Electronics, Lighting, & Gadgets - Shimano dynamo hub, 20" wheel, LED light: good idea?

So I'm trying to get my butt in gear for winter commuting. (Procrastinating again...) My old setup was an elderly Niterider single-bulb, which was OK except for trying to remember to recharge it, not overcharge it, not leave the battery on the bike when parked, etc, etc.

It looks like LED lights are relative equals of the old halogen lights, and hub dynamos have come a long way. I'd like a Schmidt hub, but they're twice the price of similar Shimano units.

My problem is that I'm on a recumbent with a 20" front wheel. According to the Peter White site: "There is no Shimano dynohub designed for 20" wheels. You can use it, but the drag will be considerably higher, since the hub is spinning at a higher rate." Is this truly an issue? I've heard several people say that they can't feel the drag on their Shimano hubs, so "considerably" times nothing is still nothing...

I have a 20" wheel with DH-3N30 lying in my hallway. Once I mount it, I'll report on practical experiences. However, one can make rough rule-of-thumb estimates.

Thus, a 20" wheel rotates 26/20, i.e. by 30%, faster than a 26" wheel. Say the drag will be about be 30% larger due to that, whether with or without electrical load. Now say you use a lamp such as B&M IQ Cyo that consumes just 1/3 of the electrical power of a halogen lamp. (In the estimate, I will ignore taillight.) Compared to a halogen lamp on a 26" bike, you will end up with a power loss of 1.3*(no-load power loss + (load - no-load)/3)=1.3*2/3*no-load+1.3*load loss/3 ~ no-load loss + 2/3*load loss. Given that the load loss for a dynohub may be 3-6 times larger than no-load loss, in the case of 26" and halogen, you should have about the same or smaller drag for an LED lamp and 20" as for a halogen with 26". With the lamp off, you will have more drag with 20" than 26", but still well less than for 26" with halogen on. Since you cannot really feel drag when riding in the latter case, I would not worry about the increased drag with 20".

I've got a shimano dynohub on a 20" wheel on my mini-velo and a Sturmey-Archer dynohub on a 20" wheel on my recumbent. Both are running LED head and taillights.

I do notice the drag from the Sturmey-Archer hub at speeds above 27kmh on distances of over 20km. It is slight, like a mild headwind.

Most of the time I don't notice any diffence at all. Most of the time I have to actually check to see if the lights are on during the day as I've forgotten to turn them off when I finish my night riding.

I've got a shimano dynohub on a 20" wheel on my mini-velo and a Sturmey-Archer dynohub on a 20" wheel on my recumbent. Both are running LED head and taillights.

I do notice the drag from the Sturmey-Archer hub at speeds above 27kmh on distances of over 20km. It is slight, like a mild headwind.

Most of the time I don't notice any diffence at all. Most of the time I have to actually check to see if the lights are on during the day as I've forgotten to turn them off when I finish my night riding.

Which hub do you have? My local dealer: http://www.universalcycles.com/shopping/product_details.php?id=10685 lists three different hubs, and it sounds like the current versions like these are somewhat improved over older hubs.

Which hub do you have? My local dealer: http://www.universalcycles.com/shopping/product_details.php?id=10685 lists three different hubs, and it sounds like the current versions like these are somewhat improved over older hubs.

Shimano: several year old DH-3N20
Sturmey Archer: two year old XFDD

shimano does not show a limit here. http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_2ZR0B_002/SI_2ZR0B_001/2ZR0B-001_DH-3N80_3N71-EN_v1_m56577569830616077.pdf

shimano does not show a limit here. http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_2ZR0B_002/SI_2ZR0B_001/2ZR0B-001_DH-3N80_3N71-EN_v1_m56577569830616077.pdf

Yeah, well... I get to find out when I get a hub. I also get to find out if overspeeding a Shimano dynohub is bad for LED lights- my first descent on my commute goes down a steep hill. I think I hit 35mph on it- which would drive the hub at the equivalent of 50mph on a 700C wheel.

Yeah, well... I get to find out when I get a hub. I also get to find out if overspeeding a Shimano dynohub is bad for LED lights- my first descent on my commute goes down a steep hill. I think I hit 35mph on it- which would drive the hub at the equivalent of 50mph on a 700C wheel.

I don't think so. I've deliberately gone for some night rides that include a couple of short but steep hills. I've got up to around 50kmh with the lights on and they haven't blown. yet.

I, personally, would be more concerned whether your light setup will provide enough light at that speed.

You'll be fine.

You don't know the hubs as well as Shimano's engineers do. No reason to doubt them.

I don't know about the rotational speed... But I have built my own dynamo-powered led light. The dynamos self-limit to a specific current around 500ma, which is absolutely perfect for the recent led releases. As for the rpm's, though... I don't go that fast! Maybe 30mph once or twice, but I'm on 700c wheels. If you're worried about excess voltage, you could add in a zener diode.

From my own experience: My hub is the Sturmey Archer drum brake/dynamo hub (I hear SA and Shimano both use the same Sanyo internals... Haven't verified that.) I have two Cree Q2 led's in series with nothing else but a bridge rectifier. It's always on. I've tried on vs off, and I can't feel any difference. So I tested by coasting, on vs off, on a hill on my commute route. Wet vs dry pavement has a far more significant effect than having the light on or off! And people really notice the lights, so I leave them on. You may have seen them at some time - I do live in Vancouver; we've crossed paths once or twice. But I don't think officially since I've added the dynamo lights. If you see a long haul trucker with two led lights on the front of a removable basket with a coroplast lid on it, that's me.

I know that the hub itself generates some drag whether you're using the power or not, it's obvious from turning the axle. It feels just like notchy cup and cone bearings. Maybe the drag from the magnetic field interaction wouldn't increase with speed like it would with mechanical friction from bad bearings. There's a "push" and a "pull" on each side of the magnetic "notch", unlike notchy bearings, and no mechanical impact. So it seems like the notchy-bearings concept might be the most conservative way to describe the drag. Kind of a worst case scenario. Probably not that much, but it's there. It's probably measurable in time trials if you're a consistent rider.

You'll be fine.

You don't know the hubs as well as Shimano's engineers do. No reason to doubt them.

Well... I don't doubt them. I've dealt with Shimano stuff for 30 years and they rarely put out a poorly engineered product. (Some of the decisions that led to that product being produced, though...)

However, I'm going to be travelling quite fast with a smaller than conventional wheel. As I said, it'll be the equivalent of a 700C wheel at 50 miles per hour. I guess I get to be a guinea pig for this... which is better than being a ninja.

And people really notice the lights, so I leave them on. You may have seen them at some time - I do live in Vancouver; we've crossed paths once or twice.

Uhhhh... which Vancouver? I live in the United State-ian Vancouver, the suburb of Portland, Oregon. My commute takes me across the Columbia River on the I-205 bridge in the morning. I see a number of riders going both directions, even though I'm usually driving to work at about 6AM.

Uhhhh... which Vancouver? I live in the United State-ian Vancouver, the suburb of Portland, Oregon. My commute takes me across the Columbia River on the I-205 bridge in the morning. I see a number of riders going both directions, even though I'm usually driving to work at about 6AM.

That's America's Vancouver, according to Uncle Royce! :D I'm a westside resident, but I've been known to turn up at a two-bridge-loop or two, or hpv events.

That's America's Vancouver, according to Uncle Royce! :D I'm a westside resident, but I've been known to turn up at a two-bridge-loop or two, or hpv events.

Okley-dokley! BTW: I'll be riding to the Handmade Bike Show Sunday with my wife, and then I'm scheduled to do some bike path maintenance on the 7th:
http://www.google.com/calendar/event?eid=b3JmcmM2ZmhmMjZrMDk2MnFmdW9zcHNpYWMgdmJjcm9hZGNhcHRhaW5AbQ&ctz=America/Los_Angeles

It's probably measurable in time trials if you're a consistent rider.

Me, consistent? Bwah-hah-ha! :roflmao2:

I chatted for quite a while with the Light On LED guy at the Handmade Bike Show this afternoon, and his answer went thus: "I dunno". I guess I get to put it all together and find out what blows up.

The Constructors Challenge bikes were facinating. Lots and lots of the entries had Schmidt dynohubs and LED headlights. I guess it's the wave of the future!

I did notice that several of the hubs were marked as for 16-20" wheels and were laced to 700C or 650B wheels. Any guesses why? Lower resistance? Peter White out of stock of normal hubs?

I chatted for quite a while with the Light On LED guy ...

Light On -
Apply directly to the forehead!

http://www.youtube.com/watch?v=Is3icfcbmbs

It just occurred to me... ;)

I did notice that several of the hubs were marked as for 16-20" wheels and were laced to 700C or 650B wheels. Any guesses why? Lower resistance? Peter White out of stock of normal hubs?the 20" wheel hubs are lighter, have lower resistance, and work fine with a 700c and LED lights. The only downside is that the flange spacing is narrower.