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I want to buy a Shimano hub dynamo, but I'm encountering problems getting a bike shop to commit to installing it for me if I buy it. So I have a couple questions that I'm hoping some of you guys might be able to help me out with.

  1. Can a wheel be rebuilt replacing the old regular hub with the dynamo? Or does this require a new wheel to be built? (I've heard once that it's difficult to rebuild a wheel with a rim that has already been built before).

  2. If you can rebuild a wheel, and the hub is a bit larger in diameter than the old hub, do the spokes need to be replaced/shortened, or can they be still be used? Is there some guideline or rule of thumb about the length of a spoke as long as they're all consistent?

  3. Is the installation of a hub dynamo the same as a standard hub? I know that the hub has a lot of moving parts inside, but it seems no different on the outside, and I wonder if there are special steps or considerations when installing.

I appreciate any info anyone can give me! I feel like these bicycle shops have simply never had any experience with a hub dynamo and their first reaction is just "no".

Edit: As a side question, does anyone have any experience with wheel building? Is this a straightforward process? This is something I wouldn't mind learning how to do. Is this the kind of task where you can destroy a wheel or two in the learning process, or will I just need spend more time adjusting to get it right as I learn?

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You can "rebuild" using an existing rim, but rims are relatively cheap (and it would be foolish to try to reuse the spokes). Better (and perhaps cheaper) would be to buy a suitable wheel already built with the dyno in it. –  Daniel R Hicks Jan 15 at 22:38
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Wheel building is something that a reasonably competent, mechanically inclined, and, most importantly, patient person can learn to do, but a dyno hub is probably not the right place to start, since the shorter spoke length makes the job more difficult. –  Daniel R Hicks Jan 15 at 22:40
    
I've built hub dynamo wheels. Unless it's a small wheeled bike like a folder, the shorter spokes aren't going to make a significant difference. It's still a symmetrical front wheel, which is easier than a back. Well, unless it's a Sturmey Archer rear wheel combined dynohub and hub gear. –  armb Apr 9 at 11:10
    
It is, in theory, possible to destroy a rim by massively overtightening the spokes when building the wheel. But it's unlikely. What you can do on some dynamo hubs is break the internal wiring by turning something that looks like it might adjust the bearings - make sure you read the manual for your hub. It probably has sealed bearings you can't adjust anyway. –  armb Apr 9 at 11:19

1 Answer 1

up vote 3 down vote accepted

Briefly:

1) yes, you can re-use the existing rim.

2) yes, you could shorten the existing spokes, but that would be expensive and foolish.

3) The installation is the same except now you have wires so you need to plug them into the hub too.

The main issue is (2). Spokes are usually only reused when the rim is being replaced with an identical rim (usually a new one for a worn one), and even then most wheelbuilders will prefer new spokes. Spokes bend a little as they're built into the wheel, and getting those bends in exactly the right place when you rebuild the wheel is effectively impossible. So you'll build the wheel, ride it a little, the spokes will bend back and you'll have to re-tension everything. Usually more than once. If you're paying someone to do this it's cheaper to just buy new spokes.

It's possible to shorten spokes, there are spoke cutting tools for this. They're normally used to make really short spokes (for putting a dyno hub into a 16" wheel, for example) but these days it's possible to buy spokes online in almost any size. But you could sit there and shorten all the spokes in your wheel. But again, if you're paying someone else to do this for you it will be more expensive than a new set of spokes. The tool is also much more expensive than a set of spokes.

If your rim is in good condition that's the bit to keep. If it is worthwhile, you may be better off selling the whole wheel and buying a new rim anyway.

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Just want to add that for the spokes, cutting is a pain because one end is (usually) bent and the other is threaded. Cutting removes one of these ends and then you have to recreate it. –  Aaron Jan 15 at 21:07
    
Thanks for the great info! –  Julian Cleary Jan 15 at 21:33
    
Yep. Just build a new wheel. –  andy256 Jan 15 at 22:34
    
As far as I know, they do have to be special ordered in most places - especially for people who don't live in an area with a quality LBS. One place (for the US anyway) is Peter White cycles (peterwhitecycles.com). –  Batman Jan 16 at 3:23
    
Or starbike or one of the other online shops –  Mσᶎ Jan 16 at 3:50

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