How the Tailwind Atlas is calculated
We combine OpenStreetMap cycle routes with 20 years of hourly ERA5 climate data (2006–2025) and average wind, rain and temperature along each route, month by month and in both directions.
- Routes: OpenStreetMap cycle route relations of the international (EuroVelo) and national networks in Europe with at least 100 km of mapped main line, assembled by Waymarked Trails. Alternatives and branches are left out.
- A route with gaps or branches is published only if its start and end are stated explicitly — from/to tags, Wikidata, the route name, or our curated list of well-known routes (Danube, Loire à Vélo, Rhine EV15, Moselle, Weser, Oder-Neisse, Hadrian's Cycleway, EuroVelo sections…) with ends and length taken from the official route website or EuroVelo; the line between the ends follows the mapped relations, and its length must be within 15% of the official one. Loops (such as Lake Constance) are shown clockwise and anticlockwise. Sections that lie inside a whole published route are left out; routes without a name are left out.
- The line is cut into sections of about 25 km; each section uses the ERA5 grid cell (0.25°, about 25 km) over land nearest to its midpoint.
- Wind: hourly 10 m wind at 9:00–18:00 local solar time. Tailwind is the wind component in the direction of travel (negative = headwind). Route and stage values are length-weighted averages of their sections; “headwind > 15 km/h” is the share of daytime hours with at least that headwind.
- Weather: rain between 9:00 and 18:00 local solar time (riding hours) and the maximum temperature per local solar day. Rain day = at least 1 mm in riding hours. Good day = less than 1 mm in riding hours and a high between 10 and 30 °C. Best months = every month within 3 percentage points of the highest share of good days (the noise of 20 years); the best summer month is the best of June–August. Daylight is the astronomical day length in the middle of the month at the route's mean latitude. The better direction is the one with a tailwind; under 2 km/h it counts as “either”.
- Stages: routes of 400 km or more are split into stages of about 100–150 km that end at towns of 2,000 or more people within 3 km of the route.
- Limits: ERA5 slightly over-counts light-rain days and underestimates daily highs by 1–2 °C; wind in valleys, forests and on coasts differs from a 25 km grid cell. This is climate, not a forecast.
Checks: 20 randomly chosen pages were recomputed independently — hourly ERA5 read directly from the Open-Meteo open-data bucket with separate code (and spot-checked against the Open-Meteo archive API), and every page total rebuilt from its sections; the largest difference in the published monthly values was 0.5 pp / 0.05 km/h.
How to read the numbers
Wind is the 10 m wind of a 25-km grid cell, daytime hours 9:00–18:00 local solar time; at saddle height in a sheltered valley it is weaker, on a coast or ridge stronger. A positive value is a tailwind. ERA5 slightly over-counts days with ≥ 1 mm of rain (by about 5–7 percentage points) and underestimates daily highs by 1–2 °C. Good day = less than 1 mm of rain between 9:00 and 18:00 (riding hours, local solar time) and a high between 10 and 30 °C; rain at night or in the evening does not spoil it.