Originally Posted by
cyccommute
Myth not busted. Put any new cable in and watch the shifting deteriorate over the first few miles. I don't change housing as many times as I change cables. New cables always require adjustment shortly after installation. It's probably the number one complaint on the forums about new bikes. We get dozens and dozens of these kinds of post every week. I'll bet it's even the number one complaint you get as a mechanic.
Nope. I have personally put 300lbs of tension on various derailleur cables with a test jig here in the shop. The old SunTour braided cables would stretch a tiny bit, but that was 20 years ago. Current pre-stretched cables do not stretch until they near failure-which takes far, far more force than anyone can put on them with a shift lever.
Don't think housing can squish a little? We've tested that, too. Since it is virtually impossible to cut housing so that the end is completely square (without using a saw, or dremel tool, that is), housing tends to squish a little as the wire lengths equilibrate, and if you're using plastic ferrules, bed into the plastic.
Number one problem in my shop? Hardly. Since we actually understand what is taking place with cables, we know how to set up bikes so that they require little, if any, derailleur cable adjustments after the bike leaves. On custom bike builds, we dremel cut the housings and often use aluminum ferrules. Set 'em that way, and once it's done, it's done. We're the same way with our wheel builds. Tension relieved and equilibrated when they leave the shop, they don't need "little break-in tweaks".
Originally Posted by
cyccommute
Twisted cable, on the other hand, can untwist and lengthen quite easily. The lengthening process isn't very much but then it shifting is so precise now that it doesn't take much to throw it off. A millimeter would be hugh.
If you have, say, a mountain bike with 3 lengths of rear derailleur housing, that's 6 ferrules that all have to go through the bedding process. If every one moves only half a millimeter, you have 3 mm of slop! But most people will assume it was just "cable stretch" because everyone "knows" housings don't compress. Many shops with young employees don't understand this, and we're seeing here how these assumptions die hard.
You can
believe what ever you want, though.....