TyreSwitch

How TyreSwitch works

TyreSwitch suggests the best dates to change from summer to winter tyres in autumn and back to summer tyres in spring. This page explains exactly how the recommendation is calculated, which data we use, and where the limits of that approach lie. We publish these rules so you can judge the result for yourself. The recommendation is a guide; the decision is always yours.

Inputs

The calculation uses three kinds of input:

  • Your location: a town, postcode or coordinates. This decides which forecast and climate data apply.
  • Weather data: a forecast for roughly the next 10 days, and climate averages for the days beyond that.
  • Your driving profile: when you usually drive, your experience, the roads you use, how often you drive and the type of tyres fitted.

Seasons

  • Autumn (summer to winter tyres): 15 August to 31 January.
  • Spring (winter to summer tyres): 1 February to 15 June.
  • Off-season: 16 June to 14 August. No change is needed; we show the next expected window based on climate data.

Autumn rules

1. The 7 °C rule

We calculate the rolling 5-day average of the daily mean temperature and find the first day from which that average stays below 7 °C. This is the trigger day. The trigger day and the 7 days before it are labelled best. Days 8 to 21 before it are a good time. Earlier days are too early, and days after the trigger day are overdue.

2. Frost and snow

We find the first day with a minimum temperature at or below 0 °C, or with likely snow. That day and every later day are at least overdue. The best window is pulled earlier so that it ends at least 3 days before that first frost.

3. Black ice

Days with precipitation and a daily minimum temperature between −2 °C and +2 °C raise the urgency strongly and trigger an explicit black-ice warning.

4. Time of day

We use the temperature at the hours you actually drive: early morning (5–9), daytime (9–17), evening (17–22) and night (22–5). If you drive in several slots, we use the coldest. Beyond the forecast range, early morning and night slots use the average daily minimum temperature.

5. Experience

Novice drivers (less than 2 years) get a threshold of 8 °C and a window about 5 days earlier. Confident drivers get the same result as experienced drivers; the recommendation is never later than the base rule.

6. Roads

Mountain driving is treated as 1.5 °C colder, and snow is weighted more heavily. Mainly rural driving moves the window about 2 days earlier, because rural roads are usually cleared later.

7. Frequency

Occasional drivers see softer wording. The dates do not change.

8. All-season tyres

No change is needed. We show a warning only for heavy snow or regular mountain driving.

9. Workshop lead time

We suggest booking a workshop 7 to 10 days before the best window starts.

10. Forecast and climate projection

Days beyond the roughly 10-day forecast are climate-projected estimates. They can be labelled good time at most, never best.

Spring rules

Spring mirrors autumn. The 5-day average must stay above 7 °C (8 °C for novice drivers), and the best days start the day after the last frost or likely snow. The first 7 days after it warms up are best, days 8 to 21 are a good time, and after 21 days the change is overdue, because winter tyres wear quickly and brake less well in warm conditions. Novice drivers get a window about 5 days later, rural driving about 2 days later, and mountain driving is treated as 1.5 °C colder, which also moves the date later.

Legal rules are shown separately from the weather-based recommendation. They come from official and publicly available sources and are summarised in plain language on our winter tyre laws overview. Laws change, so we always recommend checking the current local rules. Nothing on TyreSwitch is legal advice.

Data sources and licences

  • Weather forecast: MET Norway Locationforecast 2.0, provided by the Norwegian Meteorological Institute under the Creative Commons Attribution 4.0 (CC BY 4.0) licence and the Norwegian Licence for Open Government Data (NLOD).
  • Climate averages: Copernicus ERA5 reanalysis. We use day-of-year mean and minimum temperatures averaged over the last 10 years on a grid of 0.25–0.5°. Contains modified Copernicus Climate Change Service information. Neither the European Commission nor ECMWF is responsible for any use of this information.
  • Geocoding: Nominatim, using data © OpenStreetMap contributors, available under the Open Database Licence (ODbL).

Location lookups and forecast requests pass through our own API, which only caches results briefly and does not store your queries. More details are in our privacy policy.

Limitations

  • Forecasts are uncertain. Accuracy decreases with each day ahead, and local effects such as valleys, coasts or urban heat can differ from the forecast point.
  • Climate averages are not forecasts. Beyond about 10 days, we can only say what is typical for the time of year, not what will actually happen in a given year.
  • Grid resolution. Climate data on a 0.25–0.5° grid smooths out small-scale differences, such as between a valley floor and a nearby hill.
  • Road conditions. We do not observe actual road surfaces, gritting or snow clearing.
  • Your car and tyres. We do not know the condition, age or tread depth of your tyres.

Disclaimer

TyreSwitch provides general information to help you plan. It is not a guarantee of road safety and not legal advice. Always adapt your driving to the actual conditions, follow official warnings, and check current local rules. For more background, read our guides on when to change to winter tyres and when to change to summer tyres, or try the calculator.