Re: How many strands of wire in a cable? Twist rate?

Carl Fogel wrote:

Chalo wrote:

Whether the elasticity of a 19-strand
cable is significant within the relevant range of tensions I simply
don't know. However, the additional stretch in a 7x7 rope lay cable is
easy to discern. I have assumed that this is due to relative movement
of the 49-strand cable's less compacted filaments.

So it's seven strands wound together to make a bigger strand, and then
seven of those bigger strands wound together to make a coarser cable
than a 1 inner x 6 middle x 12 outer single strands.

Such a cable is not only coarser in texture, but it has more internal
voids than a 1x19 cable of equal cross-sectional area. These seem to
be the physical source of the "constructional stretch" described at the
link you provided.

Here's an interesting page with a stretch calculator and some
comments. It assumes the 7x7 construction that you mention, stainless
steel wire, and "60% proof loading":

http://www.spaceagecontrol.com/calcstre.htm?MA%5B0%5D=50&MA%5B2%5D=60&MA%5B1%5D=0.04&Submit=Calculate

When I enter values that would be characteristic of a rear brake cable
on one of my bikes (1.6mm dia, 200 lbf, and 38" length, I get stretch
quantities of about a quarter inch, roughly one third of the usable
range of a conventional brake lever. This is apart from compression in
the cable housing and flex at the anchor points. It makes sense in the
context of my experience with 7x7 cables.

Many nicer-quality 1x19 bike cables are die drawn (e.g. Quality
Cables). The drawing process gives them a noticeably smoother surface,
and it is on this basis that they are marketed. However, I think that
drawn cables are certain to have much less constructional flex than
undrawn cables, as well as having more cross-sectional area for a given
outside diameter.

Chalo

.

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