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1st November - Remember the Mountain Law

Each year from the 1st November till 31st March, the ‘Mountain Law’ comes into effect on roads in 34 French departments – these are mainly in mountainous areas (Alps, Massif Central,Vosges, Jura, Pyrenees and Corsica) as shown below. Under this law vehicles using the department roads must be equipped with either special tyres or snow chains/ socks. The special equipment authorised is either 4 "Winter" or "All-Season" tyres, marked M+S or 3PMSF (the M+S marking alone however is not subject to an efficiency check & will no longer be allowed from November 1, 2024), or a set of snow chains, or a set of snow socks.

The French motoring magazine ‘L’Automobile’ carried out a survey on snow covered roads to measure and compare the traction, braking and cornering /safety performances of these different tyres (All-season & Winter tyres), as well as two types of special equipment (hybrid snow socks and composite snow chains). They carried out 4 tests with the following results:

1) Accelerate from 0 to 40 km/h on the flat

  • Winter tyres: 7.3 sec

  • All-season tyres: 8.1 sec

  • Composite chains: 6.9 sec

  • Socks: 6.3 sec

2) Starting on a slope, 7% & 20%

Slope 7%

  • Winter tyres: easy starting

  • All-season tyres: impossible to start

  • Composite chains: easy to start

  • Socks: easy start

20% slope

  • Winter tyres quite easy to start

  • All-season tyres: impossible to start

  • Composite chains: quite easy to start

  • Socks: quite easy to start

3) Braking at 50 km/hr

  • Winter tyres: 25 m

  • All-season tyres: 32 m

  • Composite chains: 26 m

  • Socks: 27 m

4) Cornering a radius of 11 m & a radius of 20.5 m

Radius 11 m

  • Winter tyres: 26 km/h

  • All-season tyres: 20 km/h

  • Composite chains: 26 km/h

  • Socks: 27 km/h

Radius 20.5m

  • Winter tyres: 33 km/h

  • All-season tyres: 26 km/h

  • Composite chains: 34 km/h

  • Socks: 34 km/h


If composite chains and socks offer astonishing performance on snow, at the same level as real Winter tyres, All-season tyres are clearly behind in these difficult conditions. All-season will allow you to respect the ‘Mountain Law’, prevent you from having to switch between summer and winter tyres, and allow you not to get stuck at the sign of the first snowflakes by doing better than summer tyres, but be careful because their adhesion remains very far from what the other authorised devices offer.


For motorhomes that occasionally go to the mountains, a pair of chains, or possibly better socks installed on the drive wheels will suffice in case of bad weather. The former are more effective in really deep snow, but the latter, which are much easier to install (3 minutes per wheel) – are, as the measurements have shown, as effective as snow tyres in terms of traction, braking and grip. All this equipment doesn’t disturb the electronic driving aids (traction control and ESP) but of course, to preserve the lifespan of snow socks & chains, it is absolutely necessary to avoid driving on asphalt, otherwise they will be destroyed very quickly.


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