How are headwind, crosswind and tailwind worked out?
Updated
For each stretch, Windline compares the wind direction with the direction of the road. Wind within 60° of straight ahead is a headwind, within 60° of straight behind is a tailwind, and anything between is a crosswind. Winding stretches count as crosswind.
Stretch by stretch
Windline cuts the route into stretches of up to 5 km (3 miles) and works out which way the road runs on each one. It then reads the forecast wind for that stretch at the time you’ll ride it.
| Wind on the stretch | Called |
|---|---|
| Under 6 km/h (4 mph) | Calm |
| Coming from within 60° of straight ahead | Headwind |
| Coming from within 60° of straight behind | Tailwind |
| Anything in between | Crosswind |
| On a stretch that winds a lot | Crosswind |
The day page shows the share of the ride in each, as a Head, Cross, Tail and Calm bar.
How much harder or easier
The headline number on a day is the average headwind (or tailwind) along the route: the part of the wind pushing straight against you or straight behind you.
For the rating, Windline goes further and works out the effort. It uses a standard road-cycling model: a rider and bike of 85 kg (187 lb), rolling resistance, air drag and the slope of each stretch. Wind near the ground is slower than the 10 m (33 ft) forecast, so Windline uses about two-thirds of it at riding height. The result is how much more or less work the whole ride takes at the planned pace than it would in still air.
Side-on gusts
Gusts are checked separately, because a strong gust from the side can push a rider across the road even when the average wind is moderate. Windline takes the side-on part of each gust and allows for the gust direction swinging 20° either way. See the limits in what Good, Fair and Tough mean.