Disc brake caliper alignment gets you close. The DT-3 Rotor Truing Gauge gets you closer. But if you want to put an actual number on rotor runout and work toward a measurable standard of straightness, the Park Tool DT-3i.2 Dial Indicator is the piece that completes the picture. It bolts directly to the DT-3 and replaces the gauge's visual estimation with a dial readout capable of resolving deviations down to 0.01mm — the kind of precision that matters when modern hydraulic calipers run pad-to-rotor gaps measured in fractions of a millimeter.

The v2 update introduces a fully adjustable elongated cylindrical tip designed to ride over the cutouts, voids, and irregular shapes found in most disc brake rotors. Earlier versions and generic dial indicators tend to catch on these features and give erratic readings. The DT-3i.2's tip geometry stays in contact with the braking surface through each rotation, which means the numbers on the dial actually reflect rotor trueness rather than rotor design. You get a consistent, repeatable reading you can work from.

The workflow is straightforward: mount your wheel in the truing stand, install the DT-3 on the stand's uprights, bolt the DT-3i.2 onto the DT-3, and spin the wheel. The dial indicator translates lateral rotor movement into a numerical readout, so you can identify the high and low spots, apply corrections with a DT-2 rotor truing fork, and verify your results in real time. Instead of eyeballing a gap or listening for rub, you're working toward a specific variance threshold. That distinction matters when you're chasing silence from a finicky caliper or prepping a bike for someone who notices every sound.... Read More