On Wed, 12 Dec 2018 21:24:57 -0500, Frank Krygowski
wrote:

On 12/12/2018 5:29 PM, Theodore Heise wrote:
On Wed, 12 Dec 2018 17:15:45 -0500,
Frank Krygowski wrote:
On 12/12/2018 4:58 PM, Emanuel Berg wrote:
I thought the general problem was the cable loosed its
integrity or internal strength, so it got just a bit longer,
much like a bicycle chain, but enough to mess things up?

The cable itself is not going to get stretched with use, if
that's what you mean. That would require forces many, many
times larger than what's being applied in normal operation.

I think that's correct, and yet on my tandems I've sometimes seem
some changes in shifting that I attribute to change in cable
length--maybe more due to temperature changes than to actual
physical stretching. For example, when we go out on a very warm
day after having ridden in cold weather for a time, I often have
to tighten the adjuster just a smidge.

I think apparent increases in cable length are probably due to shifting
of position of the cable inside the housing, or wear of the housing
where the cable follows it through curves, or the end of the housing
settling further into a housing stop. Maybe the temperature change
triggers something like that?

As I've mentioned, my most frequent index shifting adjustment happens
with my folding bike, especially if its sat folded for a while. I've
learned it's easiest to just change the levers to friction mode for a
while, then re-try the index mode. Somehow, most of the misadjustment
corrects itself - I guess by the cables settling into their old
equilibrium position.

I'm pretty sure that if it were feasible to run the shift cable through
a straight, rigid tube all the way from shifter to derailleur, I'd never
see that problem.

If you are going to use rigid tubes why not a rod? Similar to the old
rod operated brakes. :-)

cheers,

John B.