I've heard this question asked before, and it must be said that in order for a rear derailer to "hold" the selected cog during a downshift of the front derailer, THE PULLIES MUST REMAIN IN THE PLANE OF THE COG.
If one of the pullies were out of line, then as the cage rotated to take up chain slack there would be an effective lateral shift in the position of the chain relative to the selected cog.
Bent derailer hangers thus can and do result in the rear derailer ghost shifting in response to shifts of the chainrings as the cage rotates off-axis to the hub, cogs and axle.
I've heard mention of (newer?) Campagnolo derailers with the pullies offset WRT each other, but I have yet to see this. Could that be for spoke clearance? I doubt it!
David Snyder drinking beer in Auburn, CA usa
Subject: [CR]Suntour ARX
Rich Rhodes wrote:
> Can anyone tell me if the cage on a Suntour ARX (rear) der. is supposed to
> be perfectly straight and parallel with respect to the freewheel cogs?