Google Maps app lets me navigate (find directions/routing) along the public road network or pedestrian routes. Is there a way or an app that lets me load my own track network (http://radrouten.org/rr.kmz) and find the shortest path from A to B along my tracks?
Not that I'm aware of, no, you could try loading your tracks in google mymaps to have direct access to them from Google Maps though, or better from an app like Locus (see its topic for more details).
I'm doing the Google Maps thing already though it's not what I really want. It means I need to fix the smartphone to the handlebar, have the display light always on. With routing along my tracks I could leave the smartphone in my pocket and listen to the routing via headphones.