Originally Posted by Alasdair
I was told by a young kid at a bike shop in the next county over. A friend of mine also said that when he bought his new Specialized Allez, that the LBS "prestretched" his chain along with the cables.
Sounds like they're repeating something they thought they heard someone else say. Or have been "hung" by the other more experienced guys. Sort of like sending a new wrench-in-training to the hardware store for elliptical ball bearings that go in worn out hubs. Or to look in the QBP catalog for transparent seatpost clamps or whatever.
Cables don't stretch, either, but housings compress, giving the illusion the cable got longer. Don't believe it? On a bike with well used housings, take a brand new derailleur cable and run it through the old housing and adjust the derailleur. Now go ride and note how it stays adjusted! The housings were already fully compressed. All major brands of cables are prestretched in a controlled fashion at the factory. No need in the shop. But we always compress the housings!