Winter tyres have technical and constructional features that make them suitable for use on snow- or mud-covered surfaces, and when the bitumen is especially cold, guaranteeing better grip on slippery and wet surfaces.
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Winter tyres: when and why?
Winter tyres are recommended when the temperature falls below 7°C. This is in fact the temperature at which summer tyre treads tend to harden, causing a considerable decline in performance, comfort and driving safety.
The specific compound used for winter tyres, however, ensures flexibility at such temperatures, thus guaranteeing perfect contact with the ground at all times.
When outside temperatures are almost constantly above 15°C, summer tyres should be put back on again; in this case, using winter tyres would not cause any problems, however they would tend to wear more than summer tyres. For wet, snow-covered or even icy roads, the features of winter tyres become fundamental for safe driving. At low temperatures, winter tyres reduce braking distance by 10% in the wet and 20% on snow.
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One example: on a snow-covered road, an average sized car equipped with ABS and travelling at a speed of 40 km/h when using winter tyres comes to a stop in around 30 metres, while the same car, fitted with summer tyres (if new) covers at least twice the distance before stopping.
Yet even in the rain the safety margins guaranteed by winter tyres are far superior: if needing to brake suddenly at 80 km/h, the braking distance for a car with winter tyres is around 15% shorter.
Winter tyres therefore ensure safe driving in autumn and winter, as they can face any road conditions without requiring chains. In addition, alternating summer and winter tyres significantly extends tyre life.
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Winter tyres: identification
The M+S symbol stands for MUD & SNOW, and is the symbol that legally identifies tyres with higher performance in the snow than summer tyres. This is placed on winter tyres, as well as on many all-season and off-road tyres. The symbol is placed on tyres that comply with certain requirements in terms of tread dimensions / features, without however needing to pass any special tests.
The peaked mountain with snowflake symbol, on the other hand, identifies winter tyres with suitable performance in severe snow conditions; these must be very heavily siped and be made using compounds and materials that pass strict international tests.
Winter tyres: four wheel drive vehicles
One quite common misconception is that four wheel drive vehicles don’t need winter tyres. While on one hand a 4x4 guarantees better traction than a 4x2, above all when starting from a standstill, on the other it offers no advantage when braking or performing an emergency manoeuvre (the main trade magazines are trying to help convey this fundamental concept).
For SUVs especially, the higher inertia due to the extra weight and higher centre of gravity makes situations such as an icy descent or cornering on snow-covered surfaces even trickier.
Winter tyres: which types are allowed
All tyre sizes specified on the car’s registration certificate, while if there are special sizes reserved for winter tyres these are considered additional alternatives and not restrictions. When choosing a winter tyre, drivers need to consider the most common situations they will face: as a general rule, on snow-covered roads the narrower the tread, the more grip the tyre will provide.
For winter tyres, the speed rating (maximum) can be lower than the limit specified for the vehicle, however never less than Q (=160 km/h). In this case, the new maximum speed limit must be highlighted inside the car, in a position that is clearly visible to the driver, for example a sticker on the steering wheel or on the dashboard. The main speed ratings are:
• Q: up to 160 km/h
• R: up to 170 km/h
• S: up to 180 km/h
• T: up to 190 km/h
• H: up to 210 km/h
• V: up to 240 km/h
• ZR: over 240 km/h
Vehicles should always be fitted with a full set of winter tyres. No matter what type of car you drive, the fitment of only two winter tyres will seriously affect the safety and handling of the vehicle.
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Winter tyres: technical features
A winter tyre differs from other types of tyres due to the following features:
• Softer or thermal compound, rich in silica, which provides good grip even at low temperatures. Unlike other types of tyres, winter tyres reach their optimum operating temperature much more easily and quickly, while the tread blocks remain more elastic, ensuring adequate friction even on very cold surfaces.
• Heavily siped tread and specific patterns: grip on snow- or mud-covered surfaces is provided by the more complex block pattern; moreover, the siping in the tread fills with snow and, as the snow-snow bond is stronger than the rubber-snow bond, this improves road grip.
The high empty-full ratio ensured by the number, depth and width of the tread grooves also helps discharge large amounts of water, thus improving resistance to aquaplaning.
Winter tyres: legislation
Currently there is no common Europe-wide legislation on the requirement to fit winter tyres. Consequently, specific information is needed for the countries drivers intend to travel through.
Here are details on the main regulations regarding the use of winter tyres in Europe.
For the purpose of improving road safety, traffic and mobility, in Italy the organisations that own and/or operate the road network can issue specific regulations requiring winter tyres or chains aboard vehicles for certain periods (generally from
mid-October/early November to mid-March/early April).
For further information and an updated list of such regulations, see the “Pneumatici sotto controllo” website.
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In Germany, cars must be fitted with tyres that are suitable for the weather conditions, so as to not represent a traffic hazard. On snow- or ice-covered roads, cars must be equipped for winter, meaning snow tyres and antifreeze in the windscreen washer fluid. Sanctions apply to drivers who fail to comply with such requirements. If a vehicle with unsuitable tyres then causes an accident, the driver will also face consequences with regard to his/her comprehensive insurance coverage.
In Austria, from 1 November to 15 April, vehicles weighing less than 3.5 tonnes are allowed to drive in winter conditions, i.e. snow, ice and wet snow, only when four winter tyres are fitted or snow chains are kept aboard the car and are fitted on the drive wheels when needed. Car M+S tyres must have a minimum tread depth of 4 mm. Snow chains are only allowed as alternatives when the road surface is entirely covered by snow or ice and when these do not damage the road surface. Fines for failing to comply with these rules range from 35 euros to confiscation of the vehicle.
In Switzerland, when "chains are compulsory" signs are shown, vehicles must be fitted with chains on at least two drive wheels, or alternatively snow tyres. Very heavy sanctions apply in the event of accidents caused by vehicles with "unsuitable" tyres.
In France, vehicles travelling on snow-covered roads must be fitted with snow chains when special signs are displayed indicating such requirement (commonly in mountain areas).
In Slovenia, from 15 November to 15 March, as well as at any other time when driving conditions are made dangerous by snowfall or ice, passenger cars and vehicles less than 3.5 tonnes in weight must be fitted with snow tyres on all four wheels, or alternatively, normal tyres and snow chains aboard the vehicle. In both cases, the minimum tread depth allowed is 3 mm. Vehicles weighing more than 3.5 tonnes must be fitted with snow tyres at least on the drive wheels or have snow chains aboard if normal tyres are fitted. This rule also applies to foreign-registered vehicles.
In Croatia, snow tyres or chains aboard are recommended from the start of November until the end of April; chains are required when indicated by special signs.
Poland, the Czech Republic and Greece do not have any specific requirements, however winter tyres are advisable, especially in the first two countries.