MyCdA.app
MyCdA.app estimates your aerodynamic drag area (CdA) and rolling resistance (Crr) from rides recorded with a power meter, speed sensor and cycling computer. Compare runs to find out whether a change in position or equipment makes you faster.
Try it: mycda.app (free)
Features
- Upload Garmin
.fit and .csv files, including gzipped and zipped exports. Problem files say exactly why they can't be used, and failed or interrupted uploads can be retried.
- Explore power, speed and elevation over time or distance, with laps, automatic loop detection and an OpenStreetMap view of the track.
- Analyze any lap, set of loops or range with R. Chung's virtual elevation method. Tune CdA and Crr by hand, or let Suggest CdA fit them to the recorded elevation or to loop closure.
- Air speed: use an air speed sensor (via CSV), still air, or a wind model built from hourly weather for the time and place of your ride.
- Air density from temperature, dew point, pressure and altitude, looked up from historical weather (Open-Meteo). It's also a standalone calculator.
- Compare saved analyses against a baseline in watts saved and seconds per 40 km, with the mean, standard deviation and coefficient of variation of CdA.
- Metric or imperial units, light and dark themes, and phone-friendly layouts.
How it works
| Part | Technology |
|---|
Web app (web/) | React 19, TypeScript, Vite, Mantine, React Router, TanStack Query, Plotly, Leaflet |
Analysis core (web/src/core/) | Framework-free TypeScript: virtual elevation, fitting, wind model, air density, loop detection |
| Backend | Firebase Auth, Firestore, Storage and Hosting. Cloud Functions (functions/, Node 22) parse uploads and serve activity data |
| External data | Open-Meteo (weather, elevation) and OpenStreetMap (maps), with no API keys |
Architecture, design notes and decision records are in docs/.
Development
You need Node 22+ and, for the emulator tests, Java 21+ and Chrome.
# web app
cd web
npm ci
cp .env.example .env.local # fill in your Firebase web config
npm run dev # http://localhost:5173
# or run everything locally against the Firebase emulators
npm --prefix ../tests/emulator ci
npm --prefix ../tests/emulator run emulators # terminal 1
npm run dev:emulators # terminal 2
Tests:
npm --prefix web test # analysis core, data and UI helpers (Vitest)
npm --prefix functions test # upload parsing (node --test)
npm --prefix tests/emulator test # security rules, functions end to end, browser tests (Playwright)
From the repository root, npm run dev, dev:emulators, emulators, build, lint, test (web and functions) and test:emulator forward to the packages; each package still installs its own dependencies with npm ci.
CI runs all of them on every push (.github/workflows/ci.yml).
Releasing
Bump version in web/package.json on master, then tag that commit with the same version and push the tag:
git tag v2.1.0 && git push origin v2.1.0
The Deploy workflow checks that the tag matches the version and is on master, runs CI, and deploys to Firebase. The version shows in the app's footer.
Setting up your own instance
- Create a Firebase project on the Blaze plan. Enable Email/Password sign-in, Firestore and Storage.
- Point
.firebaserc at your project, and fill in web/.env.local from the project's web app config.
- Deploy with
firebase deploy. That deploys the Firestore and Storage rules, the functions, and hosting (which builds web/ first).
CSV format
The header row needs time, power and speed (km/h). It can also have airspeed, elevation, lap, lat and long. See the FAQ for details, or download the example file.
Community
Questions and release notes: the MyCdA community. Bugs and ideas: GitHub issues.
License
MIT
