Originally Posted by
BCRider
Default? There must be something wrong with your bike. All of mine politely stay in the last gear I was in when I rode up to the house and stopped. Then when I go out to ride away the next time they are still ready to go in the same gear.
Because the systems use a pull cable and a return spring they need to default to one direction or the other. Which way makes no difference at all.... or perhaps it does. A short lived movement called "Rapid Rise" occured when Shimano tried to reverse the direction of the rear derrailleur so that it pulled to the smaller cogs and spring returned to the larger. In practice there were problems so the system was only around for a couple of years. To see what the reasons were try a search here on BF for "rapid rise" or check it on google.
I think the OP's meaning by "default" is "when there is no tension on the shifter cables," i.e., the position the derailleur(s) naturally goes to when the cable breaks, for example. It's a good question in that it seeks to understand a concept of basic derailleur design. Hope everyone's responses helped clarify. Keep wondering and asking questions. Curiosity spurs one to learning. OP, it'd probably be good to work on enhancing your bike vocab.