Every outdoor ride
is an aero test.
Link your bike computer once, and every outdoor ride with power gets a CdA. The more you ride, the more precise it gets.
Start tracking my CdA for free Garmin · Wahoo · COROS · Hammerhead auto-sync · Checked once against a wind tunnel: 0.8% apart No device account? Upload FIT files instead · No credit card to sign upIllustration: the dashboard with your latest ride, your CdA and your next race (sample numbers)
AUTO-SYNC
Finish your ride and do nothing. Your CdA shows up on its own.
Link Garmin, Wahoo, COROS or Hammerhead once, and every outdoor ride with power is estimated automatically. Trainer and Zwift files are skipped on their own.
No device linked? Drop FIT files onto the CdA analysis page and it works the same.
CONVERGENCE
It tells you which rides to trust and which to drop.
Rides are combined, the more reliable ones count more, and the error band narrows as you ride. Rides with drafting, a flat or a sloppy position are flagged as outliers automatically, with the reason in plain words.
Your last five rides all sit around 0.24. You can plan your race on it.
Illustration: one dot per ride, band = converged CdA ± error, hollow = outlier, left out. Same bike, same position: a trend heading down is progress.
SETUP COMPARE
Is the new helmet worth it? A few rides will tell you.
Tag each ride with your gear, and setups are grouped and compared automatically, then turned into seconds for your next race.
The two error bands don't overlap. The difference is real.
Illustration: 3 to 4 rides per setup, changing one thing at a time. If the bands overlap you can't tell them apart yet; ride twice more.
RACE PLAN
When your CdA changes, your race plan tells you to recalculate.
Each plan remembers the CdA it was built on. When your converged CdA comes down, the dashboard works out the seconds first, and one tap rebuilds the six pacing levels, race-day weather and course file with the new number.
IRONMAN 70.3 Taitung
After recalculating, every segment's level and wattage follow the new CdA (Kona 226 sample calculation)
Backtest on 64 real race files: with a lookup CdA, 81% land within ±5%; with your own CdA, 86%. How the six levels, wind and weather are calculated →
Checked once against a wind tunnel: 0.8% apart.
In January 2026, an athlete we coach (8:17 full-distance finish) had their race equipment measured in the wind tunnel at the HKUST Aerodynamics and Acoustics Facility (AAF). Six months later they raced IRONMAN Hamburg. We ran the power file from that race through AeroPacer, and the engine, which never saw the wind tunnel result, solved their CdA straight from it. This is a check on one person and one race:
Note: this is an n = 1 check, not a guarantee of accuracy. The wind tunnel value is a single-point measurement at 0° yaw in a fixed position; the race estimate covers 4.3 hours of real riding, so the two were never going to match exactly. A 0.0005 difference in the assumed rolling resistance moves CdA by about 0.005, more than the gap here, so there is some luck in the 0.8%. What the data can support is this: the wind tunnel value falls inside the estimated range, close to the middle. The precision of a single estimate depends on file quality (flat, little drafting, steady cruising is best); the subscription's multi-record convergence keeps narrowing the range as data accumulates.
The guy who built this
races it too.
Lo U IanTriathlon coach · Founder of AeroPacer
Born and raised in Macau, moved to Taiwan for university and stayed. Coaching since 2016, more than 100 athletes one on one; over 20 of them have qualified for the IRONMAN World Championship and 3 have gone under 9 hours at full distance. Co-founder of the running analytics service RunningQuotient, and author of three Chinese-language books: Self-Coached Triathlon Training, The Complete Guide to Scientific Marathon Training, and Understanding Cycling Power Training Data.
He has taken athletes into a wind tunnel and knows most riders will never get inside one. AeroPacer turns that one test into data from every outdoor ride.
- IRONMAN Certified Coach
- Athletes across Taiwan, Hong Kong, Macau and China