Where the number comes from
A spoke under tension is a bar in elastic extension. Its stretch is the tension times its length divided by its cross-sectional area and the elastic modulus of the wire. Turning the nipple does not change the tension directly — it shortens the distance the spoke has to span, and the spoke resists by stretching further. One full turn pulls the spoke through by exactly the thread pitch.
So the tension change per turn is the spring rate of the spoke multiplied by the pitch. The spring rate is the modulus divided by the sum of length-over-area for each section of the spoke, which is why a butted spoke has to be treated as two materials in series rather than as a single average.
Two consequences fall straight out. Long spokes are softer than short ones, so a nipple turn on a 700c wheel is worth less tension than the same turn on a 20 inch wheel. And a thread pitch of a bit under half a millimetre means the whole working tension of a spoke — from slack to a hundred kilograms force and more — lives inside about one and a quarter turns of the nipple. That is the reason wheelbuilders talk in quarter turns and eighths rather than in turns.
Why butted spokes hold tension
| Spoke | Relative compliance | Behaviour in the wheel |
|---|---|---|
| Plain 2.0 mm | Stiffest | Comes up to tension fastest, drops furthest for a given amount of settling |
| 2.0/1.8 double butted | Softer in the middle | More elongation stored at the same tension, more forgiving of bedding in |
| 2.0/1.5 heavily butted | Softest | Most stretch per newton, most turns to build, and the most tolerant of movement |
The intuition that a thinner spoke is weaker gets the mechanism backwards for this particular question. A thinner middle section does not carry less load in a built wheel; every spoke on a side carries whatever the geometry gives it. What the thinner section changes is how much the spoke elongates at that load, and elongation is a buffer. When the rim seats, the elbows bed into the flange and the nipples settle, the wheel loses a fixed amount of length in a lot of small places, and that loss costs a stiff spoke more tension than a compliant one.
The same effect matters under riding load. A spoke passing through the bottom of the wheel is momentarily unloaded, and the deeper it dips toward slack the harder the elbow works. More stored elongation means a smaller share of the tension is given up on each revolution, which is a fatigue argument rather than a strength one.
What the model leaves out, honestly
The figure this page produces is the ceiling. A wheel is not a spoke bolted to a wall: the rim is a curved beam that deflects toward the hub as the spokes pull on it, the flange flexes, and the interfaces bed in over the first few tension cycles. All of that movement absorbs nipple travel that would otherwise become tension, so the measured change per quarter turn on a real wheel comes out lower than the elastic calculation — sometimes much lower on the first pass through a fresh build, and closer to it once the wheel has been stress-relieved and settled.
It also assumes the thread does not wind up and the spoke does not twist. Both happen. A spoke gripped by a nipple that is stiff to turn will wind up along its own axis before it starts to stretch, and that twist unwinds later and takes tension with it, which is why builders hold the spoke with a key and go slightly past then back.
None of this changes the useful conclusion: the ratio between a quarter turn and a full one is exact, and the comparison between two spoke types is reliable even where the absolute numbers run high.
Reading tension at all
The calculation is about changes, not about absolute tension, and it takes both endpoints from you. A tensiometer converts spoke deflection under a known load into a force, using a conversion table specific to the tool and to the gauge of spoke. That is the only practical way to know where a wheel actually is. Pitch by ear tells you whether spokes match each other, which is genuinely useful for evenness, but the frequency depends on the free length as well as the tension so it is a comparison rather than a reading.
Whatever number you aim for belongs to the rim. Deep carbon sections, box-section aluminium rims, eyeleted and non-eyeleted designs all tolerate different loads at the spoke hole, and the failure — a crack radiating from the nipple seat — appears well after the build. That is a manufacturer figure and the calculation on this page cannot substitute for it.
Questions people ask
How much tension does a quarter turn add?
It depends on the spoke, which is the point of the calculation. On a 292 mm double butted 2.0/1.8 spoke with a standard 56 thread per inch nipple, the elastic model gives roughly 21 kgf per quarter turn; the same length in plain 2.0 mm gives about 25. On a real wheel the measured change is lower than either, because the rim and the seats absorb part of the movement.
Why does the calculated change look higher than what I measure?
Because the model treats the spoke as the only thing that moves. In a wheel the rim pulls inward slightly under the spoke it is being tightened by, the flange flexes, and the elbow and nipple seat bed into their surfaces. All of that eats nipple travel. Expect the gap to be widest on a new build and to narrow once the wheel has been settled and stress relieved.
Do butted spokes really need more turns?
Yes, and by a predictable amount. The reduced middle section stretches more per unit of load, so a given nipple travel produces less tension. For a 2.0/1.8 spoke with a long butted section the ratio is around 1.15 to 1.2 turns for every turn a plain gauge spoke would need. That extra compliance is why the wheel holds tension better as it beds in.
What thread pitch do spoke nipples use?
The two figures in the selector, 56 and 44 threads per inch, cover most of what you will meet, and they correspond to about 0.454 and 0.577 mm of travel per turn. If you have anything unusual, or you want to be certain, measure the travel across ten turns on a spare spoke and divide, then enter it as the measured pitch.
Can I use this to decide a target tension?
No, and the page does not offer one. What tension a wheel should carry is set by the rim, and it varies with depth, material and whether the spoke holes are eyeleted. Take the figure from whoever made the rim, read the actual tension with a tensiometer, and use this calculation only to work out how far to turn to get from one to the other.