Derailleur Hanger Alignment

December 11, 2008 by  
Filed under Tips

In the early days of index shifting when the first systems were 6,7, and 8 speeds, derailleur hanger alignment was important, but not crucial to shifting. Due to the wider spacing between cogs, the derailleur hanger could be bent slightly, and the derailleur might still shift reasonably well. However, with the new 9 speed mountain bike cassettes (10 and now 11 speed for road), proper derailleur hanger alignment is absolutely imperative. Even a slight deviation of the hanger can cause incorrect shifting, and also cause the derailleur to shift into the spokes of the wheel, or jam the chain between the cassette and frame.

Whenever I build a new bicycle, I always check the derailleur hanger for alignment. Without fail, they are slightly bent (or worse) every single time. This cannot be avoided due to the initial fabrication of most frames, transportation, etc. A common mistake made by riders is to think, “I just bought a new hanger, so I will bolt it on and it will be straight.” The logic seems correct, but this does not take into account the fact that surface of the frame where the new hanger attaches is not necessarily aligned (usually it isn’t).

derailleur hanger alignment 300x300 Derailleur Hanger AlignmentThe replaceable derailleur hanger is a relatively new item, but it has saved many frames from the junkyard. In a crash, if the derailleur is near the smallest cogs, the derailleur will become bent severely – causing the hanger to become bent in the process. The replaceable hanger is designed to bend easily or break off in the event of a crash. Steel frames without a replaceable hanger can usually be bent back, unless the threaded hole has become elongated from an extreme bend. Aluminum will fatigue and fail after only a few cycles of bending. In the event that a non-replaceable derailleur hanger on an aluminum frame is bent, extreme care is required when it is aligned. There is a high likelihood that it will snap. Regardless, the hanger will be weakened, and will be more likely to bend in the future.

To achieve proper hanger alignment, a derailleur hanger alignment gauge is used. Using the rear wheel of the bicycle as a reference, the gauge is used to bend the hanger so that the hanger is in the same plane as the wheel. This is not rocket science, but it does take practice to prevent breaking the hanger. Due to the cost of the tool, it is probably best to have the alignment checked by a qualified shop when there is an issue with shifting, or after a crash.