How a Spoke Tension Meter Works — and Why the Conversion Chart Matters
What the meter actually measures, why its number isn't tension, and the two very different ideas of "calibrated" — with links to the original post.
A spoke tension meter is the tool that turns wheel building from feel into measurement — but its dial doesn't read tension, and two meters can disagree by design. Here's what's actually going on inside one, from a workshop that has thought hard about it, with the source.
1. What the meter measures
The meter doesn't measure tension directly. It presses the spoke at three points — two fixed, one movable — and reads how far the spoke deflects under that fixed sideways push. A tighter spoke resists more and deflects less. So the dial shows a deflection, and you look that deflection up in a conversion chart to get the tension. Crucially, the relationship between deflection and tension is a bowed curve, not a straight line.
Source: Nomu Lab #1011
2. Why you can't skip the chart
If the deflection-to-tension relationship were a straight line, and if everyone used a single spoke type, you could mark the dial in tension units directly. Neither is true: the curve is bowed, and spokes come in many gauges and profiles, each with its own curve. So the meter is useless without its conversion chart — the dial number means nothing on its own.
Source: Nomu Lab #1011
3. Two ideas of "calibrated"
The two common meters embody opposite calibration philosophies:
| Hozan | DT | |
|---|---|---|
| Chart | Individually made for that one meter (publicly inspected per unit); not interchangeable with another meter's chart | One universal chart for all meters of the type |
| Calibration | Do not touch it; send the meter back to the maker to recalibrate (a new chart comes with it) | You adjust the meter so it matches the universal chart — user-recalibratable against a known-good reference meter |
| Coverage | 13/14/15g plain spokes only — explicitly not aero or special spokes | Per its chart |
Both drift with age, like a torque wrench. The important question for any measuring tool is whether it can be recalibrated — keep the chart safe, and don't fiddle with a Hozan's calibration screw.
Source: Nomu Lab #1011
4. Same reading, different spoke
Because thick and thin spokes have differently-shaped curves, the relationship between the dial reading and the converted tension isn't the same proportion for both. A practical consequence: build two rears, one all-Competition and one all-CX-Ray, both equal-gauge and both with the drive side set to the same converted tension — and the all-CX-Ray wheel ends up with a smaller left/right tension difference, and a non-drive side that feels tauter to squeeze. The spoke's profile changes the balance even when the target number is identical.
Source: Nomu Lab #1011
5. A workshop's "three tensions"
The workshop separates what people loosely call "spoke tension" into three of its own ideas — useful for understanding why a wheel with correct numbers can still feel different:
- 1st — the raw deflection the meter reads.
- 2nd — the actual tension after the chart conversion. This is what everyone normally means by "spoke tension."
- 3rd — not a tension at all, but a number that folds in the spoke's cross-section and its angle to the hub. The workshop finds it tracks a wheel's drive feel better than plain tension does — because radial and crossed spokes transmit drive differently at the same tension, so angle matters, and so does cross-section.
Source: Nomu Lab #1011 — On tension meters and the third spoke tension
Measure, but understand what you're measuring
A tension meter is essential, but the number it gives is one input. See what tension does to a wheel in the spoke tension guide, and how the two sides differ in the asymmetric wheel guide. Start a build from the Wheel Building Guide. Every claim here links into the Nomu Lab Diary archive.