Brake Cable Gauge

Optical free-play measurement & adjuster calculator

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1 · Scale calibration not set

Put a known object flat in frame, in the same plane as the lever tip. Tap its two ends on the video, then enter its real length.

Reference length (mm)

Scale: —

2 · Measure free play

Drag the green box onto the lever tip (or pedal tip). Hold the button, pull slowly from rest to the point the brake first bites, then release.

0spec40 mm

3 · Caliper / pad check

Same tap-two-points ruler, aimed at the caliper. Measure each pad's friction material and the gap to the rotor on both sides. Uneven = sticking piston or a dragging slide pin.

	Pad thk	Gap
Piston side	—	—
Outer side	—	—

4 · Front vs rear

Brake	Free play	Spec	Off by
Front	—	—	—
Rear	—	—	—

Spec & hardware

Free-play spec for front — edit to match your service manual

Min (mm)

Max (mm)

Adjuster thread pitch (mm/turn)

Lever ratio (tip ÷ cable arm)

Ratio = distance pivot→where you measure, divided by pivot→cable anchor. Eyeball it: most brake levers land near 4, most rear pedals near 3. It only scales the turns number, never the measured mm.

Brakes are safety critical. This is a measuring aid, not a service manual. Confirm spec values for your bike, torque the locknut after adjusting, and test at walking pace before riding. Never adjust so far that the lever has zero free play — the shoe or pad will drag and cook.

Haptics use the Vibration API — Android Chrome/Firefox only. iOS Safari has no vibration: the app beeps and flashes instead.