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My bike has a hub dynamo in the front wheel. Recently I have replaced the old fork with a used one I got from my local bike club. The new one has fixing points for the cabling on the other side of the fork. Because the hub has only one connector for the wires, it would need to be installed contrary to the indicated running direction.

I recently saw this question, and it is partially answering my question. To follow up: How, if at all, does the dynamo change the situation?

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The electric parts of the dynamo hub don't care. They're an AC generator and there's no concept of reversing the flow with AC.

However, the mechanical bits of the hub itself can be a problem. You don't indicate which manufacturer/model dynamo you have. The great majority of hubs are constructed such that they are expecting the wheel to turn in a certain direction in order to keep internal nuts and bolts tightened. Going in the opposite direction could lead to fiddly bits unscrewing themselves.

Where possible, I'd try to respect the directionality of dynohubs that have directionality. It would just take an extra length of wire or some zipties to snake the power cable around to the other side, it's worth that for the peace of mind to know that the hub won't self-destruct when you're going down a long hill.

Note: All Shimanos, all Sanyo, and older Schmidt/SON hubs are vulnerable to unscrewing if they are oriented with the power leads on the left (NDS) rather than the right (drive) side. Newer Schmidt SON hubs are flippable with the exception of the SON SL (below). When in doubt, ask your manufacturer/reseller.

N.B.: Some special (and expensive) dynohubs such as the Schmidt Son SL pair with specially designed forks so that no external wires are needed, but it also means you can't flip the wheel around or it shorts to ground. Assuredly that's not the case with you.

  • Great answer, thank you. I would suggest that you add the note about self-tightening nuts and bolts as an answer to the original question as well. Nobody raised that issue there yet and from a mechanical standpoint, it does make sense. – antipattern Jul 3 '17 at 12:31
  • It doesn't apply to regular hubs, which are reversible. Only dynohubs (which have the extra fiddly and sproingy bits inside). – RoboKaren Jul 3 '17 at 18:44
  • I did some research and the self-unscrewing applies to all Shimano and Sanyo hubs. Older Schmidts are also vulnerable. – RoboKaren Jul 3 '17 at 18:46
  • There are also systems for transporting humidity out of the hub which work in reverse (transporting humidity in) when run in reverse. I think it's in current Schmidt's, but I don't really remember the name, only the mechanism (there is a tube connected to one of the seals so that pressure differences are equalized through that tube only. The tube is wound around the axis of rotation so that its end always points in the direction of movement, so that gravity pulls drops towards the seal). – Nobody Nov 2 '17 at 17:23
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From the way a dynamo works in principle, I would expect it to work with either running direction. I would try that first and would not expect any long-term problems when it does work. If you provide details about the dynamo hub, maybe someone can comment on that model specifically. If it obviously doesn't work when turning backwards, I would change the cabling to the other side.

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