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Bent Derailleur Hanger

Last Wednesday evening while riding a night-time backwards lap of The Pines at Stony Creek I clipped a tree and fell over. This normally wouldn’t be notable, except someone was following me so closely that as I fell he ran into me, then ran over and fell on my bike. Everything initially looked fine on my bike and neither of us were hurt, but upon later inspection I found the derailleur freshly scratched and it appeared that the derailleur hanger was bent inward, causing a bit of extra drivetrain noise and weirdness.

Tonight I pulled things apart and checked the derailleur hanger, and as shown above it’s bent. Thankfully I had picked up a spare earlier in the year (#82 from so I was able to fit it and get things back to normal. Bent derailleur hangers can cause all sorts of strange issues, because once bent the derailleur (which moves and tensions the chain) is no longer working on the same plane as the cogs, so it exerts twisting forces on the chain as it transits between the cassette and jockey wheels. This usually causes frustratingly erratic shifting that’s impossible to adjust away.

Park Tool sells the DAG-2 for aligning derailleurs to wheels (and thus cassettes), but for thick, single bolt derailleurs (such as mine) it’s generally difficult to impossible to properly straighten one. Replacement is really the best option.

For reference, the new, unbent derailleur hanger can be seen with the straightedge (as above) here.


  1. James
    James September 22, 2010

    When I bought my bike it came with a spare hanger. The bloke in the shop said “keep that safe, you’ll need it one day after you’ve fallen off”.

  2. c0nsumer
    c0nsumer September 26, 2010

    James: I’ve now taken to carrying one in my bag, just in case. This past summer I turned a friend’s bike into an ad-hoc scooter after he ripped his derailleur hanger off and didn’t have a spare, and friends have related stories about being five miles out on rough trail when a hanger is broken. Since they only weigh a few grams I have no good reason not to keep one in my bag along with the tube, patch kit, pump, multi-tool, cable ties, and other trail-side repair items.

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