On many mountain bikes and bikes designed to take some punishment, the derailleur hanger is made of a different metal and is softer than the rest of the rear frame. It is designed to be a sacrificial piece that will break when the derailleur strikes something solid.

The picture on the right shows a very expensive Shimano XTR derailleur mounted to a bike. The derailleur hanger is the black piece that is attached to the white triangle of the frame. The derailleur is attached to the hanger with an pivot mount. When the derailleur hits something like a rock, the hanger will bend and in extreme cases it will break right off.

One thing I've learned is to always keep a spare hanger around. In one instance it took us more than three weeks to get a derailleur hanger for a Canondale bike.

On the right you can see the broken derailleur hanger on my StumpJumper bike. What often happens in a case like this is that the remaining part attached to the bike is also bent and it can be stuck and can be so tight that it is hard to remove the Allen bolt holding the hanger to the frame.

I had to use a metal saw to cut grooves in the side of the hanger to relieve the stress on the bolt to loosen it enough that I can remove it.

Now that the new hanger is attached to the frame, it is time to tackle the hanger on the derailleur itself. Here you can see part of the benefit of the derailleur hangers. For about $20 I can get my bike as good as new. If the derailleur hanger did not break, it would have been much more expensive to replace my SRAM X-0 derailleur, or fix a damaged frame.

To remove the broken hanger from the derailleur, I used a large Allen wrench. Since the hanger was bent in the accident, it took a bit of force to remove it from the hanger.