MyCdA

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What's your CdA?

Your aerodynamics field testing companion.

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October 2026

MyCdA is back

MyCdA has been rebuilt from the ground up. Your account, rides and saved analyses are all still here, and there's a lot that's new, much of it suggested by riders who field test every week.

Rebuilt

  • A faster, modern app that works on phones, with a dark theme
  • Maps from OpenStreetMap, and weather and air density lookups from Open-Meteo
  • A new file reader: more FIT files, .fit.gz and Garmin zip downloads, and a retry button for old uploads that failed
  • Corrected physics: pauses, gaps and lap joins no longer distort the virtual elevation

New since the relaunch

Tests table

Every out and back test of a ride, paired automatically, fitted and saved in one go.

Joined runs

Analyze the out and back legs of a test as one run, held level at the turnaround.

Opens already fitted

New analyses start at the CdA that closes the run, with a warning when no plausible value does.

Ride settings and notes

Mass, air density, Crr and drivetrain loss per ride, for when you tested another bike or kit.

Wind

Weather or your own wind, scaled to rider height for how sheltered the course is.

Air density

Look up the ride's weather, or enter station pressure or humidity.

Find your rides

New uploads at the top, sorting by ride date or name, and search across names and notes.

User guide

From collecting good data to telling real differences from noise.

Read the user guide

Ideas or problems? Tell us in the user community.

Upload

Upload rides as Garmin .FIT or .CSV files. Explore power, speed and elevation for the whole ride, a selection or individual laps.

Analyze

Pick laps or a range, then estimate your drag area (CdA) and rolling resistance (Crr) with the virtual elevation method.

Compare

Compare CdA and Crr across runs against a baseline, in watts saved and seconds per 40 km.