Originally Posted by
MrEss
In fact, with the B-screw set totally loose (like, the same as if you unscrewed it completely and removed it), the top pivot never even moves as it shifts across my 13-30 cassette. Makes me wonder why this derailleur even has a top pivot.
On derailleurs with unsprung upper pivots like the SunTour, the top pivot is there so the derailleur can be moved out of the way when removing or installing the wheel.