Winter tyres: when to switch and why temperature matters more than snow

The most common mistake with winter tyres is waiting for snow. Snow has nothing to do with it: rubber responds to temperature, not precipitation, which is why “it is still dry, there is time” ends the same way every year.

The threshold is around 7 °C

Summer rubber hardens as temperature falls. A hard tread conforms worse to the microtexture of the road, and grip drops — on dry surfaces too, not only wet.

Winter rubber uses a different compound that stays flexible in the cold. But at 20 °C it is too soft: braking distances grow and the tread wears fast.

The practical trigger: a steady 7 °C in the morning is the time to switch. Not a single cold snap but a settled trend.

The logic is simple: what matters is the temperature on your coldest journeys, and that is the morning.

Rubber age matters more than tread

This is the most common non-obvious mistake when buying used.

Rubber ages by years: the compound loses flexibility and microcracks appear. A winter tyre approaching ten years old does not behave as a winter tyre, even with full tread. It has hardened — which is to say it has stopped doing the one thing it was bought for.

The manufacture date is on the sidewall as four digits: week and year.

Tread depth matters separately in winter: the legal minimum is usually below the practical one. On a winter tyre the sipes stop working long before the legal limit.

Pressures in the cold

Pressure falls by roughly 0.1 bar for every 10 degrees of cooling. So tyres inflated in autumn are under-inflated by winter.

The consequences of low pressure: longer stopping distances, worse handling, uneven wear, higher fuel consumption.

Check them cold — after a drive the tyres are hot and the readings are inflated.

Tyre pressure monitoring triggers more often in winter for exactly this reason; on an indirect system a relearn is needed after inflating — covered in the TPMS article.

A full set, not two wheels

Fitting winter tyres to the driven axle only is not economy, it is a change in how the car behaves at the limit.

Winter front, summer rear: the rear axle lets go first and the car spins.

Winter rear, summer front: the front axle will not hold and the car does not turn in.

Both are worse than a full set of summer tyres, because they are unpredictable. Mismatched tyres across axles also upset ABS and stability control — covered in the tyre size article.

What the electronics do and do not do

ABS does not shorten stopping distances on snow — it preserves steering. On loose snow, distances with ABS can even be longer, because a locked wheel builds a wedge ahead of itself.

Stability control contains a slide but does not repeal physics: with no grip there is nothing to work with.

The main conclusion: the electronics work with whatever grip the tyres provide. They do not create it.

What to watch on a scanner in winter: ABS and stability codes, which become more frequent with mismatched tyres, and the four wheel speeds in live data — a discrepancy is visible immediately.

The pre-winter procedure

1. Check the manufacture date of the winter set, not only the tread.
2. Switch by temperature, not by snow.
3. Set the pressures cold after fitting.
4. Relearn the pressure monitoring if it is indirect.
5. Read ABS codes after the swap — wheels fitted on the wrong side show up immediately.

In short

• The trigger is a steady 7 °C in the morning, not the first snow.
• A ten-year-old winter tyre does not behave as a winter tyre.
• Pressure falls with cold; check it on cold tyres.
• Two winter wheels are worse than four summer ones — the car becomes unpredictable.
• ABS preserves steering but does not create grip.

Download the app — ABS codes and all four wheel speeds are read with an ELM327 adapter over Bluetooth SPP on Android.