#1
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Dynohub drag
I just completed my Edelux II setup. To give Jay piece of mind (or not)
about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. -- Lou |
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#2
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Dynohub drag
On Tuesday, October 7, 2014 11:50:50 AM UTC-7, Lou Holtman wrote:
I just completed my Edelux II setup. To give Jay piece of mind (or not) about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. I don't know if my Shutter Precision PD-8 runs that freely. Spinning it in my truing stand, it slowed down pretty fast -- but I'll clamp the complete wheel/tire in the forks when I get home and give it a good spin and see what it does. I'll also have to find some throbbing rock-n-roll music to get me all psyched up for the test. -- Jay Beattie. |
#3
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Dynohub drag
On 10/7/2014 2:50 PM, Lou Holtman wrote:
I just completed my Edelux II setup. To give Jay piece of mind (or not) about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. Impressive! It looks like roughly 45 seconds light off, 20 seconds light on. That's a SON hub, correct? I tried it with my Shimano DH-3N30 and Cyo headlight. I got about 20 seconds light off, about 10 seconds light on. I assume my wheels are significantly heavier than yours, too, which should increase my spin-down time. But there's no way to tell how close we were on the initial speed. I'll note that the drag from the Shimano hub is not noticeable while riding. It would matter only in competition. -- - Frank Krygowski |
#4
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Dynohub drag
On 08/10/14 05:59, jbeattie wrote:
On Tuesday, October 7, 2014 11:50:50 AM UTC-7, Lou Holtman wrote: I just completed my Edelux II setup. To give Jay piece of mind (or not) about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. I don't know if my Shutter Precision PD-8 runs that freely. Spinning it in my truing stand, it slowed down pretty fast -- but I'll clamp the complete wheel/tire in the forks when I get home and give it a good spin and see what it does. I'll also have to find some throbbing rock-n-roll music to get me all psyched up for the test. Pretty sure my SP PV-8 with BUMM light would be quite comparable to Lou's set up. -- JS |
#5
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Dynohub drag
On Tuesday, October 7, 2014 9:50:26 PM UTC+2, Frank Krygowski wrote:
On 10/7/2014 2:50 PM, Lou Holtman wrote: I just completed my Edelux II setup. To give Jay piece of mind (or not) about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. Impressive! It looks like roughly 45 seconds light off, 20 seconds light on. That's a SON hub, correct? That is right: a SONdelux. I tried it with my Shimano DH-3N30 and Cyo headlight. I got about 20 seconds light off, about 10 seconds light on. I assume my wheels are significantly heavier than yours, too, which should increase my spin-down time. But there's no way to tell how close we were on the initial speed. It was a rough test of course. I gave it just a firm spin as you can see in the movie. Nothing special. It was just to show people that the drag with the lights off is so low that you don't need the complexity of a disengagement mechanism. I'll note that the drag from the Shimano hub is not noticeable while riding. It would matter only in competition. That is what I hear from everybody with a hub dynamo. In competition? Very few races in the dark. I'm a nutcase who just choose the best at the moment of decision. Reliabity, low weight, low drag; I don't want to pick just two out of three to make it cheap if it is possible. I'm willing to pay about 150 euro extra for that. That is insignificant over the lifetime of the hub. However you are right that you get a very, very decent hub dynamo (Shimano XT, Ultegra level) for about 70 euro here. Lou |
#6
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Dynohub drag
On 10/8/2014 12:39 AM, Lou Holtman wrote:
It was just to show people that the drag with the lights off is so low that you don't need the complexity of a disengagement mechanism. The reality is that you did show that at all. You showed the difference between spin down time with and without the light on. You did not show the drag from an unconnected engaged hub versus an unconnected disengaged hub versus a non-dynamo hub. It was still instructive. It was surprising how much more drag their was with the light on in your test. I would have expected far less difference in spin-down time. A 50% efficient hub that is generating 3W requires 6W of input. Someone riding a bicycle at 15 km/hour is expending about 60W of power (I recall 1/10 HP which would be about 75W, though this is a little less). So it's an extra 10% input power with the light on versus off. Not huge, but not insignificant. A test of the SP clutch hub showed the following: O:17 Hub-engaged light-on 0:33 Hub-engaged light-off 2:53 Hub-disengaged https://www.youtube.com/watch?v=ji1wCW35Y0o But of course all these tests, yours and the one of the SP hub, are pretty meaningless. Spinning a wheel with your hand is not representative of actual riding. Also, there are other reasons for a disengageable hub besides less drag. |
#7
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Dynohub drag
On 10/8/2014 5:49 AM, sms wrote:
On 10/8/2014 12:39 AM, Lou Holtman wrote: It was just to show people that the drag with the lights off is so low that you don't need the complexity of a disengagement mechanism. The reality is that you did show that at all. You showed the difference between spin down time with and without the light on. You did not show the drag from an unconnected engaged hub versus an unconnected disengaged hub versus a non-dynamo hub. That data is available; see below. Lou was just giving an easy-to-understand demonstration, to make obvious how little problem there is with the drag. Juden's article does the same in a quantitative way. It was still instructive. It was surprising how much more drag their was with the light on in your test. I would have expected far less difference in spin-down time. A 50% efficient hub that is generating 3W requires 6W of input. Someone riding a bicycle at 15 km/hour is expending about 60W of power (I recall 1/10 HP which would be about 75W, though this is a little less). So it's an extra 10% input power with the light on versus off. Not huge, but not insignificant. A test of the SP clutch hub showed the following: O:17 Hub-engaged light-on 0:33 Hub-engaged light-off 2:53 Hub-disengaged https://www.youtube.com/watch?v=ji1wCW35Y0o But of course all these tests, yours and the one of the SP hub, are pretty meaningless. Spinning a wheel with your hand is not representative of actual riding. Also, there are other reasons for a disengageable hub besides less drag. Hmm... perhaps another reason is to increase complexity? There is detailed, yet easy to understand, data on the drag of these and other hub dynamos at http://www.ctc.org.uk/file/public/fe...ub-dynamos.pdf The first graph in that article shows slightly more drag for the SP than for the SON, although the difference is only about 0.4W at 30 kph. SP's own graphs at http://www.sp-dynamo.com/8seriesdynamo%20hub.html show differences of about the same magnitude, but in the opposite direction. Perhaps they were comparing with a different model of SON hub? In any case, a fraction of a Watt is hardly important. Juden's article makes that very clear, by converting drag to equivalent feet-per-mile inclines. I own neither of those hubs, so I don't particularly care. Seems to me the criteria for choosing between the two might be lower cost for the SP, vs. perhaps greater reliability for the SON (based on greater simplicity and SON's unique sealing technology). -- - Frank Krygowski |
#8
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Dynohub drag
sms writes:
On 10/8/2014 12:39 AM, Lou Holtman wrote: It was just to show people that the drag with the lights off is so low that you don't need the complexity of a disengagement mechanism. The reality is that you did show that at all. You showed the difference between spin down time with and without the light on. You did not show the drag from an unconnected engaged hub versus an unconnected disengaged hub versus a non-dynamo hub. It was still instructive. It was surprising how much more drag their was with the light on in your test. I would have expected far less difference in spin-down time. A 50% efficient hub that is generating 3W requires 6W of input. Someone riding a bicycle at 15 km/hour is expending about 60W of power (I recall 1/10 HP which would be about 75W, though this is a little less). So it's an extra 10% input power with the light on versus off. Not huge, but not insignificant. If I'm riding at 15 km/hr, the grade is going to be about 8% and, even at my weight, will be putting out a bit more than 60W. "Extra 10%" is a ridiculous figure when you are talking about puttering around on the bike. -- Joe Riel |
#9
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Dynohub drag
On 10/8/2014 8:27 AM, Joe Riel wrote:
snip If I'm riding at 15 km/hr, the grade is going to be about 8% and, even at my weight, will be putting out a bit more than 60W. "Extra 10%" is a ridiculous figure when you are talking about puttering around on the bike. Personally I don't care about putting out an extra few watts. But some people try to eliminate all unnecessary drag. There is a measurable difference between the three scenarios as Lou and the other tester demonstrated. It's interesting that in the U.S., GM who was big proponent of daytime running lights (DRLs), applied for, and was granted, permission to disconnect the DRLs for government fuel economy tests (so all, if there were any other, manufacturers with DRLs that could not be turned off got the same permission). Since DRLs are not mandatory in the U.S. GM felt that they should not be penalized for including them. I find it difficult to believe that an extra 35-50W load on the alternator would cause a measurable difference in fuel economy which is advertised in whole numbers, but GM felt that it could. I guess if you're at 34.499 MPG versus 34.501 MPG you have to round up or down accordingly, and they were not taking any chances that they'd run into that unlikely scenario. The claim was that their could be a 0.25 MPG difference due to the DRLs. The EPA letter is he http://web.archive.org/web/20080516061438/http://www.epa.gov/otaq/cert/dearmfr/cd9402.pdf The EPA may have withdrawn this exception since this was issued. But it may not have been necessary since most new cars can now turn off the DRLs. Not sure about vehicles sold in Canada where DRLs are mandatory. |
#10
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Dynohub drag
On Wednesday, October 8, 2014 8:39:25 AM UTC+1, Lou Holtman wrote:
On Tuesday, October 7, 2014 9:50:26 PM UTC+2, Frank Krygowski wrote: On 10/7/2014 2:50 PM, Lou Holtman wrote: I just completed my Edelux II setup. To give Jay piece of mind (or not) about the drag I spinned the dynohub wheel (SON edelux) with and without the headlight on. Made a small film about it. Can be downloaded (45 MB) for 7 days by clicking on this link: http://we.tl/RunDtdGcnx You can trust this site and me, or not of course. Impressive! It looks like roughly 45 seconds light off, 20 seconds light on. That's a SON hub, correct? That is right: a SONdelux. I tried it with my Shimano DH-3N30 and Cyo headlight. I got about 20 seconds light off, about 10 seconds light on. I assume my wheels are significantly heavier than yours, too, which should increase my spin-down time. But there's no way to tell how close we were on the initial speed. It was a rough test of course. I gave it just a firm spin as you can see in the movie. Nothing special. It was just to show people that the drag with the lights off is so low that you don't need the complexity of a disengagement mechanism. I'll note that the drag from the Shimano hub is not noticeable while riding. It would matter only in competition. That is what I hear from everybody with a hub dynamo. In competition? Very few races in the dark. I'm a nutcase who just choose the best at the moment of decision. Reliabity, low weight, low drag; I don't want to pick just two out of three to make it cheap if it is possible. I'm willing to pay about 150 euro extra for that. That is insignificant over the lifetime of the hub. However you are right that you get a very, very decent hub dynamo (Shimano XT, Ultegra level) for about 70 euro here. Lou I've always quantified the difference as like a foot of road tilt in every mile, an imperceptible difference. Andre Jute |
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