What it does
Winter tyres are made from rubber that stays soft in the cold, with grooves and slits that bite into snow. This tool checks a set of tyres in four quick steps: which mark is on the sidewall, how deep the tread is, how old the tyres are and whether you have checked the pressure when cold. Then it gives one verdict: Ready, Check these or Not ready, and lists the reasons.
It also shows the winter tyre rules for Canada, the USA and the UK as we last checked them. Find the age with tyre age, measure the grooves with tread depth, and fix the pressure with tyre pressure.
How to use it
- Pick your country.
- Tap the mark you find on the sidewall: the mountain snowflake, M+S only, or neither.
- Type the tread depth in the main groove, and the date code if you know it.
- Tick the box once you have checked the pressure with cold tyres.
- Read the verdict and fix any red or amber line.
What each setting does
- Mountain snowflake (3PMSF): the tyre passed a snow grip test. This is the best mark for winter.
- M+S: the maker says it is for mud and snow. There is no grip test, and many all-season tyres carry it.
- Tread: winter tyres want 4 mm (5/32 inch) or more. Below that, snow grip drops sharply.
- Age: from the date code. Over 6 years, have them checked; at 10, replace them.
- Pressure: cold air makes pressure fall, about 1 psi for every 5 to 6 degrees C.
Worked example
Snowflake mark, 6 mm tread, made 3 years ago and pressure checked: Ready. The same car with M+S only and 3 mm tread: Not ready, because the tread is under 4 mm and the mark is a weaker one.
FAQs
What is the 7 degrees rule? Below about 7 C, winter-rated tyres grip better than summer ones even on dry roads, because the rubber stays soft. It is a guide, not a law of nature.
Are all-season tyres winter tyres? Not unless they carry the snowflake mark. M+S alone is not a snow test.
Do I need four winter tyres? Fit all four. Two winter and two summer tyres can make the car slide.
Not safety advice. When in doubt, ask a tyre shop.
Where the numbers come from
- Rules as checked November 2026 (check the official source for your area): Quebec requires winter tyres on passenger vehicles from 1 December to 15 March; British Columbia requires winter tyres (M+S or the three-peak mountain snowflake mark) on many highways from 1 October to 31 March, some to 30 April; Ontario has no law but insurers must offer a winter-tyre discount; the UK has no winter tyre law; most US states have none, though some areas ask for chains or snow-rated tyres in storms. The 7 C guide is the common tyre-safety rule: below about 7 C, winter-rated rubber stays softer and grips better. Winter-tyre tread floor of 4 mm (5/32 inch) is common tyre-safety guidance. Cold air drops tyre pressure by about 1 psi for every 5 to 6 C, from the ideal gas law. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-12.