[Frank Röder]

These other 15-20% of breakdowns could be results of an accident (f. e. the deformation of an important part) or damaged shoe belts or relaxed screws (and not the right tool in your bag) or a broken break saddle or calf frame. May be these beakdowns are more rarely than 20 %.
Another probelm are broken poles or loosen pole ends, but in this case you can continue your tour.

Frank

A new epereince, this evening: The bearing of may back wheel locked nearly complete suddenly. The only way to continue my way, was to chance the wheel.