Switchable Dyno Hub

[Allan in Portland]

While waiting for the latest BQ to "drop", I thought I'd prime the
pump (and give Philip company) with this post.

The much (skeptically?) anticipated switchable dynohub from VO
recently became available. The hullabaloo concerns a clutch which
allows the wheel to spin with no additional drag when the dyno is off.

Certain engineers and scientists have expressed skepticism that a
clutch is necessary as the drag from an unloaded dyno is essentially
negligible compared to all the other drags a bicycle with rider moving
through space experiences.

Well, I, for one, have redoubled my skepticism. I don't want to go so
far as to suggest they don't "get it", I'll allow that their
engineering dept is not on the best of terms with their marketing
dept, but the following copy from the manufacturer's web site is
suspicious, if not suggestive.

from: http://www.sp-dynamo.com/spproductswitchdisc.html
"With advanced switch devise[sic], magnet drag is removed i.e. there
is totally no magnet drag in power off mode. Therefore, it is the
world's smoothest dynamo hub."

Actually, it's funny how they helpfully redefine smooth in a
theoretical sense so as to lay unequivocal claim being the world's
smoothest.

Of course we BQ readers know from Jan's Winter 2010 review of the
Shimano hub that smoothness with the dyno ON is more important the
*drag* with the dyno OFF, at least for rando/touring distances.
Curious how they make no mention of the dyno ON performance.

I'll allow it theoretically possible this hub resets the standard in
dyno hubs and send the Germans scurrying back to their slide rules and
SPICE models, but based on their web site and the amount of effort the
spent solving a problem most technically inclined people think doesn't
exist, smart money says no.

To spur discussion, I'll leave a critique of their "Test Summary"/
video demo as a challenge/exercise for the crowd.

Regards,
-Allan

[msrw]

Allen, you raise an interesting issue--is dynohub drag in the case of
a high performance dynohub like a Sondelux meaningful in any way?

As a data point, I was riding the other day with a bunch of "A" group
cyclists in Santa Fe--all of whom were on carbon road racing bikes.
The majority were using Mavic Kysrium SSC wheels, (low spoke count,
lightweight, fast wheels) with 700x23 or 700x25 racing tires. I was
riding a rando bike with 32/36 spoke traditional wheels with a
Sundelux dynohub and Marathon Supreme 700x32 high performance touring
tires. About half the riders were around my size and weight--riding
was aggressive.

There are any number of variables here, but what surprised me is that
on major downhill sections of the ride where we were all coasting at
between 25 and 35 mph, my rando bike with the dynohub and high spoke
count wheels coasted SIGNIFICANTLY faster than ANY of the other
bikes.

I would think that higher spoke count wheels, less supple tires and
the dynohub might have negatively impacted my relative coasting speed
compared to that of everyone else, while the wider tires would might
positively impacted my relative coasting speed. If so, it would seem
that tire width may be a much more significant factor than spoke
count, tire suppleness and dynohub drag--tire width appeared, in this
case at least, to trump the other variables.

One anecdote doesn't necessarily support a general conclusion; but in
this one circumstance, there was no negative impact whatsoever on
coasting speed with a Sondelux dynohub even when compared to the
performance of bikes with top of the line aero racing wheels. So the
added complexity of a dynohub with a clutch mechanism would appear to
be a solution in search of a problem. For me, the most simple
possible solution to a need usually tends also to be the most reliable
solution. On this basis, it seems superfluous in the extreme to go
with a dynohub with a clutch.

[Steve Palincsar]

On Tue, 2011-04-05 at 08:58 -0700, msrw wrote:
>
> There are any number of variables here, but what surprised me is that
> on major downhill sections of the ride where we were all coasting at
> between 25 and 35 mph, my rando bike with the dynohub and high spoke
> count wheels coasted SIGNIFICANTLY faster than ANY of the other
> bikes.
>
> I would think that higher spoke count wheels, less supple tires and
> the dynohub might have negatively impacted my relative coasting speed
> compared to that of everyone else, while the wider tires would might
> positively impacted my relative coasting speed. If so, it would seem
> that tire width may be a much more significant factor than spoke
> count, tire suppleness and dynohub drag--tire width appeared, in this
> case at least, to trump the other variables.

Or, maybe it was the Power of all that Road Hugging Weight...?

;-)

[msrw]

On Apr 5, 10:23 am, Steve Palincsar <palin...@his.com> wrote:
> Or, maybe it was the Power of all that Road Hugging Weight...?

Maybe--thanks for mentioning this. Of course it's another key
variable.

My rando bike is maybe 7-8 lbs heavier than a road racing bike; but
that relatively small difference in bike weight would have been offset
by the varying weight of the riders--on that particular ride I
definitely wasn't the heaviest rider. There were a handful of riders
that exceeded my weight by more than the differences in our bike
weights. So I don't think I was the heaviest in combined bike/rider
weight, and yet still was out-coasting the whole peleton.

[Ryan Watson]

I have a SON 20R and don't notice any drag when riding, whether the lights are on or off.
I also have a Shimano dyno, who's drag is very noticeable (at least to me).
I see the switchable hub as an alternative to the Shimano (and other less expensive hubs) not the Schmidt. My plan is to use the switchable hub for the majority of my riding (which is almost never in the dark) and save the SON for special events (longer brevets and other night rides).
You may be right about the added complexity of the clutch, though: my new VO dyno failed on the first ride. The clutch mechanism isn't letting the dynamo engage properly. They're sending me a replacement, so I'm keeping my fingers crossed that the first one was a fluke.

Cheers,
Ryan

[Allan in Portland]

> I have a SON 20R and don't notice any drag when riding, whether the lights are on or off.

Exactly. I have _never_ felt an impulse turning my light on or off.
What about a cumulative drag? I dunno... recently with the days longer
there has been a time or two where I thought to myself, hey I feel a
little faster today. Is it having the light off? Or the sun up?

> I also have a Shimano dyno, who's drag is very noticeable (at least to me).

Interesting.

> You may be right about the added complexity of the clutch, though: my new VO dyno failed on the first ride. The clutch mechanism isn't letting the dynamo engage properly. They're sending me a replacement, so I'm keeping my fingers crossed that the first one was a fluke.

Whoops.

BTW, I just checked their web site, and the side-by-side comparisons
which I challenged folks to critique are gone. Well, I guess I'll go
ahead and give one critique, of many. Any experiment has a control,
their control was their own hub.

>
> Cheers,
> Ryan

Regards,
-Allan