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Adam Lea[_2_] August 5th 09 12:10 AM

hub dynamo question
 
I am toying with the idea of getting a hub dynamo for the coming winter,
however the wheels on my road bike only have 20 spokes which is less than
more conventional wheels which I understand have 32 or 36 spokes. Are there
any hub dynamos that would be compatible with my wheels?

Also, how easy would it be to install the dynamo myself, given that the
spokes go straight out from the hub to the rim? It looks as though it should
be easier than rebuilding a conventional wheel but there may be something I
have missed (I have never tried wheelbuilding before).

Adam



Clive George August 5th 09 12:21 AM

hub dynamo question
 
"Adam Lea" wrote in message
...
I am toying with the idea of getting a hub dynamo for the coming winter,
however the wheels on my road bike only have 20 spokes which is less than
more conventional wheels which I understand have 32 or 36 spokes. Are
there any hub dynamos that would be compatible with my wheels?

Also, how easy would it be to install the dynamo myself, given that the
spokes go straight out from the hub to the rim? It looks as though it
should be easier than rebuilding a conventional wheel but there may be
something I have missed (I have never tried wheelbuilding before).


The tricky bit of wheelbuilding is getting all your spoke tensions right,
and this applies on both your current 20 straight-pull spoke one and a more
conventional setup. So you won't lose anything by going to a traditional
wheel style.

I reckon you'd be better off getting a new rim as well. You'll need
different spoke lengths anyway.

That way you end up with a light wheel for going fast, and a dynamo wheel
for the rest of the time. You've also got a spare in case of problems.

cheers,
clive



Craig Wallace August 5th 09 01:58 AM

hub dynamo question
 
On 05/08/2009 00:10, Adam Lea wrote:
I am toying with the idea of getting a hub dynamo for the coming winter,
however the wheels on my road bike only have 20 spokes which is less than
more conventional wheels which I understand have 32 or 36 spokes. Are there
any hub dynamos that would be compatible with my wheels?

Also, how easy would it be to install the dynamo myself, given that the
spokes go straight out from the hub to the rim? It looks as though it should
be easier than rebuilding a conventional wheel but there may be something I
have missed (I have never tried wheelbuilding before).


The SON 20R is available in a 20 spoke version. Its designed for 20"
wheels - it will still work in a 700C wheel, but will generate less
power (and have less drag).
Though its not cheap.

Shimano used to make a 20 spoke wheel with dynamo hub, though I don't
think that version of the hub was available on its own. (I've got one,
though I've since replaced the rim).

I'd agree with Clive that if getting a dynamo hub, you might as well get
a whole new wheel. Unless your rim is particularly expensive, it won't
cost that much more. Plus you'll have a spare wheel.
A few of the German webshops have dynamo wheels for reasonable prices,
eg Roseversand.de

--
Craig Wallace
http://craig.neogeo.org.uk
http://www.neogeo.org.uk

Rob Morley August 5th 09 06:22 AM

hub dynamo question
 
On Wed, 5 Aug 2009 00:10:54 +0100
"Adam Lea" wrote:

I am toying with the idea of getting a hub dynamo for the coming
winter, however the wheels on my road bike only have 20 spokes which
is less than more conventional wheels which I understand have 32 or
36 spokes. Are there any hub dynamos that would be compatible with my
wheels?

Don't bother trying to rebuild your existing wheel - just buy a
complete conventional wheel with a dynamo hub, or buy the bits and build
it yourself. That gives you the choice of good illumination at the
cost of weight and drag, or lower weight and lower drag, quickly and
easily interchangeable.


Simon Brooke[_2_] August 5th 09 08:33 AM

hub dynamo question
 
On 5 Aug, 00:10, "Adam Lea" wrote:
I am toying with the idea of getting a hub dynamo for the coming winter,
however the wheels on my road bike only have 20 spokes which is less than
more conventional wheels which I understand have 32 or 36 spokes. Are there
any hub dynamos that would be compatible with my wheels?

Also, how easy would it be to install the dynamo myself, given that the
spokes go straight out from the hub to the rim? It looks as though it should
be easier than rebuilding a conventional wheel but there may be something I
have missed (I have never tried wheelbuilding before).


Radial spoking cannot be used to transmit torque from the hub to the
rim - which is why you never see it on rear wheels or dick braked
wheels. The torque required for a hub dynamo is much smaller of
course, but radial spoking is still not recommended. You need to go at
least one cross; having seen Ian's analysis of spoking, I'm not
convinced you need to go two cross.

I too am planning to build myself a dynohub wheel for this winter,
probably using a SON S20R (Yes, I know it's three times the price of a
perfectly good Shimano part). I'll be lacing two cross on a DTSwiss
R1.1 rim. I already have a pair of home made wheels with Record hubs
and DTSwiss R1.1 rims, so this will be the winter/expedition front for
that wheelset. There's nothing specially difficult in lacing wheels
anyway - all it takes is care and patience - and the dynohub, being
relatively large, should be easier than a smaller hub.

The SON 20 series are designed for twenty inch wheels which rotate
more frequently at a given speed - so to produce the same power
output, in a 700C wheel, you have to ride faster. But they're designed
(in accordance with German law) to produce full brightness with a
halogen bulb at 7Km/h - about 4 mph. New LED lamp heads are much more
efficient, so will work well with a '20" wheel hub' in a 700C; and in
any case, when did you last ride any distance at 7Km/h?

What I'm saying, in essence, is keep your existing front as a summer
wheel, and build yourself a whole new wheel.

Just zis Guy, you know?[_2_] August 5th 09 09:39 AM

hub dynamo question
 
On Wed, 5 Aug 2009 00:21:56 +0100, "Clive George"
wrote:

I reckon you'd be better off getting a new rim as well. You'll need
different spoke lengths anyway.
That way you end up with a light wheel for going fast, and a dynamo wheel
for the rest of the time. You've also got a spare in case of problems.


I think that is the smart solution, given that only the rim would be
reused in the alternative scenario.

Guy
--
http://www.chapmancentral.co.uk/urc | http://www.nohelmetlaw.org.uk/
"Nullius in Verba" - take no man's word for it.
- attr. Horace, chosen by John Evelyn for the Royal Society

_[_2_] August 5th 09 11:39 AM

hub dynamo question
 
On Wed, 5 Aug 2009 00:33:14 -0700 (PDT), Simon Brooke wrote:

Radial spoking cannot be used to transmit torque from the hub to the
rim - which is why you never see it on rear wheels or dick braked
wheels.


Not strictly true, assuming you mean the common definition of radial
spoking. The out is that wheels which at rest are spoked radially, have
hubs and spokes which, when torque is applied, "wind up"; which changes
them from radial to being at a very slight angle, and then then transmit
torque through tension, as do wheels spoked in more tangential patterns.

It's not that wheels spoked in this manner cannot transmit torque; it is
rather that to relaibly use ant common hub in this fashion risks flange
breakage.

_[_2_] August 5th 09 11:45 AM

hub dynamo question
 
On Wed, 05 Aug 2009 10:39:03 GMT, _ wrote:

On Wed, 5 Aug 2009 00:33:14 -0700 (PDT), Simon Brooke wrote:

Radial spoking cannot be used to transmit torque from the hub to the
rim - which is why you never see it on rear wheels or dick braked
wheels.


Not strictly true, assuming you mean the common definition of radial
spoking. The out is that wheels which at rest are spoked radially, have
hubs and spokes which, when torque is applied, "wind up"; which changes
them from radial to being at a very slight angle, and then then transmit
torque through tension, as do wheels spoked in more tangential patterns.

It's not that wheels spoked in this manner cannot transmit torque; it is
rather that to relaibly use ant common hub in this fashion risks flange
breakage.


Godnesss; usualy I proffread more karefuly then that:

"...reliably use any..."

Clive George August 5th 09 11:58 AM

hub dynamo question
 
"Simon Brooke" wrote in message
...

Radial spoking cannot be used to transmit torque from the hub to the
rim - which is why you never see it on rear wheels or dick braked
wheels. The torque required for a hub dynamo is much smaller of
course, but radial spoking is still not recommended. You need to go at
least one cross; having seen Ian's analysis of spoking, I'm not
convinced you need to go two cross.


The front wheel on my wife's birdy is close to radial and has a dynohub - no
obvious problems. (close to radial - it's a 36H hub and a 24H rim, so every
third hole on the hub is missed which means theres an ever-so-slight angle
to the spoke).



Mark McNeill August 5th 09 12:12 PM

hub dynamo question
 
Response to _:

On Wed, 5 Aug 2009 00:33:14 -0700 (PDT), Simon Brooke wrote:

Radial spoking cannot be used to transmit torque from the hub to
the rim - which is why you never see it on rear wheels or dick
braked wheels.


Not strictly true, assuming you mean the common definition of radial
spoking. The out is that wheels which at rest are spoked radially,
have hubs and spokes which, when torque is applied, "wind up";
which changes them from radial to being at a very slight angle, and
then then transmit torque through tension, as do wheels spoked in
more tangential patterns.

It's not that wheels spoked in this manner cannot transmit torque;
it is rather that to relaibly use ant common hub in this fashion
risks flange breakage.


Godnesss; usualy I proffread more karefuly then that:

"...reliably use any..."


I have to say, it was actually Simon's unusual braking system that I was
worried about.


--
Mark, UK.



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