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Old 11-29-07, 07:31 PM   #1
B17
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Dynohubs- how much friction do they generate?

I'm interested in a 2007 Castro Valley which comes with a Shimano Dynohub for the light. I will most likely not be using the light at all, as this will become my all-rounder rather than a purpose-built commuter. It will be used on and off-road, and possibly for some CX (I have drops, road levers, secondary levers, Shimano 9sp bar-cons and Paul Thumbies ready if I pull the trigger), which is where this question begins.

How much speed do these hubs scrub off as a rule? How heavy are they compared to conventional hubs of roughly the same quality? I'd likely be using almost everything currently on the bike except the cockpit stuff, and don't really want to invest in a second front wheel. Can this wheel be used at all for CX/offroad, or is it too heavy (or too friction-y) for anything but touring/commuting, where the necessity of a light would take priority over speed? Posting here instead of the CX forum because I figure you guys know more about dynohubs than the CX guys do, and here instead of the Touring forum because this bike really isn't a touring bike, what with the flat bar and all.

Thanks!
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Old 11-29-07, 07:49 PM   #2
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1) No noticeable reduction in speed.

2) They are heavier, maybe a pound or so. I don't know for sure, because I had the shop build mine into a wheel before shipping it to me.

3) They are nice units. You hop on the bike and go, and the light comes silently on.

4) If I wanted a bike without lights (which for me would be like wanting a car with no lights), I don't know why I would buy a bike with a dynohub.

If you want to do CX, why not buy a CX bike? Lots of people commute on them.

Paul
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Old 11-29-07, 07:52 PM   #3
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I'm interested in a 2007 Castro Valley which comes with a Shimano Dynohub for the light. I will most likely not be using the light at all, as this will become my all-rounder rather than a purpose-built commuter. It will be used on and off-road, and possibly for some CX (I have drops, road levers, secondary levers, Shimano 9sp bar-cons and Paul Thumbies ready if I pull the trigger), which is where this question begins.

How much speed do these hubs scrub off as a rule? How heavy are they compared to conventional hubs of roughly the same quality? I'd likely be using almost everything currently on the bike except the cockpit stuff, and don't really want to invest in a second front wheel. Can this wheel be used at all for CX/offroad, or is it too heavy (or too friction-y) for anything but touring/commuting, where the necessity of a light would take priority over speed? Posting here instead of the CX forum because I figure you guys know more about dynohubs than the CX guys do, and here instead of the Touring forum because this bike really isn't a touring bike, what with the flat bar and all.

Thanks!
Just replace the front wheel and ship the one that comes with the bike to me!

That would take care of that problem, wouldn't it?
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Old 11-29-07, 08:12 PM   #4
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1) No noticeable reduction in speed.
None? At all? Good to know.

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2) They are heavier, maybe a pound or so. I don't know for sure, because I had the shop build mine into a wheel before shipping it to me.
A pound over the standard hub... I'm now officially concerned.

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4) If I wanted a bike without lights (which for me would be like wanting a car with no lights), I don't know why I would buy a bike with a dynohub.
Well, it has all the things I'd want in an all-rounder- it's steel, takes cantis, is CX-able, and because of the slight TT slope, can be set up for a comfortable riding position without looking silly. The hub is the only thing I don't already have the parts to replace.

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If you want to do CX, why not buy a CX bike? Lots of people commute on them.

Paul
42.5cm chainstays, cantis, cable guides atop the TT rather than underneath, indention for your shoulder, you get the pic- it's a CX frame with flat bars and some commuter parts, not a true touring/commuting frame. And sadly, most CX bikes these days are either aluminum (no sir, no how, no way) or waaay more expensive than this one.

I'd be thinking about the Volpe (same frame), but the price on this one is too hard to pass up- IF the wheel is CXable. I just flipped a Soma Double Cross frame because it was going to be too long in the top tube at 56cm or too much post and "quill" at 54cm. The Surly Cross-Check has an ugly fork (I love lugs, but the blades have a bend rather than a gentle curve, which is a dealbreaker).

Why can't Bikes Direct make a steel CX bike?
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Old 11-29-07, 08:14 PM   #5
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Just replace the front wheel and ship the one that comes with the bike to me!

That would take care of that problem, wouldn't it?
Well, yes, I suppose it would. But I'm hoping it doesn't come to that.
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Old 11-29-07, 08:15 PM   #6
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I have a Shimano dynohub and a SON dynohub. They both noticeably affect the performance of your bike - the Shimano more than the SON as I have it built up into a small 406 wheel. It isn't a huge problem, but you'll know you don't have a standard hub on your bike.

Bicycle Quarterly did a test on how much drag they introduce at different speeds.



Bicycle Quarterly is an awesome magazine BTW - they only bike mag I read any more.
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Old 12-03-07, 10:19 AM   #7
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I don't think my Shimano dynamo hub adds noticeable friction (esp when it's a fairly burly commuter bike with fat tires) - but I do think it's a bit slower because of the added weight, if you see what I mean.
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Old 12-03-07, 11:50 AM   #8
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How much speed do these hubs scrub off as a rule?

I had a Shimano Hub wheel built for my by Peter White and as warned, when you move the wheel without a tire on it you can realy feel the "notches" caused by the magnets inside. Once the tire was on the wheel there was now a little mass on the outside of the wheel and this became almost not noticable. The funny thing is that the Shimano hubbed wheel is SMOOTHER running than my stock Bontranger wheel.

How heavy are they compared to conventional hubs of roughly the same quality?

The Shimano hub certainly will weigh a bunch more than the stock hub, but the bearings were of higher quality (on my Garry Fischer Nirvanna)

I'd likely be using almost everything currently on the bike except the cockpit stuff, and don't really want to invest in a second front wheel. Can this wheel be used at all for CX/offroad, or is it too heavy (or too friction-y) for anything but touring/commuting, where the necessity of a light would take priority over speed?

If you are ever out and it gets dark, at least you will be able to see and be seen. Always good to be prepared. I can't see that running the hub with the lights out will make you much slower. If you race I'd imagine that you could measure it easily, but for general riding, I would find it hard to tell the difference. I found the friction so low, I just leave the light on all the time.

Happy riding,
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Old 12-03-07, 12:16 PM   #9
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I was just checking out dynohubs at the LBS last week. The Shimano 3N71 and the SON28 both feel about the same for the friction factor. When the lights are switched off, the friction is negligible. When the lights are switched on, there's a noticeable drag (when turning a wheel by hand) but when you put it on a bike you can barely tell the difference between the on and off resistances.

As for the weight of the hub, here's the tradeoff: An extra pound of hub that generates light whenever you want/need it, versus a one to 1 1/5 pound battery that will hold (on average) only 2 to 3 hours of charge if you remembered to plug it in. You can remove the battery powered lights easily if you don't need them, but you can't have them ready at a moment's notice like a dynohub.

If you're looking to CX with the bike, consider the durability and strength of the dynohub. It's meant for commuting, touring, and long-distance riding like brevets and rando's. Not beating the tar out of it in the mud and on gravel.
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Old 12-03-07, 03:17 PM   #10
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Having just recently had my front wheel rebuilt with a dynohub I can say I've noticed no difference in speed or resistance from it. The convenience of having the always ready light makes up for any additional weight, but I'm riding a '74 Speedster, so it wasn't exactly a flyweight to begin with...
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Old 12-03-07, 03:25 PM   #11
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I don't know that the hub on my Castro Valley comes into play that much. Certainly less effect than the fenders, but the 42T front ring definitely limits top speed. Though if you're spinning out at 27 mph on an XC course, that's probably pretty good, huh?
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Old 12-03-07, 03:33 PM   #12
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I have been running the SON w a 3w LED Supernova headlight. I am riding a SOMA Double Cross 1x9 (11-34) w/ a 42th chainring up front. It has no real effect on the speed IMHO because I am slow by serious enthusiatst standards (14mph av.). If you don't need the hub just swap in a new wheel and save the the original wheel with the hub. You never know when you may need it.

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Old 12-03-07, 03:39 PM   #13
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as far as I remember using the SON hub dynamo resulted in an approximate increase of work done equivalent to cycling up an extra 0.5m per 1km travelled- so the energy losses from running a SON are certainly nothing to worry about
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Old 12-03-07, 05:28 PM   #14
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as far as I remember using the SON hub dynamo resulted in an approximate increase of work done equivalent to cycling up an extra 0.5m per 1km travelled- so the energy losses from running a SON are certainly nothing to worry about
I've always seen it in Watts and never worked the maths to make it quantifiable in regular people units.

At 0.5m/Km, that's the equivalent of making the StP (Seattle to Portland, 208 miles) appoximately 166.5m longer... or about 1.75 football fields. Assuming a rough estimate of 3000 miles for RAAM, the race would feel 1.5 miles longer.

Makes me feel pretty good about my decision to get a SON28 built into my LHT over the new year. Although, with the number of times I've forgotten to charge my headlight, I'd have bought it anyway just for the convenience.
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Old 12-04-07, 03:11 AM   #15
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I've ridden double centuries with my SON hub. I've never noticed any drag.
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Old 12-04-07, 04:55 AM   #16
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Hi

I have a SON dynohub and it is the best investment I have made not having to worry about recharging batteries. Schmidt hubs are a little mopre expensive than the Shimano models but there are other differences that in my view swing the equation in the SON's favour.

Some stats from Peter Whites Website - Peter White is the american distributor and although my experience with him is not good his wife Linda is reportedly extremely good to deal with. Anyway the Stats: weight 1.5 pounds (compares favourably with batteries for lights with any sort of runtime); only needs a service every 50,000 km; with lights off is the equivalent of climbing 1 foot every mile ie virtually nothing; with lights on equivalent of climbing 5 foot every mile. The best though is lights when you need them for as long as you can pedal your bike. I find with 2 E6 lights I get full power at about 18 km/h about half that if I switch the secondary off and run with just the primary light.

In short I have found it to be a worthwhile investment to my daily commute.
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Old 12-11-07, 10:36 AM   #17
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At 0.5m/Km, that's the equivalent of making the StP (Seattle to Portland, 208 miles) appoximately 166.5m longer... or about 1.75 football fields. Assuming a rough estimate of 3000 miles for RAAM, the race would feel 1.5 miles longer.
Actually, the dynohubs affect performance more than their enthusiasts appreciate. The peformance drain is not a great amount, true, but it is significant. It's enough to make me prefer battery lights, anyway.

How so? It's easiest to see if we just calculate the reductions in speed of dynohubs directly, rather than talking about comparisons to inclines per mile, or feelings of drag. It takes only a moment or two at analyticcycling.com to calculate the effect of various wattage drains on speed.

The Schmidt hub is very efficient, and draws a bit more than five watts of power away to produce three watts of power for the light. Other hubs do less well than that.

Let's suppose, though, that we have a hub that draws five watts of power away from the rotation of the wheel. Suppose a 165 pound (75kg) rider with a decent road bike on fair roads, riding on level ground, putting out 150 watts. Without the generator hub, this rider would travel at 18.63 miles an hour. With a hub draining five watts to produce light, this same rider would travel 18.36 miles an hour.

That's slightly more than a quarter mile per hour speed difference. Or, to put it another way, the cyclist above with the hub would lose about fifty seconds per hour racing against himself without the hub. In Clifton's 208 mile race above, the cyclist with the hub would lose nine and-a-half minutes.

Admittedly, fifty seconds per hour is not a lot of time for a utility cyclist to lose. Nevertheless, suppose you were choosing between two wheel sets neither one of which had a generator hub. Suppose the wheel sets were the same price, but one of the wheel sets caused frictional losses equal to those of the generator hub specified above. Wouldn't you buy the other, lower-friction set? Wouldn't you buy the lower-friction set even if it cost significantly more money?

Another way to consider the issue is to notice that aerodynamic wheelsets that reduce drag by an amount equivalent to the five watt difference noted above are very expensive. And, again, some other generator hubs do less well than draining only five watts away.

Of course, you might say, commmuters don't spend a lot of money on things like aerodynamic wheels. We are willing to forego speed gains for gains in strength and reliability in wheels. So too, one might say, it is with dynohubs. It's a good bargain to trade the speed away for the reliability of generator lights, some of you will say.

All right. Just speaking for myself, though, battery lights are preferable. They don't slow you down to power themselves. They're much brighter, too. Battery lights are less convenient than generator lights, true, but in absolute terms it is not very inconvenient to deal with charging batteries.

In any case, to each his own. If you value the convenience enough for these speed losses, then you do. However, it is worth understanding the speed losses of dynohubs in direct terms, rather than by comparison to inclines or by a subjective feel of drag on the wheel.

All that said, there's a way in which the generators are more in keeping with the idea of the bicycle in the first place. They're a mostly elegant way to use a small amount of human power to do a practical job surprisingly well. The cost in speed, and the larger cost in brightness, move me toward compromising the purity of this vision.
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Old 12-11-07, 11:07 AM   #18
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At 18.63mph, the 208 mile ride is 11.16 hours of rolling time.
At 18.36mph, it's 11.33 hours. That's a 1.74% difference.

If you're racing, then it's a big deal. Even over the course of a 1200km rando, the difference between a SON28 dynohub and versus battery lights is less than 1 hour of rolling time. (235 pound rider, 25 pound bike, medium wide tires, 14mph average speed) http://www.kreuzotter.de/english/espeed.htm
The difference for the same rider carrying enough batteries to stay lit for the duration of the ride (2x long-life Li-on packs) is a generated need for 2 more Watts of power to maintain the same speed. Less than the dynohub by more than half, so still the hands-down winner in overall efficiency.

Dynos are really a matter of convenience vs. price. Is it more cost effective to have 'on-demand' lighting which costs rolling efficiency, or to spend $500 or more dollars on a long-life Li-on (9 hour battery) light system which requires a charging stop?
To the 24 hour racer with a support crew, the batteries are probably a better idea. Maybe even for the credit card tourer who's staying in a hotel and can charge up each night. To the randonneur, who might get a few 30 minute naps at the roadside on a bus bench, the prospect of charging batteries might be slim. To the utility riders and commuters, the convenience probably outweighs the efficiency losses.
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Old 12-11-07, 11:51 AM   #19
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None. It's drag, not friction.
Just being Mr. Physics here.

From the looks of some of those graphs above though, some of the hubs are pretty horrendous. Any dyno that's generating that much drag with no load attached should be pitched in the trash.
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Old 12-11-07, 01:10 PM   #20
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but in absolute terms it is not very inconvenient to deal with charging batteries.
The question I might ask is, do you spend 50 seconds fiddling with your batteries for every hour you spend commuting?

(Even if you do, it's perfectly valid to say that you are willing to deal with batteries to be able to have a 10W or light)

If you spend more than 50 seconds out of every hour spent commuting, on plugging in/unplugging your batteries with your charger or your bike-light wires... then perhaps time savings is not a justification for using a battery light.
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Old 12-11-07, 01:49 PM   #21
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The question I might ask is, do you spend 50 seconds fiddling with your batteries for every hour you spend commuting?

(Even if you do, it's perfectly valid to say that you are willing to deal with batteries to be able to have a 10W or light)

If you spend more than 50 seconds out of every hour spent commuting, on plugging in/unplugging your batteries with your charger or your bike-light wires... then perhaps time savings is not a justification for using a battery light.
I spend about 10 seconds a day with my battery powered light. Plug in the charger at night, plug in the lamp head before riding. It's easy, and no skin off my teeth to 'do the dance' every night and remember to plug in my lights. However, on those nights where I forget to plug it in... the next day I either can't ride to work (no juice) or have to cut the day short (enough juice for the ride in only) and work at home in the evening.
The wattage/lumens output isn't a concern for me. I don't use some expensive 24hr racer 1000 lumen HID system right now. I have a 13W L&M Solo. While the 2.4 - 3.0W bulbs used on dyno lamps are lower Wattage, they produce an amazing amount of light due to the reflector and the lens glass. Someone was heading toward me last week with a twin-lamp setup on their dynohub, and it looked like a motorcycle coming down the MUP. Those things are really bright and well focused.
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Old 12-11-07, 05:53 PM   #22
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What everyone else said about the drag - you'll notice it if you spin the wheel by hand with the light on, but not riding your bicycle. Sometimes I can feel the hub working as a barely perceptible vibration through my handlebars. Usually I don't notice a thing.

As for toughness, it doesn't have any moving parts to break off. I'd say that commuting, touring and long-distance riding are pretty tough on equipment. Unless you're hitting some serious bumps, it ought to survive your average CX course.
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Old 12-12-07, 03:34 AM   #23
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None. It's drag, not friction.
Just being Mr. Physics here.

From the looks of some of those graphs above though, some of the hubs are pretty horrendous. Any dyno that's generating that much drag with no load attached should be pitched in the trash.
You can get one of the Shimano cheapies for under $40. The SON costs 3 times that.

YGWYPF
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Old 12-12-07, 01:14 PM   #24
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The question I might ask is, do you spend 50 seconds fiddling with your batteries for every hour you spend commuting?
Nope. Once a week I unplug my battery before I walk in the house, and plug it into the charger on my way by, then do the opposite the next morning. Total expenditure of time about 45 seconds per week, which is about 8 hours of commuting (about 4 hours of light usage).

The real question is, how much time would I spend in the hospital after dropping my front wheel in a pothole I didn't see in the middle of the countryside miles from any house in the pitch black while I was running a 6 watt lamp instead of a 13 watt HID?
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Old 12-12-07, 01:29 PM   #25
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Quote:
Originally Posted by ItsJustMe View Post
The real question is, how much time would I spend in the hospital after dropping my front wheel in a pothole I didn't see in the middle of the countryside miles from any house in the pitch black while I was running a 6 watt lamp instead of a 13 watt HID?
Don't just compare Watts to Watts on halogen dynohub lighting vs. HID battery lights. The 6W of light from a twin lamp dyno setup throws an amazing amount of illumination because of the reflector and cover glass design.
While a 6W dyno setup is no match for a 13W HID, it certainly performs as well as my 13W L&M Solo.
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