First, the Installation of Disc Brakes:
To this day, we believe there are still many cyclists who don’t know that “the disc brake caliper can be adjusted left and right on the adapter.” It was only after receiving feedback from many “hands-on” cyclists that we learned:
Many cyclists rely on methods such as “adding shims” or “filing down the disc brake mount on the frame” to achieve “caliper left-right position adjustment.”
Of course, this is not the correct way. Below, we’ll use this image to explain the proper method for adjusting the left-right position of disc brakes.
First, fully secure the adapter to the fork or frame, integrating the adapter and the frame or fork into one unit. Then install the caliper onto the adapter. After fixing and adjusting the overall left-right position of the caliper, secure the two screws on the caliper.
To achieve this installation effect, you’ll need some small techniques. You can refer to the video below.
Second, the Braking Force of New Discs:
New discs cannot achieve “full lock,” which should be common knowledge among experienced cyclists, but many beginners are still unaware. Beginners often ask, “I can lock the brakes on other people’s bikes, why can’t I lock the brakes on the ones I bought from you?”
Here’s the explanation: The surface friction coefficient between a brand-new disc and the brake pad is not high enough. This is because the surface of a new disc is relatively rough—using a non-strictly technical term, the “surface particles are larger,” resulting in a “smaller actual contact area between the disc and the brake pad.” Therefore, insufficient friction force is generated during braking, which is why “full lock” cannot be achieved. This issue can be resolved after a certain amount of braking, as the friction will “polish” the disc surface smoother through the pads. Once the surface particle size is reduced, the “effective contact area” increases, and braking force improves. (This is just a general description—physics experts, please don’t nitpick the details.) When you see obvious polishing marks on the area where the disc and brake pad rub against each other, it basically means the disc has been “broken in,” or in other words, “the disc has been worn in.”
Only after the disc is “broken in” does the contact surface between the disc and the brake pad reach maximum friction coefficient, allowing for full lock. So, to all cyclists who have just installed disc brakes and find they “can’t lock,” don’t worry—it just needs some bedding-in.
Third, Resonance Noise During Braking
Quite a few cyclists ask, “Why is there such a loud strange noise when I brake? How can I eliminate this sound?”
First, let’s answer the latter question: “This sound is resonance, and it cannot be eliminated. It occurs in all disc brake use above a certain braking force level. It may increase or decrease in volume depending on other conditions, but it can absolutely not be completely eliminated.”
Then, let’s briefly discuss the origin of this “sound”:
Starting from the basics, the most fundamental action of disc brakes is “the friction between the brake pad and the disc.” We believe all cyclists can understand that. But everyone seems to forget some of the most basic physics knowledge learned in school—that “non-mirror-surface friction (the disc and pad are definitely not mirror-smooth) will inevitably produce vibration, and vibration will inevitably produce sound.” This is an unchanging principle of physics and will not change based on cyclists’ wishes to “eliminate the sound.” Therefore, this sound cannot be eliminated.
Next, let’s talk about under what conditions this sound becomes louder or quieter.
As mentioned earlier, “sound is generated by vibration,” so the volume of the sound naturally also depends on the magnitude of the vibration. The greater the vibration generated during braking, the louder the sound. So what affects the magnitude of this vibration?
1. Relative Displacement: Actually, this “sound” that bothers many cyclists only occurs within a very small range. To put it in more common terms, it only occurs at the “brake lock threshold.” Once locked, there is no relative displacement between the disc and the pad, and thus no sound is produced. So actually, cyclists don’t need to worry too much about this sound. First, because of the friction coefficient, new discs cannot “normally lock,” so even if you squeeze hard, there will still be relative displacement, which will inevitably produce some sound.
Then, even after the disc has been “broken in,” the sound will only occur when your control is extremely precise—at the point where the disc and pad are just about to lock but haven’t quite yet.
2. Friction Coefficient: If the disc accidentally gets oily, the most direct impact is that it “cannot lock.” In this case, no matter how hard you squeeze, the disc and pad will still slide against each other. It can be roughly understood as generating sliding friction between the disc and pad under a relatively high pressure, which intensifies the vibration-generated sound.
3. Braking Force: Another key factor related to the magnitude of vibration is “braking force.” The greater the braking force, the greater the “relative pressure” between the pad and the disc. Under such conditions, if there is also relative displacement, greater friction force is naturally generated, and the vibration becomes more noticeable. Therefore, it can be said that the “resonance” sound is more pronounced in hydraulic disc brakes, while some low-end domestic disc brakes hardly produce it at all.
4. Frame Structure: During the process of vibration generating sound, there is a phenomenon called “resonance.” The frictional vibration between the pad and the disc can drive the caliper, adapter, and even further resonate with the rear fork disc brake mount part of the frame, thereby amplifying the sound.
For example, the resonance sound from the rear fork of a Merida frame is relatively weak because Merida frames have very thick tube walls, ample material, and a nearly solid structure that reduces the resonance between the rear fork and the caliper. However, many frames with large cutout structures, such as the French Commencal frames, feature a uniquely “fully open disc brake mount” that reduces weight while forming a relatively slender triangular frame structure. This structure is more easily driven into similar frequency vibrations when the caliper vibrates, making the sound more noticeable.
This post has been synced to Bicycle — Ado’s Weibo