About

I'm Ger, and I build my own bicycle wheels. Not for a living. I do it for the same reason I handle 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. It gives you exact spoke lengths, tension read off whatever tensiometer you own, and a truing simulator, with an open hub and rim database behind it. Free, no login, runs entirely 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 humbled me. The second one less so. I've hand-built fourteen-plus wheelsets since: folders, hardcore enduro, gravel, fatbikes, 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 to calculate and build a wheel without hopping between half a dozen tools: 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, plus the things I always wished it had: 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, so always re-measure.
• Code: MIT, open.

How the numbers are made

Spoke length is pure 3D trigonometry, no approximations, and the formula and the intermediate values are shown so you can check the math yourself. Tension conversions come from each tensiometer's own published table, verified against the manufacturer source where one exists. Those 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 or tensiometer? Tell me. Corrections to the data matter most: accuracy is the whole point, and I'd rather you catch my mistake than the next builder inherit it. A forum thread got me into this. Maybe this gets you in.