Coker wheel rubbing on brakes

Howdy

I've just installed a pair of Magura HS-11 brakes with a brake booster
arch on my Coker. They work great on the downhills, but on the uphills
when I'm pouring on the torque there's a distinct rubbing sound coming
from the brake area on the right hand side on the uni. Its kind of
annoying and I'd like to fix it before I try to do an 80km ride on it [
www.cyclechallenge.org.nz ]. I'm not entirely certain that the noise is
in fact coming from the brakes, as I can't see the brakes while I'm
riding. But most likely that's what its from as that's the only thing
I've changed recently. Any help from experienced Coker brake
setter-uppers would be appreciated!

As far as I can see the Airfoil rim isn't wildly out of true, and
there's a good 3-4mm clearence between the pads and rim on both sides
the whole way round. It could possibly be the join of the rim hitting
the pad, but again it seems to be in the wrong place in the pedal stroke
and almost the join is pretty smooth. I can't replicate the noise by
lifting the uni off the ground and spinning the wheel - seems that large
pedalling forces are involved. I have noticed that there is a lot of
lateral movement in the wheel - I can flex the wheel by hand so that it
touches the brake pads on either side. This plus the torque would
suggest to me that the noise comes from the wheel moving to the side
when I pedal hard. In which case I wonder whether there's anything I can
do about it at all?

I've already tried moving the brake on the right hand side out as far
away from the rim as possible, and its in the furthest away possible
position now and it still rubs.

Aarrrg! What to do?@!?

Tony


--
TonyMelton - NZUNi

The first NZUNi Weekend - October 25-27, Wellington. More info at
'www.unicycle.co.nz' (http://www.unicycle.co.nz)

'My Photo Gallery' (http://gallery.unicyclist.com/albur10) has new
photos and has been generally re-arranged and spruced up. 9/9/03

------------------------------------------------------------------------
TonyMelton's Profile: http://www.unicyclist.com/profile/2118
View this thread: http://www.unicyclist.com/thread/28954

You have two options to choose from.
a You could:
- Send it to U-turn and get him to tension the spokes until it is
equal to the 'Strongest Coker wheel in the world'
(http://tinyurl.com/j6fg), hopefully preventing the wheel from flexing
while you torque. Check out the 'update' (http://tinyurl.com/dmoh) too
while you are at it.
- You could send it to me for Christmas, and it would solve all your
braking worries. No-brakes, no-squeeks. I'm sure I could get used to
it or just chop the damn brakes off.a


--
Rowan - •·.·´¯`·.·•
------------------------------------------------------------------------
Rowan's Profile: http://www.unicyclist.com/profile/3772
View this thread: http://www.unicyclist.com/thread/28954

Thanks, Rowan. Yes Tony, its essentially all about the tension,
although if you have a narrow hub that will contribute to the problem.
In addition, a stiffer frame couldn't help.


--
U-Turn - Small fish, big pond

Weep in the dojo... laugh in the battlefield.

'Strongest Coker Wheel in the World'
(http://www.unicyclist.com/gallery/albup39)

-- Dave Stockton
------------------------------------------------------------------------
U-Turn's Profile: http://www.unicyclist.com/profile/691
View this thread: http://www.unicyclist.com/thread/28954

OK, looks like I could try increasing the spoke tension. (The frame is a
custom made one with ovalised tubing so it should be reasonably stiff.
The hub is the standard Suzue, though.)

How did you get such massive tension on your Super Coker spokes, David?
Could I do it by hand with my spoke wrench or would I need special
tools? Could a bike shop apply sufficient tension to stop the flex?


Tony


No sig


--
TonyMelton - NZUNi

The first NZUNi Weekend - October 25-27, Wellington. More info at
'www.unicycle.co.nz' (http://www.unicycle.co.nz)

'My Photo Gallery' (http://gallery.unicyclist.com/albur10) has new
photos and has been generally re-arranged and spruced up. 9/9/03

------------------------------------------------------------------------
TonyMelton's Profile: http://www.unicyclist.com/profile/2118
View this thread: http://www.unicyclist.com/thread/28954

Yeah, Tony, as U-Turn says, the problem is spoke tension. Once I
upgraded to the airfoil rim and a KH36 frame (stiffer than the stock
Coker), I still experienced the exact same thing you are. Now, I no
longer have a hint of rubbing and although the KH is replaced with a
Hunter, the big change is to U-Turn's "The Strongest Coker Wheel in the
World". It's bombproof.

You can probably tighten your stock spokes quite a bit - maybe enough to
completely eliminate the problem. Try 1/4 or 1/2 turn at a time on each
spoke. Tight is right. Just make sure your spoke wrench fits right so
you don't damage the nipples.

---Nathan


--
nathan - BIG rides: Muni & Coker
------------------------------------------------------------------------
nathan's Profile: http://www.unicyclist.com/profile/251
View this thread: http://www.unicyclist.com/thread/28954

The Suzue hub is a fantastic hub, but is really quite narrow for that
size wheel. As a result, the spoke angle means that most of the spoke
tension is perceived radially by the wheel. Little of the tension is
seen laterally, which is required for lateral stiffness. On my 20", the
Suzue is a beautiful width and results in a nice angle and a super
strong wheel. The wide hub was designed (by Chris Reeder and George
Barnes) to be a nearly linear scale-up of width to match the increase in
diameter from 20" to 36", to achieve basically the same spoke angle as
the Suzue on a 20".

What I'm trying to say is that increased tension will help, but I'm not
sure that it will solve your problem because the geometry of your wheel
is inherently flawed. Even if you achieve the same tension I do (which
is painfully difficult, I'm sorry to say), there may not be enough of a
lateral component to stop the lateral flex. But this is one of the
reasons the Super wheel is actually super. It corrects a host of
problems, including the geometry and tension ones. There are many, many
steps to building a Super wheel, it takes a lot of time, and the
components are expensive. But the results are worth it.


--
U-Turn - Small fish, big pond

Weep in the dojo... laugh in the battlefield.

'Strongest Coker Wheel in the World'
(http://www.unicyclist.com/gallery/albup39)

-- Dave Stockton
------------------------------------------------------------------------
U-Turn's Profile: http://www.unicyclist.com/profile/691
View this thread: http://www.unicyclist.com/thread/28954

Couldn't've said it better. What he said!

---Nathan


--
nathan - BIG rides: Muni & Coker
------------------------------------------------------------------------
nathan's Profile: http://www.unicyclist.com/profile/251
View this thread: http://www.unicyclist.com/thread/28954

Slightly off topic, but is it possible to get proper stainless steel
spokes rather than the cheap galvanised ones that come on the Deluxe
Coker?


--
GizmoDuck - Cokernut

The NZ Unicycle Weekend Gallery
http://www.unicyclist.com/gallery/albut20
------------------------------------------------------------------------
GizmoDuck's Profile: http://www.unicyclist.com/profile/794
View this thread: http://www.unicyclist.com/thread/28954

U-Turn wrote:
*
Even if you achieve the same tension I do (which is painfully
difficult, I'm sorry to say), there may not be enough of a lateral
component to stop the lateral flex.
*

On a cautionary note, don't even try unless your wheel has a geometry
similar to U-Turns wheel.

When the rim of a tensioned spoke wheel is deflected from true the
spokes on one side get tighter and the spokes on the other side get
slacker. If the angle of the spokes is large then these force changes
are large and the wheel is stiff laterally. If the left and right spokes
are nearly vertical then there is very little change in tension and the
wheel is laterally soft.

These changes in tension are virtually independent of the static tension
in the spokes. When the rim moves to the side one set of spokes gets
longer and the other shorter, which is what causes the changes in
tensions. If the rim moves the same amount the spokes lengthen and
shorten the same amount regardless of the base tension, right? It's
just geometry. Since the elasticity of the spokes is pretty much a
constant (until they begin to yeild or permanently stretch), then the
changes in tension are pretty constant too. (Elasticity is the ratio of
length change to force change. Highly elastic materials lengthen more
under stress than inelastic materials, but they all lengthen under
stress)

So what happens when the base tension is high? If the spokes are nearly
vertical the rim isn't held laterally, and once it moves a little too
much to the side then it can dump the spoke tension by folding itself
into a nice potato-chip shape. Which it will most certaily do if you
tension up to U-turn's ultimate wheel tension without having the lateral
strength that his wider hub provides.

Just out of curiosity, where do your brakes rub? Have you tried marking
a pencil line on the braking surface and climbing a hill to see where it
gets scuffed off? (obviously don't deliberately apply the brakes when
you do this experiment.)

Good luck,

Tim


--
cyberbellum - Level 0.5 rider

If I knew what I was doing I wouldn't be in research...
------------------------------------------------------------------------
cyberbellum's Profile: http://www.unicyclist.com/profile/4550
View this thread: http://www.unicyclist.com/thread/28954

GizmoDuck wrote:
*Slightly off topic, but is it possible to get proper stainless steel
spokes rather than the cheap galvanised ones that come on the Deluxe
Coker? *
Yes it is. Tom Miller can provide you with them, or my wheels come with
them automatically.


--
U-Turn - Small fish, big pond

Weep in the dojo... laugh in the battlefield.

'Strongest Coker Wheel in the World'
(http://www.unicyclist.com/gallery/albup39)

-- Dave Stockton
------------------------------------------------------------------------
U-Turn's Profile: http://www.unicyclist.com/profile/691
View this thread: http://www.unicyclist.com/thread/28954