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Kevlar Spokes



 
 
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  #1  
Old July 10th 03, 08:41 AM
Phil, Squid-in-Training
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Default Kevlar Spokes

"Sheldon Brown" wrote in message
...
ed wrote:
I keep hearing about emergency kevlar spokes but can't find in my area.


Would you be able to lace a wheel entirely with kevlar cords? And have it
be useful/long-lasting?

--
Phil, Squid-in-Training


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  #2  
Old July 10th 03, 09:27 AM
Andrew Lee
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Default Kevlar Spokes


"Phil, Squid-in-Training" wrote in message

Would you be able to lace a wheel entirely with kevlar cords? And have it
be useful/long-lasting?


Kevlar has poor fatigue characteristics.


  #4  
Old July 10th 03, 06:38 PM
TBGibb
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Default Kevlar Spokes

In article , "Phil,
Squid-in-Training" writes:

Would you be able to lace a wheel entirely with kevlar cords? And have it
be useful/long-lasting?


There is a wheel like that, the Topolino, page 30 in the Colorado Cyclist
catalog. The kevlar/carbon spokes "span the entire wheel" and are held to the
hub by a sleeve (personal observation while drooling in CC's showroom). The
tension goes from side to side of the rim with very little tension on the
flange. No more elbows to break. I've no clue as the durability and will
certainly not be the first one on the block to have personal experience with a
set of them. But at $499.99 rear and $349.99 front I hope they are durable.
www.topolinotech.com

Tom Gibb
  #5  
Old July 10th 03, 07:56 PM
S. Delaire \Rotatorrecumbent\
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Default Kevlar Spokes



Andrew Lee wrote:

"Phil, Squid-in-Training" wrote in message

Would you be able to lace a wheel entirely with kevlar cords? And have it
be useful/long-lasting?


Kevlar has poor fatigue characteristics.


Were are the facts on this statement?
Having worked with Kevlar I would never had thought this to be true.




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  #6  
Old July 10th 03, 10:32 PM
Chalo
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Default Kevlar Spokes

"Phil, Squid-in-Training" wrote:

Would you be able to lace a wheel entirely with kevlar cords? And have it
be useful/long-lasting?


Maybe. Chafing of the surface fibers could be an issue, and might be
why composite-spoked wheels have used resin to encapsulate fibers into
a somewhat-rigid spoke. Spoke stretch (and therefore wheel rigidity)
would almost certainly be a problem, and it's difficult to imagine
what advantages such construction might have to offset its higher
material and development costs compared to a conventional wheel.

Spinergy Spox are one example of wheels made with synthetic fiber
spokes. The earlier Sugino Tension Disc used a web of aramid cords
radiating out in several diractions from each nipple, with the whole
web for each side sandwiched in plastic film.

Chalo Colina
  #7  
Old July 11th 03, 04:23 AM
Andrew Lee
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Default Kevlar Spokes


"S. Delaire "Rotatorrecumbent"" wrote in message
...

Kevlar has poor fatigue characteristics.

Were are the facts on this statement?
Having worked with Kevlar I would never had thought this to be true.


I guess to be accurate, it would be better to say how it is used. I got
this impression from a climbing perspective, where it is fairly common
knowledge that kevlar has poor flex fatigue and is that is a consideration
for cord where there is constant flexing. Thus you wouldn't want to tie
and untie knots in the cord regularly, but you can tie it once into a loop
for your Hexes (a form of rock protection or anchor). You can google this
for more information... I also found references to it loosing strength in
sail cloth applications (where they also found Kevlar had problems with long
term UV exposure, a problem that can be overcome though I think). I'll
leave it up to you to google for perhaps a more scientific paper with
testing...

I also found these old Jobst posts:

Ed Chait writes:

I would think that at least on a single speed, or fixed gear bike, a
narrow, toothed Kevlar belt and aluminum sprockets would be lighter,
cleaner, quieter and never require lubrication. I'm sure a belt
drivetrain has been tried before. Why has it never caught on?


It's good you say that in the subjunctive, there being no proof that
it is possible or practical. Kevlar is definitely not the medium, it
fails in fatigue as soon as it absorbs a little moisture, and it IS
hygroscopic. Kevlar has limited uses and timing belts is not one of
them.

Jobst Brandt avid G? writes:

Yes, that's the kind I also had in mind when replying, and it is such
belts where the Kevlar fibers break in fatigue with the absorption of
humidity. I doubt that anyone makes timing belts with Kevlar these
days. Their frailty must be common knowledge in the business.

A quick Excite net search revealed quite a few companies with sales
info for Kevlar reinforced belts. Maybe it's not a major problem for
certain products or conditions. I'd be curious to learn more.


We don't know where the Kevlar is and how it is used. It's somwhat like
the sticker "Intel Inside" on a product.

Jobst - do you have quantitative data, references or experience that
would be informative for the rest of us ?


I was involved in the development of paper moving plotters at HP
before their ink jet plotters. These plotters used timing belts to
move the carriage and paper (X&Y). We tested all sorts of belts and
discovered that, in the humidity chamber, all Kevlar belts failed. We
used conventional Rayon backed belts after that with no trouble.

No papers were published on these findings, they being insignificant
in that sort of work.

Jobst Brandt
ow, it may be that Kevlar is not "bad"
in fatigue characteristics when used in pure tension,it is doubful that it
can compare to steel operating at stress below the fatigue limit. I amnot
familar with how the fibers would be secured at the ends, but if there are
lots of bendsthat might cause problems with the constant stress cycling of
loading rolling wheel...I don't know for sure though. In what applications
have you worked with Kevlar?


  #9  
Old July 11th 03, 09:47 PM
Phil, Squid-in-Training
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Default Kevlar Spokes

Sugino T-Disc ( aka Tioga T-Disc) were 256 kevlar strands mounted in a
mylar
sheet. They were 32-hole format for use with a standard hub and rim and
worked just fine. They were actually lighter than 32 spokes. Really.
http://www.yellowjersey.org/wheel.html


Hey cool - I see my idea has some validity!

--
Phil, Squid-in-Training


  #10  
Old July 13th 03, 05:03 PM
Jasper Janssen
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Default Kevlar Spokes

On Fri, 11 Jul 2003 13:22:48 GMT, Jasper Janssen
wrote:

I wonder what would happen if, as a physics experiment, you laced a wheel
with a single steel cable, using appropriate sized pulleys at the hub and
the rim, and a single inline tension adjuster at one point. The pulleys
would have to have fairly heavy duty bearings to roll under 200 kg
tension, though, I don't think a bushing is gonna do that trick. On the
other hand, even at relatively severe deflections of the rim, the pulleys
would have very little actual movement to do in order to equalise the
spoke tension across the wheel.

Hmm. If 'spoke' tension is always equal on each of the spokes, then
there's no force holding up the hub, and thus the hub would fall down to
the ground instead of being held up.

Oh well, there goes my experiment.


As someone pointed out in email, I missed an important thing: As the hub
does its sagging, the "spoke"/wire angles change and provide a net force
upwards. So the wheel should behave more or less[1] as the
rigid-rim/rubber spoke model: as you're riding along, the hub will be
positioned slightly (or maybe a lot) below the center of the rim.


Jasper

[1] In several ways less, of course.
 




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