The general reasons are as follows: dirt such as water or mud sticks to the optical disc or the incoming film, and the surface of the optical disc will be uneven and impurity. There will be irregular vibration and screaming when the disc brakes, but it generally has little effect on performance and can be ignored.

Solution: You can remove the disc brake, clean the disc and incoming disc with brake cleaner, and pay attention to protect the mother disc from being scratched by the disc. Then polish the disc with sandpaper, and polish it clockwise, and polish it evenly according to the texture of the disc (generally, it is enough according to the degree of wear marks 10 circle, and it is similar according to the flatness of the disc surface). By the way, just polish the film a little and smooth it, you don't need to grind it too much! Just dry it, and finally put it back!

Extended data:

Reference factors for choosing mountain bikes:

1. Riding intensity

According to the classification of mountain bikes, they can be divided into two categories: leisure sports and competitions. The route of the former is mainly asphalt road and low-difficulty silt road, while enjoying the beautiful scenery along the way to achieve the purpose of exercise and fitness. The latter route emphasizes taste, and the riding intensity and height have a certain level.

2. Dimensions and accessories

No matter what kind of riding type you choose, you must choose the right frame size and fit it to adjust the appropriate riding posture, otherwise even if you choose top-class car models and spare parts, it will not meet your riding needs and even affect your sports efficiency.

It is especially recommended that the distance from the crotch to the upper tube should be higher than two fingers, which is an ideal state.

Test ride

Although riders first consider exterior painting, just like buying clothes, they usually have to try it on to know what it feels like. The same is true for bicycles, because buying a car is not just about appearance, but more importantly, riding.

References:

Mountain bike-Baidu encyclopedia