Any downside to using a dynohub made for a 26"/700c wheel on a 20" wheel?

Replies to This Discussion

Permalink Reply by BobbyK on December 28, 2014 at 8:22pm

I would agree that it is not worth stressing over finding a 20" specific dynamo hub. Any increase in drag is going to be so small that you probably won't notice it. And, let's be honest, if you're riding a 20" front wheel, speed is probably not your main concern.

That being said, I also don't think you should be limiting yourself to a 36h hub. Building a wheel with a used rim is usually not the best idea to begin with, and a 32h 20" wheel is PLENTY strong. The spokes are so short and the effective flange diameter is so large(due to most dynamo hubs having relatively large flanges and the fact that you'll probably want to lace it 2-cross to get a better spoke angle) that it will probably be stronger and stiffer than 90% of the 36h or even 40h 700c wheels out there. Also, building/truing can be a pain in the ass since there is very little space between the spokes with a 36h 20" wheel. I have a Sram dynamo hub laced to a 20", 32h Velocity Aeroheat rim on my Soma Tradesman. I've carried well over 200 lbs on the front of that thing on many occasions, over rough Chicago streets(and even a cyclocross race). It is still dead true. 

And Nate; Although 20x1-1/8 (451bsd) is a neat size, there aren't really very many tire options that would be appropriate for a cargo bike. Stick with 406bsd, get a Schwalbe Marathon Plus, and be done with it. 

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Permalink Reply by Duppie on December 29, 2014 at 9:33pm

That PDF is the only reference to the existence of a 20" in 36h i have seen. In real life it appears to be a bit of a mythical beast.

Matt M. 18.5KM said:

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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Permalink Reply by Matt M. 18.5KM on December 29, 2014 at 9:45pm

Then get creatively and politely persistent.....!  :-)  Call the distributors...call call call callllllll.....etc....email....text.....politely text.....

California

650 871 8870

www.merrysales.com

U.K.
44 (01353) 662662

www.ison-distribution.com

Duppie said:

That PDF is the only reference to the existence of a 20" in 36h i have seen. In real life it appears to be a bit of a mythical beast.

Matt M. 18.5KM said:

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

• ▶ Reply

Permalink Reply by ad on December 30, 2014 at 9:26am

For what it's worth, Smart Bike Parts has been able to order seemingly-mythical parts for me from merrysales in the past.  In my case, it was a 1-inch lugged steel fork made by IRD.  
Matt M. 18.5KM said:

Then get creatively and politely persistent.....!  :-)  Call the distributors...call call call callllllll.....etc....email....text.....politely text.....

California

650 871 8870

www.merrysales.com

U.K.
44 (01353) 662662

www.ison-distribution.com

Duppie said:

That PDF is the only reference to the existence of a 20" in 36h i have seen. In real life it appears to be a bit of a mythical beast.

Matt M. 18.5KM said:

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

• ▶ Reply

Permalink Reply by Duppie on January 4, 2015 at 1:54pm

Finally dug up the old issue of BQ. While drag does increase at higher speeds, it should not be noticeable. By my guess it would go from less than 1% to less than 2%. Combine that with LEDs not being at risk for burning out, and using a 700c hub should not be an issue.

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Permalink Reply by Matt M. 18.5KM on January 4, 2015 at 5:14pm

...which makes the search much more manageable.  Good luck on the build - may you have no popped spoke nipples and a quick true.  Do you use spoke prep or linseed oil?

Duppie said:

Finally dug up the old issue of BQ. While drag does increase at higher speeds, it should not be noticeable. By my guess it would go from less than 1% to less than 2%. Combine that with LEDs not being at risk for burning out, and using a 700c hub should not be an issue.

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