Originally Posted by
Dominae
I am fairly certain that it began after I had a crash in a race in October 2011. The problem persisted through the end of the season,
Why wouldn't the twisted rear derailleur affetc the shifting when it is on the large front chain ring? It seems that you would have the same degree of twist whether the chain is on the large or small chaniring and so the alignment would be imporper in either case.
The timing certainly fits with my deduction. No, the amount of misalignment can indeed change with the rotation of the pulleys. To illiustrate that, place your hand in front of your face, edge on and vertical (fingers pointing straight up, thumb toward you) and sight past your fingertips to a fixed vertical item (door frame for example. Now rotate your hand forward so that your fingers point forward at a 45 degree angle. Notice your fingertips are still in line with the target.
Now go back to the original position but turn your hand slightly to one side like a rudder, so that you can now partially see your palm. Again make sure you are sighting over your fingertips to that vertical plane. Now rotate your hand forwrd
in the vertical plane the same as before to 45 degrees. You will see that your fingertips are now to the left of the target.
Your hand is the pulley assembly, the target is a cassette cog. When your hand is upright it is on the large chainwheel, when it's pointed forward it's on the small one.