Bicycle planning · browser-local drivetrain ratios · 2026 · Solo — product framing, test-first ratio logic, interaction design, accessibility, responsive verification, production deployment
Chainline
A drivetrain drafting instrument that separates genuinely useful gear steps from differently named versions of almost the same ratio.
The problem
Cyclists and independent mechanics considering a drivetrain change often compare tooth counts in a table, then calculate rollout or cadence speed separately. That makes differently named combinations look like additional gears even when their effective ratios are nearly identical, and it separates the ratio being discussed from the wheel circumference that makes it useful. Chainline keeps that bounded planning step causal: enter up to three chainrings and fourteen cassette sprockets, set measured wheel circumference and a reference cadence, inspect every crossing on one low-to-high development ladder, mark adjacent ratios inside a transparent overlap threshold, select one gear, and copy its exact planning card. It performs deterministic ratio arithmetic only and does not verify derailleur capacity, chain length, frame clearance, chainline, component compatibility, loaded tyre rollout, installation safety, or riding suitability; every part and fit must be checked on the actual bicycle. Inputs stay in ephemeral browser state, with no account, persistence, paid API, credential, tracking SDK, outbound email, advertising, payment, or destructive operation. Production deployment dpl_AowZ74eAnnY3r8HswcZEZR3xmgDp reached READY before independent Foundry artifact, HTTPS deploy, and eight-step behavior checks passed at the stable alias.
Architecture
Key decisions
Plot effective ground instead of hardware order
Every chainring/cog crossing is sorted by development rather than cassette position. Differently named combinations therefore meet on the same axis when they cover the same distance per crank revolution.
Make overlap transparent and adjustable
An adjacent step is marked only when its percentage gain is at or below the visible one-to-eight-percent threshold. The tool calls this an overlap, not a recommendation to remove a gear.
Keep component claims narrow
Chainline calculates ratios from entered dimensions only. It repeatedly excludes capacity, chain length, clearance, compatibility, installation, tyre deformation, and riding suitability from its claim.
Use an original repair-manual instrument
Ruled paper, a bottle-green calculation field, vermilion actions, acid overlap halos, ochre and blue ring lanes, Georgia hierarchy, narrow controls, and monospaced evidence produce a Configure bench without gradients, blur, feature tiles, icon toppers, center stacking, or ornamental metrics.
Let failed gates harden the release
A circular inherited lint config, a sixteen-worker host abort, current dependency advisories, and an incorrect responsive-probe option all failed honestly before narrow repairs and complete reruns.