kolko7 How kolko7 decides
kolko7 looks at the weather where the car is and at the winter-tyre rules of the country or region, and turns both into one piece of advice: not yet, soon, or now.
Temperature
For every day we compute the average temperature of the 7 days before it. Once that 7-day average has been below the threshold on 3 consecutive days, winter tyres are due. The threshold is 7 °C in most places, the rule of thumb used by tyre makers and automobile clubs; where winter conditions are the norm a lower threshold is used. We look at the last 7 days and at the next 10 days of the forecast.
Frost and snow
A single night at or below 0 °C, or a single day with snowfall, in the last 7 days or in the 10-day forecast, is enough to call for winter tyres, even when the average is still mild.
The law
Some countries and regions require winter tyres during a fixed period of the year (mandatory), others only when roads are wintry (situational), others not at all. A mandatory period sets the swap date at the latest; a situational period that is in force is listed as a reason. All-season tyres with the 3PMSF (snowflake) marking count as winter tyres where the law accepts them. Rules marked “not yet verified” were compiled from public sources and not yet checked by us against the official texts.
Back to summer tyres
With winter tyres on, we advise swapping back only while the days are getting longer where the car is, once the last 14 days had no night below 5 °C and an average above 12 °C, and the 10-day forecast has no night below 5 °C, no frost and no week averaging below the threshold. Any mandatory winter-tyre period must be over, too. A warm spell in autumn never brings the summer tyres back.
Booking a garage
The swap date is the first day on which one of the conditions above is met. Garages are busy in autumn, so we suggest booking a number of days before it: 10 by default, adjustable for each vehicle. “Soon” means the swap date falls within the next 10 days; “now” means it has been reached.
Where the data comes from
Weather observations and forecasts come from Open-Meteo for the place and its elevation. Place search uses the Open-Meteo geocoding service with data from GeoNames. Every check is computed when you ask for it; nothing about an anonymous check is stored.
This is advice, not legal counsel: the driver remains responsible for tyres suited to the conditions and for the rules where they drive.
Weather data by Open-Meteo.com (CC BY 4.0). Place search by Open-Meteo.com, data from GeoNames (CC BY 4.0).