Measuring a Segment's Wind Sensitivity
Two segments with the same length and bearing can behave completely differently — hedges, treelines, embankments and buildings all have a say.
What sensitivity means
The sensitivity factor describes how much of the calculated wind effect actually shows up. A value of 0.5 means only half the expected effect appears, because the segment is sheltered. 1.3 means the effect is stronger than calculated, typically on open embankments or exposed farm tracks.
- 0.5 to 0.8: sheltered — woodland, buildings, sunken lanes
- 0.9 to 1.1: average exposure
- 1.2 to 1.5: open fields, embankment, coastal
Deriving it from your own rides
Collect at least five to eight of your own rides on the segment with the matching wind values. Plot time deviation from the mean against the effective wind component and take the slope of that relationship. Compare it with the slope the physics model expects — the ratio is your sensitivity.
Why it helps so much
A learned sensitivity factor corrects systematic errors in wind height, shelter and segment geometry all at once. In practice it is the single most effective step from rough predictions to usable ones.
Watch for confounders
If all your fast rides happened in summer and the slow ones in winter, you are mixing form and temperature into the wind factor. Use rides from a comparable form phase, or account for temperature and surface separately.
In short
Learn the wind factor from your own rides — no model knows your segment better than your history does.
Frequently asked questions
How many rides do I need?
From five rides in different wind conditions the value becomes roughly usable; from ten it becomes stable.
Does sensitivity change?
Yes, seasonally. A maize field in August shelters differently from a harvested field in November.