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SpokeMaster

Bicycle Spoke Length Calculator

Calculate left and right spoke lengths from measured rim and hub geometry. SpokeMaster is designed for conventional J-bend bicycle wheels with equal spoke counts on each hub flange.

1

Rim

Use the actual rim ERD whenever possible.

2

Hub

Left and right are from the rider's perspective.

Left flange
Right flange
3

Lacing

Conventional equal-count left/right lacing.

SpokeMaster Measurement Guide

ERD

Effective Rim Diameter represents the diameter at the effective ends of two opposing spokes when their nipples are correctly seated. Manufacturer ERD can be a starting point, but an actual rim measurement reduces uncertainty.

Flange diameter

Measure the pitch-circle diameter through the centers of opposite spoke holes. Do not measure the outside diameter of the flange.

Center to flange

Measure laterally from the hub centerline to the center of each flange. Dished rear and disc-brake wheels commonly have different left and right dimensions.

Rim offset

For an asymmetric rim, enter the spoke-bed offset and the side it moves toward. SpokeMaster adjusts the effective left and right flange distances before calculating length.

How the calculation works

SpokeMaster treats the rim spoke position and hub spoke hole as points in three-dimensional wheel geometry. For each side it calculates the straight-line distance using rim radius, flange radius, effective flange offset, spoke count, and crossing angle, then applies the conventional J-bend flange-hole correction.

L = √(R² + r² + d² − 2Rr cos θ) − h/2 with θ = 4πc/N

Here, R is half the ERD, r is half the flange diameter, d is the effective center-to-flange distance, h is flange spoke-hole diameter, c is crossings, and N is total spoke count.

Scope and limitations

SpokeMaster v1 is intended for conventional bicycle wheels with J-bend spokes, an equal number of spokes on each flange, and standard cross or radial lacing. Proprietary straight-pull anchor geometry, 2:1/G3 patterns, paired-spoke systems, and other nonstandard arrangements should be calculated using the hub or wheel manufacturer's specified method.

Measurement references: Park Tool spoke-length guide · DT Swiss Spoke Calculator · Sapim Spoke Calculator
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