Tuning bike spokes by ear, with instructions you can act on

Wheel builders have tuned spokes by ear for a century: pluck each spoke like a guitar string and listen for the odd one out. A spoke under more tension rings at a higher pitch — the same physics as tuning any string. The skill isn't in the physics; it's in the ear, and in knowing what to do about what you hear. A phone can supply both.

Why pitch, not a tension meter

A spoke tension meter reads absolute kilograms-force, costs real money, and needs a conversion table per spoke type. A pluck measures pitch, which is free — but pitch only maps to absolute tension if you know the spoke's length, mass and elasticity. Rather than guess at those, the activity works relatively: what matters for a true wheel is that same-side spokes are even, and evenness is fully visible in pitch alone. Measure every spoke, compare each to the group, flag the outliers. Deviations are reported in cents — the musician's unit, one hundredth of a semitone — because that's the natural scale for "how far off is this string."

The part that's genuinely hard: which way do I turn this thing?

Every spoke-tuning guide founders on the same rock. A nipple wrench tightens one way and loosens the other — but "clockwise" flips depending on which side of the rim you're looking from, and a rider mid-repair is not in a mood for mental rotation puzzles. Getting this wrong doesn't just fail to fix the wheel; it makes the loose spoke looser.

So the activity never says just "tighten." It walks the wheel one spoke at a time and phrases each correction as a rotation plus the side it's seen from — the way you'd tell a friend holding the wrench. Direction is always knowable: pitch rises with tension on every wheel ever built, so a sharp spoke gets loosened and a flat one tightened, full stop.

The amount is not knowable up front — so it isn't invented

How many degrees of nipple rotation is "12 cents flat"? That depends on thread pitch and spoke elasticity — exactly the per-wheel constants the activity refused to guess when it declined to report absolute tension. Until the wheel has been measured, instructions size corrections honestly but vaguely: "a small correction," "a large correction."

To get real numbers, you teach it your wheel with one correction of known size: pick a spoke that needs moving, turn it a quarter turn, tell the tool what you did, and pluck again. The pitch difference between the two readings is the cents-per-turn constant for this wheel — and from then on, instructions come in eighths of a turn.

Small passes, not hero corrections

Corrections are capped at one turn per pass. That's not caution for its own sake: a wheel is a pre-stressed structure where every spoke's tension leans on its neighbors'. One large correction pulls the rim sideways in a way the next spoke then has to fight, and you end up chasing your own adjustments around the wheel. Several small passes converge; one big pass oscillates. The activity is built around that loop — measure all, correct gently, measure again.

Why this is an "activity," not a tool

Measuring one spoke's pitch is a tool — point, pluck, number. Truing a wheel is a job: set a baseline, measure 32 spokes in order, compare, adjust, re-measure, know when to stop. That's why spoke tuning ships as a guided activity — a sequenced procedure that keeps state across steps — rather than a raw frequency readout that leaves the hard parts to you. It runs on the phone (whose microphone can use the raw, unprocessed capture path) and in the web app, and a finished session can be saved into your object catalog: this wheel, this date, these tensions — so next spring you can measure again and see what winter did.

Curious what else the microphone can do? The tap test post covers ring-down analysis of fruit and materials, and the tools overview maps the whole territory.