Wheelbuilding glossary

The terms and jargon used across this calculator, explained in plain language. If a tool field or article ever loses you, it is probably defined here.

Spoke length & rim geometry

Spoke length: The straight distance from the hub flange hole to the rim — the number you cut or order. It is computed per side from flange diameter, centre-to-flange, ERD, spoke count and cross. On a dished wheel left and right differ, so they are calculated independently and never averaged.
ERD (Effective Rim Diameter): The diameter of the circle the spoke ends actually reach, measured to where the spoke seats inside the nipple — not the rim's outer or bead-seat diameter. It depends on the rim AND the nipples you use, which is why you should measure it yourself. ERD is the single biggest source of spoke-length error: a 1 mm ERD error moves each side by nearly 0.5 mm.
Offset / OSB (offset spoke bed): On an asymmetric rim the spoke holes are drilled off the rim centreline toward one side. That offset (OSB) evens out the left/right tension on a dished wheel. Enter it so each side corrects its length independently.
Dish: How centred the rim sits between the hub locknuts. A rear or disc wheel is 'dished' because the flanges sit at different distances from the centre, so the two sides run different lengths and tensions to keep the rim on the bike's centreline.
Cross (lacing pattern): How many other spokes each spoke crosses from hub to rim: radial (0x), 1-cross, 2-cross, 3-cross. More crosses means a more tangential spoke that carries torque better, and a slightly different (usually longer) length.
Radial lacing: A zero-cross pattern where spokes run straight out from the hub. Stiff and light, common on the non-drive side or front non-disc wheels, but it carries no torque, so it is unsuitable for driven or disc/braked flanges.

Hub

Hub: The centre of the wheel: the axle, bearings and the two flanges the spokes anchor to. Its geometry (flange diameter, centre-to-flange, width) drives the length and tension maths.
Flange: The disc at each end of the hub carrying the spoke holes. Flange diameter is measured to the spoke-hole circle (the PCD); a bigger flange shortens the spoke and braces the wheel more.
PCD (pitch circle diameter): The diameter of the circle the spoke holes sit on, centre to centre, on a flange. It is the flange diameter the calculator actually wants — measure to the hole centres, not the outer rim of the flange — and getting it right matters because it feeds straight into the length and bracing-angle maths.
Centre-to-flange: The distance from the hub centreline to each flange. The two sides usually differ — that is what creates dish — so each is entered separately.
Bracing angle: The angle a spoke leans sideways, away from the wheel plane, as it runs from flange to rim — shown per side (γ) in the build-angle readout. It comes from the centre-to-flange and flange diameter: the wider and lower a flange sits, the bigger the angle and the more sideways support that side gives. The low-angle (drive) side is the one that has to run higher tension to hold the rim centred.
OLN (over-locknut dimension): The hub width across the locknuts, e.g. 100, 142, 148 mm. It fixes how far each flange sits from centre and therefore the dish.
J-bend spoke: A spoke with a 90° elbow and a head that hooks through a round flange hole — the most common, easily replaced type. The elbow can flex and the head settles into the flange, part of why de-stressing matters.
Straight-pull spoke: A hub and spoke with no elbow: the spoke pulls straight out of the flange. Stiffer with nothing to settle, but it needs matching hubs and the maker per-side spoke offset, and length is 1:1 (a 1 mm measuring error is a 1 mm length error). A hub is one or the other, never both.
Drive side / non-drive side: Drive side is where the cassette/freehub lives (right, on a rear); non-drive is the opposite (left). On a disc front the reference flips to the rotor (non-drive) side. The drive/reference side runs the higher tension and shorter centre-to-flange.

Spokes & nipples

Spoke: The wire under tension that ties hub to rim. A wheel's stiffness is the rim plus the tension stored in its spokes.
Nipple: The small threaded nut at the rim end you turn to tension the spoke. Turning it onto the spoke raises tension. Nipples come in brass (durable) and alloy (light).
Butted spoke: A spoke thinned in its middle (double-butted = thinner centre, thicker ends). Lighter and more elastic, which actually helps a wheel hold tension. The thin centre is the section a tensiometer measures.
Bladed / aero spoke: A spoke flattened into a blade to cut drag and resist wind-up. Measured by thickness × width (e.g. 0.9 × 2.2 mm); pick the matching column on the tension table.
Spoke gauge: The spoke diameter, in mm (e.g. 2.0 / 1.8 / 1.5) or the old gauge numbers. It sets which tensiometer conversion column to use and barely affects length.
Leading spoke (ES: de tensión): On a crossed wheel, the spoke that leads from the hub in the direction of rotation (leans forward at the top). It stays relatively static under power and mainly carries braking torque. In Spanish we call it "de tensión".
Trailing spoke (ES: de tracción): The spoke that trails backward from the hub. It tightens under pedalling and carries the drive torque from hub to rim (the "pulling" spoke). In Spanish, "de tracción". Bringing leading then trailing up evenly avoids a localised hop.

Tension

Spoke tension: How hard each spoke is pulling, in kgf or newtons (1 kgf = 9.81 N). Too low and the wheel goes loose and fatigues; too high and you can crack the rim. It is a safety-critical number, always an estimate.
kgf (kilogram-force): The usual unit for spoke tension. Roughly 100–130 kgf is a typical rear drive-side target; always follow the rim's spec.
Tensiometer: The tool that estimates tension. It does not read tension directly: it measures how far the spoke deflects under a fixed load, and a per-(device × spoke) table converts that to kgf.
Deflection: The tiny amount a tensiometer bends the spoke sideways. The raw reading is deflection (or a dial number), not tension — hence the conversion table.
Conversion table: The maker chart mapping each reading to kgf for a given spoke section. We interpolate between its points and never extrapolate past its ends (out-of-range), because the curve is only known where it was measured.
Tension ratio: How the two sides compare, written as the lower-tension side as a percentage of the higher (e.g. 55%). On a dished wheel the geometry sets it: the side with the smaller bracing angle must pull harder, so a deeper dish means a lower ratio. The tension tool shows it and lets you cap the tight side, then derive the other from this ratio.
Tension balance: Getting every spoke on a side close to the same tension, and the two sides in the right ratio for the dish. An even, on-target wheel stays true far longer than a tight but uneven one.

Truing & building

Truing: Adjusting spoke tensions so the rim runs straight. Three things are trued: lateral (side-to-side), radial (up-and-down) and dish (centred between the locknuts).
Lateral true: Side-to-side straightness; a wobble is fixed by tightening spokes from the opposite flange where the rim pulls out.
Radial true (hop): Roundness; a high spot (hop) is pulled down by tightening the spokes there on both sides, a low spot by loosening.
Wind-up: The twist a spoke takes on as you tension it, because the nipple turns the whole spoke a little. Left in, it unwinds on the road and the wheel loses tension, so you relieve it as you build.
De-stress: Flexing the finished wheel hard (and re-truing) to force wind-up to release and J-bend heads to seat now, on the bench, instead of later on the road. Done repeatedly, it is what keeps a wheel true.
Markling Method: A fixed tensioning order (after builder Sam Markling): hand-tight the outboard high-tension spokes, then the inboard high-tension to ~two-thirds, then inboard low-tension, then outboard low-tension, and finally the outboard high-tension you left loose. It loads the rim evenly.
Quarter-turn: The unit of fine tensioning: a 90° turn of the nipple. The tension tool plans in quarter-turns, but turns are estimates, so re-measure as you go.