Chuck- As others have said, the cable is steel so it has an elastic (is will rebound to original length) portion of it's response to tension. If the tension stress is high enough the cable will plastically deform (stay stretched at the longer length). Cables are designed with enough strength to not pass into the plastic stage (unless bad stuff is going on like strands have broken first). If this were not so the cable would plastically stretch, it would then become work hardened and break soon. Just like the proverbial paper clip being bent back and forth (as opposed to just slipping a sheet of paper into the clip, over and over).
My understanding of "cable stretch" is as others have described. Every
aspect of the new system is molding, wearing in, settling in to their stable
points. It is common to have a new system (like a new bike) go through a
"break in" period in fairly few miles, then the system slows down it's
"loosening up" and stays fairly consistent for many more miles. It's not
that the rider is not using the system any less after this "break in"
period. It's that the system has found an arrangement of greatest stability.
>From this point on only minor pad wear is the majority of the future "loosening up".
<email@example.com> Sent: Wednesday, January 05, 2011 11:11 AM Subject: Re: [CR] Brakes and flex
> What is referred to as cable stretch, that is, the need to take up some
> cable after any new set-up, is the settling in of cable housing ends into
> the ferrules, the ferrules into their respective homes, etc.
> Of the engineers here, I'd like to ask a question. If we were to have a
> cable that stretched, say two millimeters over the distance of a rear
> brake run, would the cable stretch just those two millimeters and then
> stabilize? And, if so, why wouldn't it keep stretching?
> At the Interbike show a few years ago, I happened upon the Sram booth
> where, unless I misinterpreted what I walked in on the middle of, the guy
> was telling his audience that Sram had studied cable behavior and that
> they do not stretch in the use they recieve on bicycles.
> Chuck Hoefer
> Pacific Coast Cycles
> Oceanside, Ca.
> ----- Original Message -----
> From: "Jon Spangler" <firstname.lastname@example.org>
> To: "Dale Brown" <email@example.com>
> Sent: Tuesday, January 04, 2011 10:58 PM
> Subject: Re: [CR] Brakes and flex
Andrew R Stewart