at work, parked your bike in public, or put your bike into your car, there's a good chance either you or someone else has tapped the area, which is enough to put the hanger out and make your gears misbehave.

A jumbled pile of discarded bicycles
Yeah, your hanger's fiiiiiine.

Could something else have happened to it?

There's one other way to get a bent hanger, but it's less common: poor shifting technique.

Some hangers are particularly soft and even the force generated by shifting with too much load on the pedals is enough to send them out of alignment. To prevent this, pretend you've got eggs between your foot and your pedal when you're changing gears, until the gear engages.

In summary...

To keep your hanger safe, don't lean your bike's gears against or on top of anything, and shift with care.

Take care of your gears and they'll take care of you, because they sure do suck when they don't work.

Still having gear problems? We'll fix 'em for you.

Your hanger, just doin' its job.

What You Say

It's incredible! From the moment I took it off the bike rack, and put it on the ground, it made zero vibration sounds. Just the sound of raw tyre to brick knock, and a gentle chain clank to the derailleur cage. Gone were the standing-vibrations that rattled throughout the entire bike. I'm…Tom Bammann
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