Shimano: In addition to being beautiful, the hollow pattern on the disc can also be used to clean the disc and remove the debris generated during use. Another point is that it can better dissipate heat, reduce weight, and reduce the probability of disc deformation.
Magura: For the hollow on the disc, the two biggest functions are to reduce weight and clean the disc.
Obviously, a disc with a larger hollow area can reduce more weight. On some of the most lightweight XC mountain bikes, there are more hollow discs than those on bikes that have more downhill uses. More hollows reduce weight. However, due to the reduction in the weight of the disc, the heat capacity of the disc is also reduced accordingly.
However, it should be noted that the hollowed-out part cannot be excessively pursued for weight reduction and aesthetics, because too much hollowing will reduce the contact area between the collar and the disc and reduce friction. The friction between the disc and the disc cannot be less than a predetermined threshold. Excessive hollowing will produce a cutting effect, which will reduce the braking performance and accelerate the wear of the collar.
So, what if there is no cutout on the disc? This will make the surface of the incoming film vitrified, especially on some composite materials. The cutouts on the disc will clean these to make the vitrified layer on the disc. On some discs, the edges of the disc are not hollowed out at all. You can observe it if you have the opportunity. You will see varying degrees of vitrification on the film.
Therefore, according to the different scenes of the disc, the hollow style will be different. However, the braking efficiency, heat dissipation performance, and friction will also be different due to the differences between cyclists, so the hollow style needs to be considered separately when purchasing.
TRP: There must be a reason for the hollow pattern on the brake disc. The special hollow design can reduce the impulse and noise in the brake, and it also needs to produce a consistent friction area on the disc. If the contact area between the lead and the disc changes repeatedly, noise and impulse will be generated.
In order to achieve the best performance of the braking system (a closer look at the braking power and adjustment ability), in fact, the braking effect of the disc without hollowing out is the best, because this allows the contact area between the collar and the disc to reach maximum. The same is true in racing bikes. The tires with the best grip are not with various patterns, but with a flat and smooth surface.
However, bicycles are not racing bikes, and the world we live in is not a perfect world, so the discs need to be cooled and cleaned of debris on the brake pads, and sufficient braking power must be maintained. The hollow cut is evenly divided, so that an opening can pass through the disc during the rotation of the disc, which can not only clean the collar but also perform gas exchange to take the excess heat out of the caliper.
Conversely, if too much hollowing is made on the disc in the design, although the heat dissipation performance can be improved and the weight can be reduced, the friction loss between the disc and the disc will be more correspondingly, resulting in overall reduction The braking force. Therefore, the best performance ratio on the standard thickness of the disc is more or less a compromise between braking force and heat dissipation.
However, TRP has the latest 2.3mm thick discs. Here, heat dissipation is no longer the main goal of hollowing out, because thicker discs allow greater heat capacity, so the hollowed-out design goal is to use it at maximum strength. It can reduce the vitrification of the leading piece and maintain the consistency of the braking force.
Hayes: Yes, the hollow style is very important. Hollowing will affect the heat capacity of the disc, the ability to remove water, debris, and sand, the convection conductivity of heat in the caliper, noise, the side rigidity and torsional rigidity of the disc, weight and manufacturing difficulty, and many other issues.
When designing a disc, engineers must balance all these aspects to meet expected performance requirements. For example, during the development of Hayes' D series discs, the shape of the hollow was adjusted, which can significantly reduce noise, and the size of the hollow cut can also effectively control the temperature.