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  Hydraulic Brake - Brake Disks 2

If the brake disk has been invented by the Lanchester Motor Company in 1902, but only entered mass production around 1955, the first patented internal ventilation system from 1929 is remarkable. Another interesting fact is that it not only transported air from the inside to the outside, but the disk was directional already.

We have already noticed that, except in very rare cases, brake disks are only attached to the outside of the wheel hubs. They last their lifetime within more or less large rim bowls. In contrast to drums, the area towards the brake pads is smaller. In order to achieve the same braking effect, the contact pressure forces must be significantly higher.

Basically, the brake pads of disk brakes wear out more quickly and would depend on ventilation through the rims to dissipate the larger amounts of heat. However, as these can be very different in design, the only reliable cooling is the internal and/or external ventilation. In very rare cases, special cooling channels are led to the brakes.

These and ventilated brake disks are usually found at the front, because that is where the greater braking force has to be generated. Unfortunately, internal ventilation increases the already high unsprung masses due to the material grey cast iron. Ceramic disks for passenger cars can weigh less than half that.

Although there are also internally ventilated ceramic disks (picture above), we stick to those made of metal and, looking from the outside, distinguish between smooth, drilled and grooved disks. The internal ventilation practically divides the brake disk into two parts, which can be connected by the same material. These can now be strictly radial and straight from inside to outside or have a certain curvature.

The latter are also referred to as 'directional'. Therefore, different disks are required on the left and right. In addition, the channels are not of much use if the disks do not have corresponding openings on the inside (picture above). The disk in the picture below shows you better the special guidance of the channels of a directional disk.

The drilled holes across the disk originally had the purpose of discharging gases formed towards the brake pad and disturbed the braking process. This was mainly the case with asbestos as a carrier material was still permitted in those days. But under very high stress far outside normal use, deflagration can still occur on brake pads today.

Please note not only the continuous grooves at the bottom of the disk, but also that the connectors are different sizes inside and outside. They are also called knobs. So there are no longer individual channels, but the air can also freely find a way out between the individual connections in other constructions.

In this case the brake disk is not directional and there is more contact between the two large plates of the brake disk and the air flowing through. In addition, the design with the knobs is intended to counteract cracking, because this is only possible between two of them.


Even if the holes at the top are chamfered all the way up in the disks and the edges of the grooves are also carefully machined, it is very likely that there will be noticed higher wear on the lining. This could also be the reason for a higher noise level. And although the effort is relatively small, as you can see in the last video below, the disks might be more expensive.

With all this, the optical effect of such disks should not be underestimated. The two last shown here cannot keep up with this. They are intended to illustrate once again the difference between channels (above) and nobes (below).

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