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Oct 27, 2023

How to Fix a Bent Derailleur Hanger

Jim’s Tech Talk By Jim Langley A few of you asked me to cover repairing bent derailleur hangers so that’s the topic for this week and next. It’s a good problem to understand because it doesn’t take

Jim’s Tech Talk

By Jim Langley

A few of you asked me to cover repairing bent derailleur hangers so that’s the topic for this week and next. It’s a good problem to understand because it doesn’t take much to knock a derailleur hanger out of alignment. Even something as seemingly harmless as putting your bike in the back of a truck or hatchback with the bike’s drive side down could bend it. Or, having your bicycle fall over and land on its drive side.

And with our modern 11-speed drivetrains and precision electric derailleurs even minor hanger bends can cause annoying shifting problems, such as hesitation, overshifts and noise.

Kind of a sad story but the most recent derailleur hanger disaster I witnessed happened to a rider I befriended while we were both riding around Lake Tahoe. Closing in on the 9-mile Spooner Summit climb on the Nevada side, a person on a construction crew stepped into our path. I swerved to miss her, crashed into my new friend and we both went down in a pile.

The bikes seemed okay and the construction site had a good first aid kit to patch up our road rash. But, as soon as we hit the first ramp, my friend went to shift and the derailleur shot straight into the rear wheel breaking several spokes, mangling the derailleur and even worse, shearing off his derailleur hanger. He called home for a ride and I continued but not before apologizing for not looking at his bike more closely.

In case it’s new bike lingo to you, the “derailleur hanger” is the part of the bicycle frame that the rear derailleur attaches to. It’s a smallish tab that’s either part of the right rear dropout or attached to it. In the photo here the hanger is the silver part stamped with a “W.” You can see the heads of the small screws that attach it to the dropout. Oh, the “dropouts” are the part of the frame that the wheel axle fits into to attach the wheel to the frame.

The rear derailleur is attached to the derailleur hanger with a bolt. Because the rear derailleur sticks out from the side of the bike, it’s one of the first things to hit the ground in falls. Since the derailleur is much larger than the derailleur hanger it acts as a long lever and can easily overpower and bend the hanger.

Adding to their vulnerability, most derailleur hangers today are made of aluminum (the one in the photo above is titanium). But even when most road bikes were made of steel, bent steel hangers were still a common problem. Luckily, most bikes today use replaceable derailleur hangers. They’re bolted on and can easily be replaced if they’re badly bent or broken. A good source is https://derailleurhanger.com/.

Two common signs that your hanger is bent are 1) suddenly the shifting is not working the way it was; and 2) the specific problems caused by a bent hanger are hesitation shifting into the smallest rear cog along with shifting over the largest cog and into the spokes.

Or, if it’s only bent a little, the derailleur might not throw the chain off the cog or into the spokes, but it might touch the spokes when you’re riding, making a tick, tick, tick noise as it hits each one.

If you experience these symptoms you should stop and visually check the hanger alignment. To do this, stand directly behind the bike kneeling or stooping so you can see the cassette cogs, derailleur pulleys and chain.

On a perfectly aligned hanger, an imaginary straight line will bisect the cog the chain is on and both derailleur pulleys. When a hanger is bent, that imaginary line won’t be straight. You can clearly see this in this photo from Park Tool’s page on derailleur hanger alignment.

Here are a few ways to fix or try to fix bent derailleur hangers on the road. I’m assuming that you didn’t shift into the spokes and break some and/or bend the derailleur itself. Or that you didn’t damage the dropout.

NOTE: Make sure the wheel is securely clamped or bolted in place before straightening derailleur hangers. The axle reinforces the frame so it’s safe from the bending forces. Before working on a bent hanger, shift the derailleur onto the smallest chainring and cog. This is best for sighting the alignment and it takes most of the tension off the chain.

If you have a replaceable derailleur hanger, the best way to deal with a bent one when riding is to carry a spare hanger and simply replace the bent one. The part is so small and light you won’t even know you’re carrying it. Be sure to carry the right tools to remove and install the hanger.

Again, this assumes that the only thing damaged is the derailleur hanger. If you replace it and the shifting is still glitchy, then it’s likely that the derailleur also got bent, which is a different problem that’ll need to be addressed.

If you don’t have any tools (keep reading), you can try to straighten a bent hanger with your hand. The photo shows how to hold it. You want to pull out focusing on bending ONLY the hanger not any part of the derailleur.

Be very careful not to pull too hard at first. You might only need to move the hanger a small amount. Sight from behind, try pulling a little and look again to see if you improved the alignment. Then repeat until you’ve got the imaginary line bisecting the cogs and pulleys.

In the photo I’m using a 3-way hex wrench inserted into the derailleur bolt. This gives a nice purchase and directs the straightening force exactly where it’s needed. A standard hex wrench will work too, but the longer the better for the best leverage.

If you carry a medium adjustable wrench, they provide excellent leverage for straightening bent hangers. But you must first remove the rear derailleur.

Be careful removing rear derailleurs after bending a hanger. If the threaded part of the hanger was damaged or if the derailleur bolt was bent, it can be difficult to remove the derailleur. If you force it, you might strip the threads on the hanger or even the derailleur.

While it might be easy to replace a replaceable hanger, it might not be so easy to replace a stripped derailleur bolt, which might mean needing to buy a whole new derailleur. To avoid this, if the bolt won’t turn easily, leave the derailleur in place until you can get home and better assess what the problem is and fix it.

If you have a rear wheel with a threaded quick release axle, it’s likely that the axle thread is a standard 10mm thread, which is the same as what’s in derailleur hangers.

This means that you can use your wheel as an alignment tool. To do it, you must remove the rear derailleur. You can then remove your wheel quick release, screw the end of the axle into the hanger and hold onto the wheel using it as a giant lever to straighten the hanger. Be sure that the axle fully threads into the hanger. If it’s only held by a couple of threads it’ll probably pull out (strip) the hanger threads – so don’t use the wheel.

Note that with this technique the wheel isn’t in the frame reinforcing it anymore. So you must be careful not to bend anything other than the hanger. If you’re riding with someone maybe they’ll let you put their wheel in your frame while you make the repair.

As long as the wheel and frame wasn’t damaged, you can usually get home with a bent derailleur hanger. Just remember not to shift into the largest cog. Since the hanger is bent the chain might make a chattering noise on the misaligned pulleys but you can usually find gears that align the chain enough that it isn’t so bad you can’t keep riding.

Next week, I’ll show you my favorite professional hanger alignment tool and how it’s used. In the meantime, please share your favorite on-the-road alignment tips and tricks. Also, here’s Park Tool’s excellent article on hanger alignment using their tool: https://www.parktool.com/en-us/blog/repair-help/rear-derailleur-hanger-alignment.

Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.