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I'm building a bike on an old aluminium frame that is missing the rear derailleur hanger. I'm putting an IGH on it, so I don't need to use the hanger, but the dropout seems too thin without it. Can I do without, or is it necessary to avoid bending the dropout somehow?

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  • It does seem a bit counter-intuitive to fit something that is otherwise redundant. However I know aluminium can be a tricky material to work with, so if you are considering realigning the dropouts I would seek expert advice before doing so.
    – PeteH
    Nov 30, 2015 at 18:48
  • Gidday and welcome to SE Bicycles. A washer may be all you need to "thicken" the dropout so the QR skewer can bite. If its nutted then probably don't need anything. Remember the hanger is not a structural part of the frame, its just a hook for hanging the rear mech.
    – Criggie
    Nov 30, 2015 at 19:25
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    I would try very hard to find a replacement hanger, since they're usually not every expensive. BBB have a catalogue of about 100 different shapes so it's worth taking a photo of the dropout of your bike and sitting on their website comparing the photo to the hangers trying to find the right one. Or search online for your bike and see if that helps. So: can you add a photo of the dropout (ideally square on, ie camera out along a line extending through the axle of the rear wheel, and either a photo of the bike or preferably the make and model details.
    – Móż
    Nov 30, 2015 at 21:07
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    Sorry, Wheels Mfg for the derailleur hangers and they have more than 160 of them :)
    – Móż
    Nov 30, 2015 at 21:34
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    Well, I just realized the IGH needs a chain tensioner for my vertical dropouts, so it looks like I need the hanger after all! Thanks for the input. Dec 1, 2015 at 5:00

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Most aluminum frames have a replaceable derailleur hanger, which typically is part of the dropout itself as you can kind of see in this image:

enter image description here

Without it, the dropout is indeed too thin and your spacing is messed up, not to mention that the strength of the dropout is decreased. You need to identify the correct replacement hanger and get it fixed.

Also, I don't know what IGH you're using, but it will most likely require some sort of chain tensioner as well, and without sliding dropouts or an Eccentric Bottom Bracket, you're probably going to need a spring-based chain tensioner that will bolt on to the derailleur hanger:

enter image description here

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