Any downside to using a dynohub made for a 26"/700c wheel on a 20" wheel?
Can I use a 36h Disc dynohub designed for a 26"/700c wheel? Are there any drawbacks to doing this?
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Replies to This Discussion
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Permalink Reply by Matt M. 18.5KM on
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Oh wow, there is some writing on this.... So Peter White says to use Schmidt dynohubs since the drag on Shimano hubs is much higher on 20" wheels. Given that fact, and if price is a consideration, an SP (Shutter Precision) hub would be the obvious second choice since they are said to have drag which is close to or exceeds an SON. Follow the links and you'll find precisely what you need.
So many other things crop up when switching to this setup. You ask questions like "Can I charge up my cellphone, gps, and just random batteries while I ride? Can I run a tail light, and does this light have to be an AC dynamo light or can I use my old blinky lights with no batteries?" etc. etc. etc..... Soldier on, man.
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Permalink Reply by Doug Haynes on
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I had a friend who had an Alphine in a 20" on a Bullitt and it worked fine.
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It really is a matter of preference I guess. Peter White on some level is quite anxious to sell more SON hubs. But it looks like Alfine costs a bit more than SP.
Here us a glowing review for the latest and greatest Shimano dynamo:
http://www.gravelbike.com/?p=350
notoriousDUG said:I had a friend who had an Alphine in a 20" on a Bullitt and it worked fine.
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Permalink Reply by Duppie on
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I do have a Son 28 on my "nice" bike, and a SP PV-8 on my daily commuter. My wife uses a Sanyo dynohub on her daily bike. All 3 bikes run both a front and taillight off the dynamo hub. I do like both the SON and the Shutter Precision. I would say a SON is so expensive that it's use is limited to a truly high end bike. The Shutter Precision at less than half the cost suffices for almost any bike.
The question was around any negatives on using a 28" dynamo on a 20" wheel. I've read some articles that say that the drag would be higher than needed, since the smaller wheel turns faster at the same speed.but i haven't read anything definite on this topic.
Matt M. 18.5KM said:Oh wow, there is some writing on this.... So Peter White says to use Schmidt dynohubs since the drag on Shimano hubs is much higher on 20" wheels. Given that fact, and if price is a consideration, an SP (Shutter Precision) hub would be the obvious second choice since they are said to have drag which is close to or exceeds an SON. Follow the links and you'll find precisely what you need.
So many other things crop up when switching to this setup. You ask questions like "Can I charge up my cellphone, gps, and just random batteries while I ride? Can I run a tail light, and does this light have to be an AC dynamo light or can I use my old blinky lights with no batteries?" etc. etc. etc..... Soldier on, man.
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I heard the Sanyo hubs are bomb-proof but have higher drag than other brands, perhaps they smoother running than a Sturmey Archer, I don't know, but I'd be looking at Sanyo before SA.
So, to directly address your question from everything that I've read, modern dyno lights have overvoltage protection. Even if your 20" wheel runs at a higher RPM and cranks out more voltage, overvoltage protection will stop the dyno from blowing out your light. So I think that's really the only issue. I spent a long time researching the subject, and I can't see why you would have any problems.
It looks like there are laws in Europe backing me up on this. Here is a paragraph from Peter White's page addressing the issue. What I'm saying is that the opposite is true going from a larger wheel to a smaller one - you'll always have plenty of light even at very low speeds.
"In January, 2010, Schmidt changed the name of the SON20R to SONdelux. Skip this paragraph if you aren't interested in German bicycle lighting regulations. ;-) The reason for the name change is a bit complicated. German law regulating bicycle lighting is very strict. A dynamo powered headlight must reach a certain brightness at a certain minimum speed. If you use a hub designed for 20" wheels to make a wheel with a 700c rim, that wheel will be rotating at a slower RPM at a given speed than the same hub in a 20" wheel, so the hub's output will be lower. With a halogen bulb headlight, the light would not reach the minimum required brightness until you were going faster than the law requires. But with LED headlights such as the Schmidt Edelux, Busch & Müller CYO and others, this isn't a problem. You can use a hub designed for 20" wheels in a 700c wheel and the light will be very bright at low speeds. Previously, it was illegal under German law for Schmidt to sell the SON20R in Germany for use in 700c wheels. But the law has been changed, provided the customer also buys a LED headlight. So now, Schmidt can sell the SON20R for use with 700c rims, as long as the wheel is used to power certain LED headlights that produce high output with very little power. So there's no longer any need to call the hub a "SON20R", implying it's only suitable for 20" and smaller wheels. Hence, the name change to SONdelux."
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Permalink Reply by BobbyK on
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I've been running a Sram D7 dynamo on my cargo bike with a 20" front wheel, and built up a few other 20" dynamo wheels with SP and Alfine hubs. All have worked just fine.
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You would get more drag. You could compensate with narrower tires or pending on rim size of you're using BMX spec 20x1.75, you could get the slightly larger and narrower 20 x 1 1/8 or 20 x 1 3/8. You'll want to look into 'mini bmx racing' tires/rims as well as recumbent as that rim size is used in mini bmx. I would recommend shutter precision hubs(usually in stock and well enforced at yojimbos for their low rolling resistance) or shimano also has low rolling resistance, however you can get SP's hub in 28 hole to further reduce weight and compensate resistance. Ive been looking into this myself as well to do the ultimate rebuild on an old Italian folding bike to go on adventures and to keep in my trunk for chaotic road trip emergencies. Cheers. -Nate
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Permalink Reply by Christopher Wallace on
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Keep things simple, Get a new rim for a hub designed for a 20" wheel.
Four spokes are all that is needed to take all the loads a wheel dishes out, If you have more than 4 spokes then you will be just fine. A wheel with 32 or 36 spokes do not matter when the spokes are evenly and correctly tensioned the wheel will last for years of normal riding.
Abuse will kill a wheel in an instant, running through a curb or huge pothole, or a motor vehicle crushing it, etc will destroy the strongest wheel.
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Finding a dynamo hub specifically for 20" is making it more complicated...
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Shutter Precision makes a disc version of their 20" hub, but only in 32h. And my hub is 36h. So the options are to either use the existing rim with hub for a 700c wheel or buy a new rim and get the correct hub for a 20" wheel. I'll have to dig up my old Bicycle Quarterly's to see if increased drag would make it worth the extra effort and cost.
Nate Bell said:Finding a dynamo hub specifically for 20" is making it more complicated...
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32h rim in 20 x 1 1/8 size shouldn't be too hard. I'd recommend looking for new old stock rims on eBay as they are usually very cheap
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Here is a new disc 36H rim, a Sun Ringle with spoke eyelets. A real beauty, IMHO.... Hope that nails the problem. Shutter Precision says there IS a 36H version of the PD-8 for 20 inch wheels..... so.... is that the answer?
"The S-Series dynamo hubs are not only the smallest physically, but are the lightest weight on the market at 360g. This model is designed for 20" wheels at a 6V3W rating. It is also ready for use with 700C wheels at 6V2.4W output.
Enjoy small and light..."Nate Bell said:
32h rim in 20 x 1 1/8 size shouldn't be too hard. I'd recommend looking for new old stock rims on eBay as they are usually very cheap
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