A bent derailleur hanger causes shifting problems that no amount of cable tension adjustment will fix. The Park Tool DAG-3 lets you measure hanger alignment and correct it without guessing, turning what used to be a frustrating diagnosis into a straightforward procedure. The gauge references off the rim surface at multiple points around the wheel, showing you exactly where the hanger has bent and how far it's off.

The tool threads into the derailleur hanger mount and extends an adjustable arm with a tip that sits at a fixed distance from the rim. You rotate the gauge around the wheel, checking the gap at twelve o'clock, three o'clock, six o'clock, and nine o'clock positions. Inconsistent gaps reveal the bend direction and severity. Once you know where it's off, you apply corrective pressure through the gauge itself—the robust construction handles the bending forces needed to straighten most aluminum hangers without damage to the tool or frame.

Modern drivetrains have tightened shifting tolerances considerably. An 11-speed or 12-speed cassette packs cogs closer together than older systems, which means hanger misalignment that might have caused occasional noise on a 9-speed drivetrain now produces constant hesitation or chain drops. The DAG-3 addresses this directly by giving you a reference accurate enough for current groupsets. It works on virtually every frame configuration—standard quick-release dropouts, thru-axle systems, and direct-mount hangers all accept the threaded indicator shaft.... Read More