Reference

Glossary

CdA	Drag area: drag coefficient × frontal area, in m². The aerodynamic drag of you and your bike.
Crr	Coefficient of rolling resistance: the drag of the tyres on the road, as a fraction of weight.
ρ (rho)	Air density, in kg/m³: about 1.225 at sea level and 15 °C, lower when warm, humid or high up.
Virtual elevation (VE)	The elevation profile your power, speed and parameters imply. It matches the road when the parameters are right.
Closure	A run or loop ending at the height it started. The closure error is how far it misses.
Drivetrain loss	Power lost between the power meter and the rear tyre, in percent.
Air speed	Your speed relative to the air: ground speed plus the headwind component.
Yaw	The angle between the oncoming air and your direction of travel, caused by crosswind.
Wind exposure	How sheltered a course is, which sets how much of the 10 m wind reaches rider height.
Station pressure	The absolute air pressure where you are. Sea-level pressure is the same reading adjusted to sea level, as weather reports give it.
Baseline	The saved analysis of a ride the others are compared with.
SD, CV	Standard deviation of repeated results, and the same as a percentage of their mean (coefficient of variation).

CSV format

The first row holds the column names, in any order and any case. One row per sample, ideally one per second.

Column		Contents
`time`	Required	Elapsed time as mm:ss.s or h:mm:ss, clock time such as 2:00:00 PM, or an ISO date-time
`power`	Required	Power in watts
`speed`	Required	Ground speed in km/h
`airspeed`	Optional	Air speed in km/h, from an air speed sensor
`elevation`	Optional	Elevation in metres
`lap`	Optional	Lap number
`lat, long`	Optional	GPS coordinates in degrees

CSV files don't carry a date, so elapsed times are counted from when you upload unless the time column has full dates. Download an example CSV.

The physics

Between two consecutive samples, the energy balance gives the change in virtual elevation Δh:

m·g·Δh = η·P·Δt − Crr·m·g·v·Δt − ½·CdA·ρ·v_air·|v_air|·v·Δt − ½·m·(v² − v₀²)

m total mass, g 9.81 m/s², P power, η 1 − drivetrain loss
v and v₀ ground speed now and at the previous sample, v_air air speed (negative in a tailwind faster than you)
Summing Δh from the start gives the virtual elevation. Across joins between laps it holds level; across pauses over 10 s it follows the recorded elevation.

Fitting searches CdA (and Crr when possible) for the values that minimize the closure error or the difference from the recorded elevation.

Units

Choose metric or imperial in your profile. Everything is stored in metric and converted for display, so switching never changes a result. CdA is always in m². Air density shows in kg/m³ or lb/ft³ (1 kg/m³ = 0.0624 lb/ft³).

Data and privacy

Your activities, files and analyses are stored in your account. Only you can see them.
Weather lookups send the ride's approximate location and time to Open-Meteo. Maps load tiles from OpenStreetMap.
Deleting an activity deletes its file and analyses. See the privacy policy for details.