When to Switch to Winter Tyres: The 7°C Rule, Not the First Snow
“When should I put the winter tyres on?” has two different answers, and because people mix them up they either fit them far too early or get caught out by the first cold morning.
The first answer is the legal calendar — whatever your country or state requires. The second is the physical calendar: the point at which the rubber compound stops doing its job. They aren’t the same date, and neither of them has much to do with snow.
The physical rule: 7°C, not the first snowfall
A summer tyre’s compound begins to harden below roughly 7°C. A hardened tyre doesn’t conform to the road surface, and the result is a longer braking distance — on dry tarmac, not just ice.
So the practical rule is: winter tyres are fitted for cold, not for snow. In a mild coastal city that never sees snow, November mornings still drop below 7°C, and on those mornings a summer tyre is already the weaker choice.
The reverse matters just as much. Leaving winter tyres on into spring wears them out fast: the soft compound shreds on warm tarmac, braking distance lengthens and fuel consumption rises. Running winter tyres in summer is as wrong as running summer tyres in winter — the bill just arrives more quietly.
The decision test: if morning temperatures stay below 7°C for several days running, it’s time. Watch the thermometer, not the calendar.
The legal calendar depends on where you are
There is no single rule, and this is where drivers get caught:
| Approach | Examples | What it means |
|---|---|---|
| Fixed-date requirement | Some European countries mandate winter tyres for part of the year, often from mid-November to mid-April, sometimes only for commercial vehicles | A date, not a weather condition — you can be fined on a warm dry day |
| Situational requirement | Winter tyres required whenever conditions are wintry (ice, snow, slush) | No date to remember, but the burden is on you to judge conditions |
| No requirement | UK and much of the US | Legal, but insurers and courts still look at whether your tyres suited the conditions |
| Chain / traction laws | Mountain passes and specific routes | Applies seasonally or when posted, independent of tyre type |
🔴 Check your own jurisdiction each season, and check it again if you drive abroad. These rules change. A country that used a 1 December start may have moved it to mid-November; a fleet planning on last year’s dates will be exposed for the first fortnight of the season.
M+S isn’t the mark you want — look for 3PMSF
Two sidewall markings get treated as the same thing. They aren’t:
| Marking | What it actually means |
|---|---|
| M+S (Mud + Snow) | The manufacturer’s own declaration. No test is required, and it appears on plenty of summer and commercial tyres. |
| 3PMSF (three-peak mountain snowflake) | Tested winter performance — awarded to tyres that pass a snow traction test. |
If you want genuine winter capability, 3PMSF is the mark. M+S may satisfy an inspection in some places, but it isn’t what holds you on an icy incline.
Three checks before you fit them
1 · Tread depth. The legal minimum in most of Europe is 1.6 mm, but that is an end-of-life threshold, not a winter-performance one. Below 4 mm a winter tyre’s grip in snow and standing water drops off noticeably. Measure last season’s set before fitting: under 4 mm, it isn’t really a winter tyre any more.
2 · Age (the DOT code). Four digits on the sidewall: the first two are the week, the last two the year. 3623 means week 36 of 2023. Rubber ages in storage as well as on the road. A tyre over 10 years old should be replaced even with good tread, and winter tyres reach that point sooner because the soft compound hardens with age.
3 · Cracking and damage. Fine web-like cracks on the sidewall mean the compound is finished, whatever the tread says.
Storing the set you take off
A tyre set is an asset, and it’s easy to lose one over a single summer.
- Wash and dry them. Road salt and brake dust left on the rubber attack it.
- Mark them. Chalk the position on each tyre (NSF = near side front). Next season you’ll want to rotate them properly, and that needs to know where each one came from.
- Mounted on rims: stack flat or hang them. Unmounted: stand them upright and turn them every month or so.
- Cool, dark, dry. Sunlight and ozone (near an electric motor or generator) degrade rubber.
- If you bag them, use thick airtight bags — a loose bag traps moisture and does the opposite of what you wanted.
Are two sets really more expensive?
The common objection is cost. The arithmetic is friendlier than it looks: with two sets, each one only wears for half the year. Your total mileage is unchanged, so the sets last roughly twice as long. The genuine extra cost isn’t rubber. It’s the seasonal changeover labour and storage.
Against that sits a benefit that pays for itself in a single event: the braking distance difference on cold wet tarmac is the difference between an incident and a scare. I set out how to track vehicle costs line by line in the true cost per mile. Tyres are the most commonly mis-costed line on it, because the money goes out in one lump and the benefit arrives spread out.
If you run a fleet: a calendar, not a date
On one car this is a memory problem. On ten it’s an operations problem.
- Two weeks before the season: confirm this year’s legal dates. They move.
- Before the changeover: measure tread on every vehicle, list anything under 4 mm, and order in one batch. Once the season opens, stock tightens, prices rise and you can’t get a booking.
- Record per vehicle: which set is on it, how many seasons it has done, and its DOT code. Without that record you either pay twice for the same set or send a vehicle out on rubber that has aged out.
- Rotate at changeover. Cross-rotation happens during the same fit. It costs nothing extra.
- Chains and traction devices: on mountain routes winter tyres alone may not satisfy the requirement, and carrying chains is often checked separately.
The underlying discipline is the one I described in fleet maintenance tracking: by date OR by mileage, whichever comes first. Tyres add a third trigger — temperature.
To keep renewal dates and inspections on one calendar alongside it: the vehicle document renewal calendar. The tyre changeover is that calendar’s November line.
The whole decision reduces to one sentence: watch the thermometer, not the calendar, but don’t miss the legal date either. One protects you, the other protects your wallet.
Fuat Çakır — industrial engineer and management consultant. He works on fleet and maintenance operations in manufacturing and service businesses, and built Odovo out of that need.
If you want service and renewal dates reminded by date or mileage: Odovo — one vehicle free.
Tread depth is also on the inspection list; the full pre-test checklist is in preparing for a vehicle inspection.
Frequently Asked Questions
At what temperature should I switch to winter tyres? Around 7°C. Below that a summer tyre’s compound hardens and braking distances lengthen even on dry tarmac. The practical test is several consecutive mornings below 7°C — not the first snowfall, and not a fixed date on the calendar.
Is an M+S tyre a winter tyre? Not necessarily. M+S is a manufacturer declaration with no test behind it and appears on many summer and commercial tyres. The mark for tested winter performance is 3PMSF, the three-peak mountain snowflake symbol.
What tread depth do winter tyres need? The legal minimum in most of Europe is 1.6 mm, but that is an end-of-life limit. Winter grip in snow and standing water falls off noticeably below 4 mm, so 4 mm is the practical threshold for refitting a stored set.