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

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.

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

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

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

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.

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

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

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.

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