Originally Posted by
dedhed
Directly from your link. Construction stretch is taken out of the equation by pre stretching, not to mention at installation during adjustment. Yes, construction stretch is a thing but typically doesn't play into shifting issues after a proper installation.
FWIW I've installed enough new cables to know readjustment is needed sometime after a cable is installed, whether that's from things bedding in, taking up initial construction stretch,or other factors.
Structural Stretch
Structural stretch is the lengthening of the lay in the construction of cable and wire rope as the individual wires adjust under load. Structural stretch in Loos and Company products is less than 1% of the total cable length. This form of stretch can be completely removed by applying a cable or wire rope prestretching operation prior to shipment.
The Bethlehem Elevator Rope site gives values for construction stretch of prestretched cables. I also think the “completely removed” statement may be application dependent. If you are running miles of cable of thick cable, a little bit of left over construction stretch may not matter much. For a bicycle application, the system can deal with the small amount of elastic stretch. But even a small amount of construction stretch can initially throw off the precision of index shifting. I’m not saying that the construction stretch is all that much but it is there and it is enough to require new cables to be adjusted after the initial stretch is gone.
One thing I’ve taken to doing is to run through several shifts without pedaling on a new inner cable install. I’ve found this goes a long way towards getting rid of the need to make big adjustments down the line.