They have strange notions about motor cars in Germany. I have stood, for example, by an empty country road and shivered in the rain with several law-abiding citizens while we waited for the little man in red to change to green before we crossed - with not a motor car in sight.
Likewise, when you park your car in the place allotted to you near your house, it must be exactly senkrecht to the footpath, or you will cause intolerable angst. If the angle is ever so slightly more than right, or slightly less, you will be told politely but very firmly, as I and many of my friends have been, that deviations from the perpendicular are simply "nicht erlaubt!".
And in the third week of November the motor car takes precedence even over Beaujolais Nouveau and the start of Christmas shopping. This is when you must have your wagen fitted with its winter tyres. But, not to be too beastly to the Germans, it must be said that on the Continent, the concept of winter tyres makes sense.
Rain or snow diminish a tyre's grip. In the case of rain, since water cannot be compressed there is a continuing tendency for a tyre on a wet road to rise and skim across the surface of the liquid. This tendency to aquaplane is enhanced with increasing speed; the higher the speed, the less time the water has to get out of the way. It is diminished if the tyre is provided, as most tyres are, with little grooves which allow the water to escape to the side of the tyre, thereby allowing the threads to stay in contact with the road.
But snow requirements are quite different. Deeper and much chunkier threads are needed, and much wider grooves. The tyres need to be able to compress the snow in their grooves and then release it again as they roll along; if the grooves are too small, the "bites" of snow they take on each revolution are so small that traction is significantly reduced.
The other major difference between winter tyres and summer tyres is in their composition. The rubber of summer tyres hardens and becomes stiff and unpliable at very low temperatures, and thereby loses its gripping power. Winter tyres, on the other hand, are softer, which helps to maintain their grip even in freezing conditions. But the soft rubber of winter tyres wears quickly on hot summer roads, and the chunky threads are rather noisy. So come spring, you have to change your tyres again, which shows that a motorist's work in Germany is never done.