dynohub designed for 20" wheels in a 28" wheel size?

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RC
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Joined: 28 Sep 2007, 12:46pm

dynohub designed for 20" wheels in a 28" wheel size?

Postby RC » 30 Oct 2013, 9:19pm

Dear all, I have an old Schmidt dynohub designed for use in my 20" wheel touring bike. I'm using this bike less and less and I wanted to ask your advice about whether this hub would work in a larger wheel (700c). The power output will be less for a given speed I guess, but does this matter with modern LED lights now? I'm rubbish at building wheels so will have to take the hub to my local bike shop which will cost a few quid, any ideas if this will work?

Thanks for any advice!

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Mr. Viking
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Joined: 6 Jun 2012, 9:29pm
Location: Liverpool

Re: dynohub designed for 20" wheels in a 28" wheel size?

Postby Mr. Viking » 30 Oct 2013, 10:14pm

The larger wheel will rotate at 70% the rate of the smaller wheel for any given speed. This means that the light will not reach full brightness until a slightly higher speed. In my experience with dynamos they reach full brightness slightly above walking pace so this shouldn't be an issue. I've only used bottle dynamos, but I can't see how a dynohub would be any different

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531colin
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Location: North Yorkshire

Re: dynohub designed for 20" wheels in a 28" wheel size?

Postby 531colin » 30 Oct 2013, 10:24pm

Schmidt 20R dynohub was originally specified for 20" wheels, but now is approved for 700c to the German industry standards .....they are more than good enough for LED lights.....http://www.spacycles.co.uk/products.php?plid=m2b0s133p1093

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meic
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Location: Caerfyrddin (Carmarthen)

Re: dynohub designed for 20" wheels in a 28" wheel size?

Postby meic » 30 Oct 2013, 10:29pm

It is a popular "trick" with faster riders. The dynamo is built to meet the German regulations that want adequate light output at just above walking pace. Fitting a 20" type hub will mean that you have a lower resistance at any given speed but if you are a faster cyclist you will easily be producing enough power for your lights.

Tourers on the other hand tend to be a bit slower and often want extra electricity production for charging their toys. So they wouldnt want to use the lower power hubs.
Yma o Hyd

RC
Posts: 38
Joined: 28 Sep 2007, 12:46pm

Re: dynohub designed for 20" wheels in a 28" wheel size?

Postby RC » 31 Oct 2013, 7:47am

That's great! Thank you for your replies. I'm going to use it just for a front LED light, with a back up flashing front light for visability.
Cheers