Safety Derailleur Hanger project-
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  1. #1
    mtbr member
    Join Date
    May 2011

    New question here. Safety Derailleur Hanger project

    Hey everyone.
    I was biking a little while back and visited my friend's house, where we decided to have a quarter-mile sprint race, just for fun. I had a 4 year old aluminum frame mountain bike that had never been in an accident. I shifted to a low gear for the start, but a few strokes in, my hanger sheared off and my rear derailleur flew straight into my spokes. Back wheel locked up, and I almost slid into the curb. I ended up breaking 2 spokes, damaging 3 or 4 more, and annihilating my derailleur.

    I'm not sure how much this happens, but a good friend of mine has also had the same problem, and I've seen lots of pictures of the same happening on the internet. I ended up spending half nearly half the price of my bike on repairs.

    I know that hangers are designed to shear off to protect the frame and derailluer from damage, but it seems that after it does, it's moving with substantial freedom and it has a fairly good chance of getting caught in the rear wheel and getting ripped apart. I decided to tackle this problem for an engineering class, and I thought perhaps one could incorporate some sort of integrated retaining mechanism into the hanger construction so that when it experienced too much load and sheared, the derailleur could be kept in place and prevented from damaging the rest of the bike and itself.

    I have some ideas in mind for the specific mechanisms, but since you're all much more experienced at bike maintenance than I am, I was wondering if any of you had any suggestions.

    Also, we need to collect survey data for the class, so I'd really appreciate it if all you were to complete a short online form I've prepared.

    Thank you!

  2. #2
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    filled it out, but the form sucks.

    For one, the hanger for my new bike isn't on the list. I had to use my old bike, which I have bent the hanger several times. Never sheared as in your example.

    I don't see how you could accomplish your goal effectively. The sheared hangers I've seen in the shop USUALLY fail in the same place - right where the hanger meets the frame/dropout. Sometimes the break occurs inside the dropout of the frame. This tends to be where material on the hanger is thinnest. From what I've seen, a few things tend to cause this.

    One would be a crash. Not much you can do about that, except not crash. Crashing can be expensive, and where your derailleur goes when the hanger breaks should be the least of your worries.

    Another occasion, specific to mountain bikes, relates to trail debris. Usually a stick in my area, gets tangled up in the rear derailleur and rips it off as you ride by.

    The other way (and most common, IME) is lack of maintenance or poor maintenance. Poor derailleur adjustment allows the rider to shift the derailleur into the spokes (not the hanger's fault - that's all on the rider - in fact, the hanger breaks AS A RESULT). Also in this category would be that the rider lays the bike down on the drive side, or stores the bike somewhere that the hanger gets bumped/tweaked, which allows the rider to shift the derailleur into the spokes. Again, the hanger shears off because the bike was out of adjustment and the rider failed to notice before it became an expensive problem.

    IF you could engineer a solution, the only scenario I see it working for would be the second trail debris scenario, which is less common, IME. Based on where the shearing occurs, I just don't see how you could add material that would prevent stuff from going into your wheels.

    Along this vein, though, there ARE products out there that did something similar. Specialized made these things for awhile.

    Name:  specialized-derailleur-guard-demo-enduro-hanger-42584.jpg
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    Safety Derailleur Hanger project-622613273_o.jpg

    and I've seen a few other variations on this concept made by other manufacturers.


    I don't know how effective they are/were.

  3. #3
    Professional Crastinator
    Reputation: Fleas's Avatar
    Join Date
    Jan 2006
    We have stuff at work that aligns using magnets. Some of those magnets are very strong, but magnets are heavy.
    Tantalum can bend 1,000 times without breaking, but that's expensive.
    Maybe a ball-and-socket connection encapsulated in a flexible material. It could break away, but still be retained in close proximity to its mounting point. The rider would then re-set it in its joint.

    btw - that form is very limited. My last drlr failure was from a stick coming off the front tire. The drlr broke off and the hanger was bent, as well as 3 spokes. The chain was also damaged. The hanger did not break. I even straightened it and re-used it.

    The solution is probably Tioga/Sugino tension disc wheels for everyone.

    It's never easier - you just go faster.

  4. #4
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
    Join Date
    Nov 2007
    I didn't fill out everything. My 'A' bike is a '13 Kona Hei Hei DL. My old bike, and the one I've broken hangers on, is a '07 Specialized Hardrock.

    The simplest solution that springs to my mind is materials selection. I'm not sure which alloy and heat treatment derailleur hangers use. But something really malleable might work better. It won't stop them from failing, but if they can get more bent and mangled before actually rupturing, maybe that will help with the catastrophic failure scenario.

    You might also consider some kind of a composite construction. Like aluminum for stiffness and steel fibers for better tensile strength without messing with the bending strength of the hanger. Where they were placed would be important and it wouldn't prevent failure due to shear around the holes but like Nate says, that's not where these things tend to fail.

    Honestly, it would be a pretty hard sell for me. I see crashes as an "all bets are off" situation. Although one of the two derailleur hangers I've killed was due to extreme chain suck. But it's kind of a cool problem.
    "Don't buy upgrades; ride up grades." -Eddy Merckx

  5. #5
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    ummmm... Just keep your bike adjusted and in good shape.

    It is MUCH more likely that your RD went into the spokes THEN the hanger broke because of it. Not the other way round.

    The hanger could have been bent before the failure, but that is a issue with hangers being too soft.
    The trouble with common sense is it is no longer common

  6. #6
    Reputation:'s Avatar
    Join Date
    Nov 2013
    that is what the dork disc is for

    -----------------make a huge dork disc, problem solved---------------------

    or, educate... and laminate a easy to read card on how to adjust rear derailleurs so it doesn't happen

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