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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?

1
  • Aside - fixing points can be substituted with zip/cable ties for testing, and if you want to make it permanent then there are small plastic mounting blocks that can be epoxied to the fork, or you can go all the way and have the same blocks brazed on ideally by someone skilled - it's not a task for a learner. Then paint to match and reinstall.
    – Criggie
    Jul 11 at 22:24

3 Answers 3

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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.

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  • 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. Jul 3, 2017 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, 2017 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, 2017 at 18:46
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    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, 2017 at 17:23
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I contacted Shutter Precision to ask if their PD8 hubs could be run backwards. Here is their reply.

Thanks for riding with SP. It is ok to put SP hub in your way. It is ok to spin backwards. It may create more power a little bit than it spins forwards. More power will will also creates more resistance. It is fair….So please fasten the quick release tightly enough. If the QR is not fastened tightly enough, the connector will spin when the wheel spins. When you ride, the connector cannot move. It must stay at the fixed position. Feel free to let me know if you have any inquiries.

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  • Funnily enough I just heard of an SP PD-8 being used successfully backwards in the back wheel, with a fixed cog on the 6-bolt rotor flange
    – Chris H
    Jul 12 at 11:09
  • This is a very interesting idea; do you have more information? The PD-8 is a 100mm hub, so I can't imagine how it fits in the frame. Jul 12 at 14:39
  • that was also my thought. I didn't get an answer. I can only guess an old steel track frame starting at 110mm cold set smaller. But it could have been a custom frame
    – Chris H
    Jul 12 at 14:48
  • There's a mention here of a 135mm SON for fatbikes. I don't think anything has been put on the web about the one I heard of
    – Chris H
    Jul 22 at 13:23
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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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  • I'm a big believer in justifying downvotes, and my reason here is that I think using your answer could lead to damaging a dynamo hub. Hope you're Ok with that.
    – pateksan
    Jul 12 at 12:47
  • @pateksan Please explain how running a dynamo backwards could damage it. A bike wheel runs backwards just when moving a bike around. Jul 16 at 12:51
  • I think the best possible explanation is already in the, now accepted, answer from RoboKaren: bicycles.stackexchange.com/a/47697/33048 and yes, bike wheels spin backwards when moving the bike around, but nowhere near as much as in riding. Unless someone moves their bike around more than they ride it.
    – pateksan
    Jul 16 at 21:40

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