Roadies and mountain bikers plagued by shifting problems may serve themselves well by first examining the health of their inner and outer cables. Those unable to solve shifting issues with a simple cable tension adjustment or who experience stiff action at the shift lever should strongly consider starting from scratch with new cables.
The ease with which the inner cable travels through the outer cable is paramount to superior shifting performance, especially at the rear derailleur where only a small amount of travel is required to make a clean and easy shift. Here, a compromise in travel as little as 1-2mm can adversely affect shifting performance. Cable travel can be impeded by a corroded inner cable, a bent outer cable, an outer cable whose inner wire strands have pulled through the casing (which may not be revealed without removal of the ferrule), or simply too many rides in the rain or mud.
Replace your inner and outer cables with high quality parts such as those offered by companies such as Shimano or Jagwire. These high performance cables are coated with Teflon (often designated PTFE) and are extremely weather resistant. Or you may use Gore’s new “Ride On” system, which completely encloses your inner cable from the shifter to the derailleur during the spans which are not covered by an outer cable.
Having replaced both inner and outer cables, you will find cable adjustment easier and action at the shift lever greatly improved.