Kevlar Cables (not Casings)

Postby thekiwi on Tue 19/Mar/13 4:01pm

Hi all

Just wondering if anyone has ever heard or see of such things: Kevlar cables.

Ive just taken delivery of a bike to replace my broken one, and its got a Kevlar front derailleur cable ... there isnt a bit of Stainless steel in it.

It has a white outer "layer" which is soft ... not at all like a normal casing. On cutting it to length you can see the brown fibres inside which are literally like a very very fine cotton. Its so pliable you can wrap it around your derailleur bolt a couple of times.

Had a quick search online but cant find anything which remotely resembles it ... and it intrigues me... :)
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Re: Kevlar Cables (not Casings)

Postby Velocipedestrian on Tue 19/Mar/13 4:14pm

Ooh, fancy.

Never heard of it, but like the idea of rustproof.
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Re: Kevlar Cables (not Casings)

Postby Joel on Tue 19/Mar/13 4:20pm

what is the new bike?
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Re: Kevlar Cables (not Casings)

Postby danose on Tue 19/Mar/13 4:21pm

thekiwi wrote:Had a quick search online but cant find anything which remotely resembles it ... and it intrigues me... :)


http://www.powercordz.com/derailleur-ca ... -set-1-2mm
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Re: Kevlar Cables (not Casings)

Postby Kiwicyclo on Tue 19/Mar/13 9:00pm

Joel wrote:what is the new bike?


Narrow it down . . . .it is a GIANT of course, not a Propel, but has an integrated seat post (?) and an orange and blue scheme :sly:
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Re: Kevlar Cables (not Casings)

Postby Joel on Tue 19/Mar/13 9:28pm

since I asked I saw your Facebook photo.. HOT!
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Re: Kevlar Cables (not Casings)

Postby thekiwi on Tue 19/Mar/13 10:30pm

danose wrote:
thekiwi wrote:Had a quick search online but cant find anything which remotely resembles it ... and it intrigues me... :)


http://www.powercordz.com/derailleur-ca ... -set-1-2mm


thx Danose, that's them. can see them here in close up.
http://m.pinkbike.com/news/power-cordz-review-2010.html
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Re: Kevlar Cables (not Casings)

Postby Simonius_Titius on Wed 20/Mar/13 1:51am

Steel cables give some warning before failing, I wonder what these do. Sounds nice for gears and back brake anyway.
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Re: Kevlar Cables (not Casings)

Postby danose on Wed 20/Mar/13 11:14am

thekiwi wrote:thx Danose, that's them. can see them here in close up.
http://m.pinkbike.com/news/power-cordz-review-2010.html


the 'don't stretch like steel cables' bit in the marketting annoys me - stainless gear cables DO NOT stretch (what people attribute to cable stretch is just endcaps etc settling on housing - or under tightened clamp bolts).

As for rust - I don't think their housing is all synthetic (cos it's really hard to make a compression resistant outer without using wire) - and generally I find it's the housing that rusts (using coated inner cables) and kills shift performance (double sealed xtr endcaps cures most of that - there's always gore's fiddly system if you want the ultimate)

really, if you want silky smooth shifting and no cable hassles, just go electric shifting :satan:
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Re: Kevlar Cables (not Casings)

Postby Conners on Wed 20/Mar/13 11:58am

danose wrote:the 'don't stretch like steel cables' bit in the marketting annoys me - stainless gear cables DO NOT stretch (what people attribute to cable stretch is just endcaps etc settling on housing - or under tightened clamp bolts).

I think there is a trainwreck lurking in here somewhere?
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Re: Kevlar Cables (not Casings)

Postby thekiwi on Wed 20/Mar/13 12:16pm

Conners wrote:
danose wrote:the 'don't stretch like steel cables' bit in the marketting annoys me - stainless gear cables DO NOT stretch (what people attribute to cable stretch is just endcaps etc settling on housing - or under tightened clamp bolts).

I think there is a trainwreck lurking in here somewhere?


It is certainly different looping the "cable" around the anchor bolt twice to ensure it grabs.

They say the stuff is stronger than a typical cable but will wait and see how this thing performs. Thankfully its just the front derailleur at the moment.

Might be good for less "rattle" on the internal cables in the main tube !! :)
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Re: Kevlar Cables (not Casings)

Postby danose on Wed 20/Mar/13 12:51pm

thekiwi wrote:It is certainly different looping the "cable" around the anchor bolt twice to ensure it grabs.


plus if you break a cable in the field you can put your boy scout skills to work fixing it - question is do you use a double fishermens or a reef knot? :D

Might be good for less "rattle" on the internal cables in the main tube !! :)


see above statement about going electronic :p
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Re: Kevlar Cables (not Casings)

Postby Simpleone on Wed 20/Mar/13 6:23pm

The Powercords ones work fine have sold and used them for years. Even if the outer white coating cracks they still hold. Cut them with a sharp blade or scissors, they generally outlast any metal cable. Never used them on road bikes though only on MTB's but imagine they would be fine.
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Re: Kevlar Cables (not Casings)

Postby Simonius_Titius on Wed 20/Mar/13 7:02pm

Conners wrote:
danose wrote:the 'don't stretch like steel cables' bit in the marketting annoys me - stainless gear cables DO NOT stretch (what people attribute to cable stretch is just endcaps etc settling on housing - or under tightened clamp bolts).

I think there is a trainwreck lurking in here somewhere?

Certainly a lost lunchtime, this looks more fun than chain stretch.

Some gear inner cable is advertised as "pre-stretched" and needing less settling in.

A manufacturer of heavy duty wire cables gives stretch as 0.25% to 1% depending on load and construction.
Note that the bulk of the steel does not stretch but the cable rearranges itself internally, perhaps with some micro hotspots which exceed yield stress.
http://www.bergencable.com/technology/technology_cable101.html


Here is a graph of small-cable stretch over two million load cycles. It shows stretch being very much higher in the first 50,000 cycles, though only being 0.05% i.e. 0.6mm over 1600mm in this case.

They also give 120kg as breaking strain for a 1.2mm cable. If a rear derailleur cable needs 10kg? at the shifter end the cable will stretch a bit even in the straight runs.
http://www.savacable.com/pages/LowStretchCable.html


The formula for minimum bending radius for a cable is
[never mind, an optimal bend is way too big to fit on a bike]
so there will be a lot of extra "stretch" as the cable settles itself into the bends.
Some of these bends can be avoided by using pivoting cable and housing stops. Both were done on derailleurs until the mid 1980s.

All top quality brakes used to have pivoting brake housing stops where the screw swings in an unthreaded D shaped hole as below (and falls out if the cable is removed).
BR-7400 oversize adjuster for 7x6mm hole detail - flickr.stronglight.jpg


Please don't lose these bits if you are removing old brakes. You can screw them back onto the brake using the thumbwheel on the bottom so it doesn't get lost. If you are troubled by an excess of orphan thumbwheels send them to me. I would be especially delighted to find the obnoxious super-nonstandard Dura-Ace steel collar/insert barely visible in the picture. :)
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