Track-day conditions, anywhere. A single-file web app that scores how good
conditions are for karting at any circuit or location — grip, lap-time pace and
comfort rolled into one X/10, wrapped in a live, time-of-day sky.
Inspired by the aesthetic of Kathy Zhou's sunset predictor, rebuilt for motorsport.
- Track-day score (0–10) — blends track grip (rain/temp dominant), lap-time
pace (cold dense air = fast) and comfort into one number, with a tagline
(
send it,grip city,wet line, …) and a plain-language "why". - Density-altitude + jetting guide — relative air density %, richer/leaner direction vs ISA baseline, and density altitude — turns the weather into 2-stroke engine tuning. Plus track-temp estimate, tyre-pressure nudge and the best session window today.
- Dynamic sky backdrop — gradient follows the track's local time (night/dawn/day/golden/dusk), tinted by cloud, rain and temperature. Contrast flips automatically; clouds drift faster in wind; rain streaks; stars at night.
- Information design — context subtag surfaces the limiting factor, a rain timeline ("dry until 14:00"), wind-direction arrow, categorical precip, and a forecast-confidence fade on the trends graph.
- Weather details drop-up — real temp + feels-like, humidity, cloud, wind, gusts, precip, pressure, a grip/pace/comfort breakdown and dry-vs-wet line.
- Search — type-ahead (Photon/OSM), grouped tracks-first then places (both
collapsible), kart circuits ranked first; accepts
lat, lon; plus a map view. - History & forecast — 60-day timeline + an SVG trends chart; an hour scrubber to check any hour of any day; next strong day finder + notify.
- Compare two tracks side by side · shareable deep links · 8 languages (auto + saved) · °C/°F & km/h/mph · installable PWA, works offline.
- Quick switch — click the track name for recents, featured, near-me, share.
- Countdown — time to the day's next peak-grip window.
All free, no API keys:
| Purpose | Source |
|---|---|
| Weather (current + daily, history + forecast) | Open-Meteo |
| Type-ahead geocoding | Photon (OSM) |
| Nearby / map circuits | Overpass API (sport=karting, highway=raceway) |
| Map tiles | CARTO dark + OpenStreetMap |
GripCast is now a Vite + TypeScript + Svelte app.
npm install
npm run dev # http://localhost:4561
npm run build # static bundle in dist/
npm run preview # serve the built bundleThe original single-file prototype is preserved at
legacy/gripcast.html for reference.
src/
lib/ score, sky, weather, geo, i18n, units, stores (typed logic)
components/ Fx, Clouds, MapView, TrendsGraph, SearchModal
App.svelte orchestration + sky/clock/popups
MIT — see LICENSE.