such as titanium or thick aluminum hangers, are hard to realign without breaking them. While a visibly bent hanger obviously needs some help, it doesn’t take much misalignment to cause shifting trouble. A classic symptom of a misaligned hanger is being able to dial in your shifting in 2-4 cogs at the high end of the cassette only to have the indexing degrade in the middle and skip on the low end. Adjust for the center of the cassette and neither the very high or very low gears work well—it’s time for an alignment. For better or worse the only tools available to align a rear derailleur are shop-quality and shop-price, and while few home shops have them at their disposal most bicycle co-ops should have one on hand, and most medium to large cities have a co-op shop space.

1. Remove derailleur and thread alignment tool into hanger in its place. Starting at the 12 o’clock position, set indicator arm to touch the rim at the valve stem, and lock into place. Using the same point on the rim for measurement ensures that the trueness of the rim does not affect hanger alignment.

2. Rotate tool and wheel 180° to the 6 o’clock position, sliding indicator arm to meet the rim sidewall. If the gauge is barely touching the rim, the hanger is aligned in that direction. If the indicator arm is either interfering with or has a gap between it and the rim, the hanger is out of alignment. Repeat at the 3 and 9 o’clock positions.

3. If the hanger is out of alignment, use the tool itself to gently bend the hanger back into alignment in small doses, checking progress along the way. The hanger can be likened to bending a paperclip back and forth—the less movement to get it right, the more likely the alignment will hold and the less likely the hanger will break.

It may be tempting to simply grab hold of the derailleur and bend it back into place visually aligning the pulleys with the cassette, but this is not recommended. Not only is your eye terribly inaccurate as compared to the proper tool, you risk bending the derailleur cage itself, furthering the misalignment and requiring a more expensive fix.