Estimated reading: 4 minutes

aerosensor testing

Aerosensor settings

Basic settings

To function correctly, Aerosensor requires the following inputs, entered in the ConnectIQ app here:
Menu → Aerosensor settings → Basic settings:

Aerosensor calibration

Calibration is reported for every run and depends on bike setup. Minor changes (helmet, wheels) have little effect, but adjustments to handlebar height, reach, or sensor position can significantly impact results.

Begin each session with 2 runs and compare reported calibration to the current setting.
If it differs by more than 5%, update it before continuing.

Total mass

Mass affects acceleration, gravity, and rolling resistance, making it critical for accuracy.

Weigh yourself before each session, including bike, gear, and accessories.
Carry fluids on the bike so total weight remains consistent as you drink.
If you refill bottles or use the loo, re-weigh before continuing.

Wheel circumference

Measure the circumference of only the wheel with the speed sensor. This depends on tires, wheels, pressure, and system weight. To measure:

Align a piece of tape on the wheel and ground.
Sit on the bike and roll forward one full revolution.
Mark the new ground position and measure the distance between marks.

Reference Crr (Coefficient of Rolling Resistance)

Find Crr values for your tires and pressure at: https://www.bicyclerollingresistance.com/

Crr depends on road roughness but has a small, consistent effect on CdA measurements.
If testing on a velodrome (wood track), reduce Crr by ~40%.
Example: A road Crr of 0.0035 should be 0.002 on a velodrome.

If unsure the following table shows some typical values for smooth tarmac.

Tyre Type	Tyre pressure
Tyre Type	60psi	80psi	100psi	120psi
CLINCHER: TT	0.0044	0.0037	0.0033	0.0030
CLINCHER: ALL-ROUNDER	0.0056	0.0047	0.0042	0.0040
CLINCHER: ALL-WEATHER	0.0072	0.0061	0.0055	0.0052
TUBELESS: TT	0.0033	0.0028	0.0026	0.0024
TUBELESS: ALL-ROUNDER	0.0049	0.0042	0.0037	0.0035
TUBELESS: ALL-WEATHER	0.0057	0.0050	0.0044	0.0041
TUBULAR	0.0053	0.0046	0.0042	0.0039

Advanced Settings

These are settings that you are likely to change less frequently, but nevertheless important. You can find them in the CIQ app here:
Menu → Aerosensor settings → Advanced settings:

Power Meter Scaling

Some power is lost in the drivetrain due to friction (chain, bearings, derailleur, etc.).

Pedal, crank-arm, or spider-based power meters → Set to 0.98 (accounts for ~2% drivetrain loss).
Hub-based power meters → Set to 1.00 (measures power directly at the wheel).

CTF Calibration Offset

For SRM PM7 and older power meters only. Enter the calibration value displayed on your Garmin after calibration (typically ~520).

Time Averaging Period

CdA (not CdA lap) is a rolling average over this time period. It does not affect lap values (e.g., out-back or track testing).

Recommended: 30 seconds (default).

Valid Brake Deceleration

AeroSensor automatically starts a new lap when braking to exclude braking forces from calculations.

Default: 1 m/s²
If using Aerodrome lap trigger: set to 10 m/s² to avoid inadvertently triggering laps for example when going up banking after last lap.

Valid Speed Min

Laps start automatically when speed rises above this threshold.

When testing without Aerodrome lap trigger, set it just below target test speed.
Why? Power meters and speed sensors have small time offsets, which can introduce drag measurement errors if accelerating hard through a low threshold.
Hysteresis: Once speed exceeds the threshold, Aerosensor will not trigger another lap unless speed drops 1 m/s (3.6 km/h) below it.

Braking Time Offset

When braking, Aerosensor discards the last N seconds of data to prevent braking forces from affecting lap CdA calculations.

Recommended: 5 seconds (default).