Tool
Headwind calculator
Why a headwind costs more than a tailwind gives back
At 25 km/h with 8 m/s (29 km/h) straight at you, you lose 4.6 minutes per 10 km. The same wind straight behind you gives back only 3.6. Out into it and home with it, you're 1.0 minutes slower than on a still day. Three things do it:
- Time is distance divided by speed. Losing 4 km/h costs more minutes than gaining 4 km/h saves, because you spend longer out there when you're slow.
- Air resistance grows with the square of the air's speed over you. Into the wind the air arrives faster, and you pay for the square. With the wind behind you, the gain is smaller than it feels.
- Riders don't bank a tailwind. You sit up, freewheel, take the corners. The app never lets a tailwind add more than 35% to your speed.
| Wind | Lost into it | Gained with it | Net over 20 km |
|---|---|---|---|
| 4 m/s (14 km/h) | +2.2 min | −1.9 min | +0.3 min |
| 6 m/s (22 km/h) | +3.4 min | −2.8 min | +0.6 min |
| 8 m/s (29 km/h) | +4.6 min | −3.6 min | +1.0 min |
| 10 m/s (36 km/h) | +6.0 min | −4.4 min | +1.6 min |
| 12 m/s (43 km/h) | +7.4 min | −5.1 min | +2.3 min |
Why the app counts a quarter of the forecast wind
A forecast's wind is the wind 10 metres above open ground. On a bike you're about a metre and a half up, among trees, houses and hedges, and often behind other riders. Velvind calibrated its clock against real recorded rides: counting a quarter (25%) of the forecast wind gave the truest arrival times; counting all of it gave the worst.
Choose “All of it (open road)” in the calculator to see the physics on a fully exposed road. At 8 m/s and 25 km/h that's +27.8 minutes into the wind and −6.2 with it. Read it as an upper bound, not an ordinary day.
What the calculator leaves out
- Climbs. The calculator times a flat road. On a climb the wind takes a smaller share off your speed, but you're out in it longer; the app times every 250 metres of your route with its own gradient.
- Gusts, and a crosswind that pushes the wheels about. Only the part of the wind along the road changes your speed.
- Drafting. Behind another rider, far less of the wind reaches you.
The app works all of this out for every 250 metres of your route: the climbs, the wind at the minute you're there, and which part of the ride is into it. Wind forecast for your bike route shows how.
Read on
Coming to the App Store.
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