Originally Posted by
cyccommute
Some will say that cables don't "stretch" but even prestretched cables are still elastic. For example, a 1.1mm derailer cable of 60" length with 10 lb of force on it will stretch almost a millimeter in length. .
With all due respect, and I mean that sincerely, this is a bit of sloppy analysis well beneath you.
Yes, a cable does stretch under tension, but that happened the moment it was tensioned the first time, and the RD adjusted accordingly. Unless you somehow manage to adjust trim with the tension released, the tension based stretch is calibrated in and doesn't change. It wouldn't be different at a later time unless the cable was stretched beyond it's elastic limited and permanently distorted (not likely), or the RDs spring constant changed (even less likely).
Until then the tension based stretch won't change over time any more than a correctly calibrated bathroom scale would change it's readings from day to day.
BTW- As I said in my prior post, the cable will begin to stretch near the end of it's life as it frays and gets ready to fail completely. Consider this late stage stretch a warning sign and have the replacement handy.