Jun 19, 2026 · Germán Guía Delgado
A free, open Freespoke alternative: length, tension & truing
Freespoke (kstoerz.com/freespoke), built by Karl Stoerzinger, is the calculator most wheelbuilders learned on: a free spoke-length tool backed by a big, community-fed database of hubs and rims. It’s what inspired this project.
Spoke Calculator is a free, open alternative. The goal is simple: do the whole job, from the length math to the final true, without a login and without a paywall. Same free spirit as Freespoke, a bit more of the build.
What it does
- Spoke length: exact 3D-trig math, no approximations, with left and right computed independently for dished wheels. It has first-class support for asymmetric rims (offset spoke bed) and straight-pull hubs, which a lot of free tools quietly refuse. The formula and the intermediate values stay on screen, so you can check the math rather than trust a black box.
- Multi-tensiometer tension: more than Park Tool’s TM-1. Convert a reading to tension on Park TM-1, DT Swiss Tensio 2, Unior, Super B, Wheel Fanatyk, Hozan and more, pick a spoke by brand and model, then balance the wheel with a live radar, per-spoke status, dish guidance and a quarter-turn tuning plan.
- Truing simulator: a practice sandbox. Turn nipples and watch the tension spill over to the neighbours, and watch the rim’s dish, lateral wobble and radial hop react. It’s a teaching model, so treat it as practice and not as build advice.
The database
Spoke Calculator ships its own hub and rim database, built from each maker’s official specifications wherever they exist and hand-checked before it goes live. Every record carries its source and a confidence score, and anything without an official source yet gets flagged for review. The data is open, so it’s yours to use, double-check and improve.
How it differs
- vs Park Tool’s app: multi-tensiometer support instead of TM-1 only, and it also does length, dish and a simulator.
- vs paid or closed calculators: free, no account, open source (MIT) with open data, and the math is on screen for you to audit.
- vs Freespoke: Freespoke is great for spoke length, and Spoke Calculator keeps that free spirit while adding multi-tensiometer tension, a truing simulator, asymmetric-rim and straight-pull support, live visualisers and its own hand-checked database.
Tension figures are estimates. Devices drift and rims differ, so re-measure as you build, and don’t push a conversion table past its range. Everything runs in your browser, nothing to install. Start with the length calculator and tell us what’s missing. New to wheelbuilding? Skim the glossary and the fundamentals guide.