When to change? What the measurements say — and what the rule of thumb is worth

The Rule of Thumb and Its Origin

The TCS formulates it as follows: "The rule of thumb is 'from O to O,' meaning from October to Easter, you should drive with winter tires. However, if regional weather conditions require it, you should mount them earlier or switch back to summer tires later."[1]

The second sentence is the more important one, and it is almost always omitted. The rule is a calendar trick, not a law of nature — it describes the Swiss Plateau in an average year.

In Switzerland, there is no mandatory winter tire law. The TCS states: "In Switzerland, there is no legal obligation to equip your car with winter tires in winter."[2] No date forces you to do anything, and none prohibits you from doing anything.

What the law does require is something different: a roadworthy vehicle (Art. 29 SVG) and the ability to control it at all times (Art. 31 Para. 1 SVG).[3] The TCS concludes from this: "Driving with summer tires in winter conditions, whether with a car, camper van, or caravan, is not considered roadworthy and is therefore punishable."[4]

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The 7-Degree Rule — and Why It Is Too Strictly Formulated

Everywhere it says: "Switch to winter tires below 7 degrees." We also had this in several places until we looked up the measurements behind it.

The TCS measures on a wet road at exactly 7 °C asphalt temperature, full braking from 80 km/h, in dimension 205/55 R16:[5]

Read the numbers again. At exactly 7 degrees, the summer tire is 5.5 meters worse than the winter tire — it is not yet at an advantage there, but clearly at a disadvantage.

The point at which the summer compound performs better is somewhere above that, and it also depends on whether it is wet or dry. On dry asphalt at 30 degrees, the summer tire predictably brakes best.

As a rule of thumb, "winter tires below 7 degrees" is fine. As a threshold value with an equal sign, it is not — it underestimates the winter tire in the transition zone. And two subtleties are involved: It's the asphalt temperature, not the air temperature, and at seven in the morning, the asphalt is colder than what the thermometer in the car shows.

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And on Snow?

There, the difference is no longer a matter of dispute. The TCS measures at minus 3 °C on snow, braking from 50 km/h: "A summer tire has no place on snow. With it, the car stops 27 m later — about eight car lengths — than with a winter tire."[6]

From 50 km/h. That's 50 km/h in a village, not on the highway.

These numbers are TCS measurements, not ours — we do not operate a test stand. They apply to the stated conditions, the stated dimension, and the best tire in each test, not as an average across all models.

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So When to Switch?

From what is proven, a workable procedure emerges.

To Winter Tires: Rather Early

The calendar says October. The weather can say earlier. Those who drive over a mountain pass to work or live at higher altitudes should go by the mountain route, not the lowlands.

The disadvantage of an early change is small: A winter tire at 12 degrees dry brakes slightly worse than a summer tire and wears out slightly faster. The disadvantage of a late change is the first snowfall that you didn't order.

A practical trigger instead of a date: When there is frost on the car in the morning, the time is right.

To Summer Tires: Rather Late

The calendar says Easter — which fluctuates between March 22 and April 25, making the rule inherently imprecise. Rather wait for stable nights above zero degrees than for a date.

The disadvantage of a late change is manageable: A winter tire at 18 degrees wears out noticeably faster. The disadvantage of an early change is the April snow, which occurs somewhere in Switzerland every year.

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Not Just Changing — But Also Looking

The wheel change is the only opportunity in the year when someone holds each tire individually. Use it:

Measure tread depth. Legally, 1.6 millimeters are required — Art. 58 Para. 4 VTS: "Tires must have tread grooves at least 1.6 mm deep across the entire tread surface."[7] Below that, it costs 100 Swiss francs per tire.[7]

The TCS recommends significantly more: "The TCS continues to recommend replacing winter tires for driving safety with a tread depth of less than 4 mm and summer tires with a tread depth of 3 mm."[8]

Calculate one season ahead. A winter tire with 4.5 millimeters in April will be around 4 in November — and then already at the recommendation limit. Storing it means buying new ones in the fall. Doing it right away saves an appointment.

Check age. The DOT number on the sidewall indicates the week and year — how to read it.

Note the position and swap them next time. Then all four will wear evenly, instead of two in front wearing twice as fast.

And then store them correctly — that also determines how the set survives the six months.

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What About All-Season Tires?

Then the change is omitted — and with it, the annual check. That's the silent disadvantage no one mentions: Those who never change their tires never see them up close.

Set a reminder for yourself twice a year, in October and April: Measure tread, inspect sidewalls, check tire pressure. Ten minutes that the wheel change would otherwise have taken care of.

Whether all-season tires are suitable for your driving situation and what the legal situation is, can be found in our article All-Season Tires and the Law.

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The Four Sentences to Take Away

1. "From O to O" is a rule of thumb for the Swiss Plateau, not a law — and the TCS itself says that regional weather takes precedence.
2. At exactly 7 degrees and wet, the winter tire is still 5.5 meters better. The threshold is higher than the rule claims.
3. On snow, it's 27 meters from 50 km/h. There's nothing to weigh there.
4. The change date is the best inspection date — tread, age, sidewall, position.

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For further reading: How to recognize a real winter tire · Storing tires correctly · Winter tires in our assortment

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