CdA Wind DataField - Real-time aerodynamic drag Calculate your CdA live while you ride using only a power meter and GPS. No wind tunnel, no expensive add-ons. The large wind arrow shows wind direction relative to your heading at a glance. Wind speed, air density, temperature, humidity, and pressure are displayed on screen and recorded to your FIT file every second. CRITICAL SETUP FOR ACCURACY The CdA calculation is highly sensitive to your input settings. You must set these accurately in the Garmin Connect app for the math to work: • Rider Mass (kg): Your actual body weight. • Bike Mass (kg): Bike weight + kit + full water bottles + saddlebag. A 1 kg error shifts CdA by ~0.003 m². • Rolling Resistance (Crr): Defines tire friction. Use 0.003 (Track), 0.0035 (TT), 0.004 (Good Road), 0.005 (Gravel), or 0.006 (MTB). You can also enter a custom Crr. If this is wrong, the app will miscalculate how much power is lost to the road, skewing your CdA. HOW IT WORKS CdA is derived from the power balance equation: P_aero = (Power x 0.97) - P_rolling - P_gravity - P_accel CdA = P_aero / (0.5 x rho x Va^2 x V_ground) • rho: Air density (calculated via Magnus formula using live temp, humidity, and pressure). • Va: Apparent airspeed (vector sum of ground speed + wind). • P_gravity: Slope power from barometric altitude delta. • P_accel: Acceleration power (smoothed via EMA). Result is smoothed over a 30-second rolling window. Values outside 0.10-1.00 m² are discarded. CdA is computed only when speed is above 3 m/s, power above per 30 W, and there is no hard acceleration or braking. When conditions are not met, the display shows "CdA ---", and FIT recording is paused to keep your average CdA accurate. WEATHER PROVIDERS & DATA Accurate wind data is crucial. The app pulls live wind speed, wind direction, temperature, humidity, and pressure based on your GPS location. • Garmin Connect (API Live): Pulls from the nearest weather station via your phone. Fast, reliable, no API key needed. • Open-Meteo & wttr.in: Excellent free services. Provide high-res forecast models. No API key needed. • OpenWeatherMap, WeatherAPI, Visual Crossing, Tomorrow.io: Require a free API key entered in settings. Excellent for hyper-local accuracy. Update Interval: Set to 30 / 60 / 120 / 180 min. Fallback system: When "Use Fallback APIs on Error" is enabled, providers are tried in sequence until one succeeds. Free providers are tried first to save your API keys. READING THE DISPLAY 6 Dynamic Layouts available in settings (Main Display Mode): • Carousel / Classic Split: Huge arrow pointing to the wind source (12 o'clock = direct headwind). • Wind / CdA: Huge readable numbers, easily visible at 40+ km/h. • Top Carousel: Cycles through Temp, Humidity, Pressure, Density, and Relative Wind (Head/Tail) every 2 seconds. POST-RIDE ANALYSIS All metrics recorded as custom FIT developer fields, visible in Garmin Connect charts: cda_m2, wind_speed_ms, wind_bearing_deg, wind_relative_ms, air_density_kgm3, ambient_pressure_hpa, temperature_c, humidity_pct. Open the FIT file in WKO5, GoldenCheetah, or intervals.icu for deeper analysis! TIPS • Ride flat or gently rolling roads for stable readings. • Allow ~15 sec after a position change for the 30s buffer to reflect the new CdA. • Higher speeds give a much better aerodynamic signal (aim for 30+ km/h).

Improved & bugs fixed