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All Tests

  Brake Disks 3

The picture itself is very interesting. It shows a driven front tool of the Cayenne Turbo with air suspension and split upper wishbone. But what we want to focus on in this chapter is the brake, not so much the ten-piston fixed caliper, but the brake disk, which is supposed to be coated with a new kind of process.

This Porsche Surface Coated Brake is standard in the Cayenne Turbo with white brake calipers. Otherwise, it costs about 3,000 Euros extra, about a third of that for a ceramic brake. A world first, as Porsche says, can at best be the method of applying the tungsten carbide to the surface of the brake disk.

Coatings of brake disks with ceramic material are not new, corresponding patents are more than 10 years old. Also such are even offered on the Internet, but certainly not comparable. Please note, it is the same surface that the brake pads access. The layer is be only 0.1 mm thick, underneath the 'normal' grey cast iron disk. In general, you can assume a Porsche or Bosch-own special alloy here.

You will notice that no matter how hard the material is, we have a little trouble describing how it works. After all, the brake disk surface should only develop its special shine after 600 km. It probably also depends on how these 600 km are managed. Because the whole construction is supposed to show its advantage on the race track, where it should provide a very special deceleration with considerably reduced heat development.

By the way, the color of the white brake caliper is not choosen at random. It is because this brake produces particularly little brake dust. According to Porsche, the need for servicing is reduced by 30 percent. If it were not so expensive, it could solve a problem of electric cars, rusting or corroding brake disks due to infrequent operation. According to Porsche this cannot happen to you with this brake.

The neutral rapporteurs agree on the material, but not on the method by which it is applied. As the name suggests, tungsten carbide is made up of tungsten and carbon. The process of hardening is often referred to as 'carburising', here again assisted by an even harder material. This is probably only possible by flame spraying at high pressure and temperatures, because the melting point of tungsten is just under 2,900°C.

The surface should therefore be ten times as hard as that of grey cast iron disks. And now it gets a bit confusing, because Porsche naturally wants to prove that this brake contributes considerably less to the fine dust problem than 'normal' brakes. In this context it is astonishing to note that the brake disk accounts for 70 percent of the brake dust and the pads for only 30 percent. Somehow the experience of decades is turning this upside down.

With regard to the pure ceramic brake, we once learned that the pads had to be replaced every 80,000 km and the brake disk only after 300,000 km. Of course, this first of all fits in with the manufacturer's statements. But how does this fit with a layer on the brake disc that is only 0.1 millimetres thick? You would have to measure a ceramic disk that has been replaced after 300,000 km and then you could calculate the wear back.

English subtitles possible . . .

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