The easiest way to fix your shifting by straightening your rear derailleur hanger
If you are an enthusiast mechanic that wants on his bike clean and crisp shifting and save trips and money to the local bike shop, then this is the tool for you. Truing your rear derailleur, adjusting limits and cable tension, can often be frustrating and the outcome may not be the one you expect. One of the most frequent issues with iffy shifting and drivetrain noise can be traced back to the alignment of your rear derailleur with the cassette, and the bike component responsible for that is the rear derailleur hanger. Derailleurs hangers are designed to save rear derailleurs and sacrificed in case of a severe crash, but this also means that they're prone to bending on minor impacts like bike falling, inadequate storage or transportation. A bent derailleur hanger will manifest as dodgy, inconsistent shifting and drivetrain noise that no amount of cable tension adjustments, limit-screw fiddling or chain cleaning will solve. The derailleur hanger alignment gauge helps you to straighten the derailleur hanger by measuring its relation to any point on the rim, and with incremental tweaks to have it perfectly aligned with the rim and sprockets. It's a very simple process, and it will fix any shifting issue that is not corrected by proper indexing.