Rotor Truing Gauge

A bent rotor doesn't announce itself the way a out-of-true rim does. The wheel is true through the calipers and the brakes still rub somewhere in the rotation, or the lever feel goes mushy as the rotor's high spot drifts past the pad twice per revolution. The Rotor Truing Gauge 1689.2 turns that diagnostic from a guessing game into a direct read.

The gauge mounts into the accessory slot on the Pro Truing Stand 1689 or the Portable Truing Stand 1688 and indexes against the rotor face. Slide the indicator toward the disc, spin the wheel, and watch the gauge: a true rotor reads constant; a bent rotor reads the magnitude and the angular position of the deviation. Height-adjust to match the rotor diameter (160 / 180 / 200 / 220 mm rotors all work), then move the indicator inward until it's just touching the rotor face at rest.

The accuracy of this gauge is the difference between guessing where the rotor is bent and knowing. Once you know, the truing fork can fix it; and once the rotor reads constant through a full rotation, the caliper rub is either fixed or the caliper is the source of the problem, not the rotor.

Compatibility

• Truing stands: Pro Truing Stand 1689, Portable Truing Stand 1688.
• Rotor diameters: 160, 180, 200, 220 mm; all standard disc-brake rotor sizes.
• Rotor mount: works on both 6-bolt and Centerlock rotors (the gauge reads against the rotor face, not the mount).
• Max rotor thickness: 2.4 mm (covers all standard road and MTB rotors, which top out around 2.3 mm).

Specs

• Mount: indexes into the truing stand's accessory slot.
• Adjustment: height for rotor diameter, depth for rotor face position.
• Compatible with our Rotor Truing Fork 2.0 and Rotor Truing Fork 1666/2DP for the actual truing pass.

Built in Zreče, Slovenia

Unior has been forging hand tools in Zreče since 1919, and is the official technical partner of multiple World Tour and downhill teams. The 1689.2 is the disc-brake-era complement to the wheel-truing workflow: rim truing tells you the wheel is round; rotor truing tells you the rotor is. Most workshops add this gauge to the truing-stand kit the first time they spend ten minutes chasing a brake rub that turned out to be a rotor problem.

Pro tip from our mechanics

Read the rotor first, then read the wheel. A wheel that runs true through the calipers but rubs the caliper at one point in the rotation almost always has a rotor problem, not a rim problem. Mount the 1689.2 before you reach for spoke wrenches; ten seconds of rotor diagnosis saves twenty minutes of unnecessary truing. The full disc-brake-era truing workflow is in How to true a bike wheel →