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Governor Rope-Speed Calculator

Groove-wear compensated. The tach reads the sheave; the code cares about the rope. This turns one into the other using a measurement instead of a nameplate.

Measure

  1. Straightedge across the sheave rim, spanning the groove.
  2. Depth gauge from the straightedge down to the rope crown, perpendicular to the straightedge — that reading is the proud height (or depth, if the rope rides below the rim: enter it negative).
  3. Crown (outside) diameter of the sheave with a tape or large caliper.
  4. Rope diameter from the crosshead data tag, or measure it.
  5. Run the trip test: ramp slowly, read the tach with max-hold on, enter the reading below.
straightedge ══════╤═══════════════╤══════ │ proud height h ↕ ● ← rope crown ( ) rope, dia d pitch dia = C + 2h − d ──────── sheave rim, crown dia C

Inputs

Fill the first four fields and the numbers appear.

What the correction factor is telling you. It is how much the groove wear and rope geometry are bending the raw tach number. On a healthy sheave it sits near 1.00 and the drift is a few ft/min; a factor drifting away from 1.00 over the years is the groove deepening — which is itself worth a line in the report.
Pass/fail comes from the book, not from this page. A17.1 wants the mechanical trip at minimum 115% of rated speed; the maximum is per §2.18.2, "Tripping Speeds for Speed Governors" (clause number and title confirmed from the A17.1-2022 table of contents) and depends on rated speed — read the table for the unit in front of you. This calculator makes the measured number honest; it does not judge it. And if the tach lets you enter a custom wheel circumference (Shimpo DT-105A and Checkline CDT-2000HD-TE both do), you can key in the pitch circumference directly and skip the correction entirely — this page then serves as your check.
While the straightedge is out. Lay it across all the grooves: a rope riding lower than its neighbours means unequal tension or uneven wear, caught early. Eyeball pass/fail is enough; measure and document only what the straightedge flags. — standing five-year practice, Adam, 2026-07-31