About

I'm Ger, and I build my own bicycle wheels. Not for a living — for the same reason I do all my own maintenance: it's how you actually learn, and the mistakes are what give you the experience. Spoke Calculator is the tool I wish I'd had when I started: exact spoke lengths, multi-tensiometer tension, and a truing simulator, backed by an open hub and rim database. Free, no login, everything in your browser.

Where this started

My wheelbuilding started on a forum. Years ago on foromtb, deep in a thread called «ruedas endureras a la carta» — custom enduro wheels, built to order — I read enough people lacing their own that I stopped outsourcing it and bought my first set of spokes. The first wheel was humbling. The second less so. I've hand-built fourteen-plus wheelsets since, through folders, hardcore enduro, gravel, fatbikes and rigid steel, and I still get the same quiet satisfaction every time one comes up to tension and runs dead true.

The tool almost everyone leaned on was Freespoke (kstoerz.com/freespoke), Karl Stoerzinger's free spoke calculator with its huge community-fed database. It's the one that got me into wheelbuilding in the first place, and it's still right here.

What this is

I built Spoke Calculator because I wanted one place with everything you need to calculate and build a wheel: exact spoke length, multi-tensiometer tension, a truing simulator, and an open hub and rim database I validate by hand. Same free spirit as Freespoke, all in one place — plus the things I always wanted: asymmetric rims, straight-pull support, and live visualisers that show what the math is doing. No account, nothing stored on a server.

Data & licence

• Hubs & rims: geometry comes from the manufacturer's official specifications wherever they exist, and every value is hand-validated before publishing. Where there's no official source, it's flagged for review.
• Tension: each conversion comes from the tensiometer's own published table. These are safety estimates — always re-measure.
• Code: MIT, open.

How the numbers are made

Spoke length is pure 3D trigonometry — no approximations — and the formula and intermediate values are shown so you can check the math. Tension conversions come from each tensiometer's published table, verified against the manufacturer source where one exists; figures are estimates (devices drift, rims differ), so always re-measure as you build. The truing simulator is a qualitative teaching model, not build advice.

Get involved

Build wheels and spot a number that looks wrong? Missing a hub, rim, tensiometer or spoke? Tell me. Corrections to the data matter most — accuracy is the whole point, and I'd rather you catch my mistake than inherit it. A forum thread launched me; maybe this launches you.