Microcracks in Brake Discs: Why Do They Appear?

We constantly analyze every element involved in the braking process of a motorcycle, and most of the time, the components that attract our attention are the brake pads and the discs. In this article, we focus specifically on the microcracks that can sometimes appear on a brake disc.

Before getting into the subject, we want to emphasize something important: the braking system of a motorcycle does not consist only of the disc, the pads, the brake line, and the lever. There is another key element that is often overlooked, and that is the tire.

The tire’s grip limit is a determining factor when it comes to helping the motorcycle stop effectively during every braking action.

Now, regarding microcracks: these are tiny fissures that appear on the surface of the brake disc as a result of repeated cold-to-heat and heat-to-cold cycles.

These small cracks can sometimes be an early sign of the feared “cracking” phenomenon, which means we should monitor them carefully. We certainly don’t want them to grow larger and eventually become a dangerous fracture that compromises the disc’s condition.

In most cases, these microfissures do not reduce braking performance. In fact, in competition environments they are fairly common due to the extreme stress discs are subjected to.

For everyday road riders, especially those using the bike moderately, it is possible to feel a slight “jump” or irregular sensation through the brake lever. This subtle vibration depends greatly on each rider’s sensitivity.

Visually, these “vein-like” marks may seem worse than they really are, because the black dust produced by the brake pads fills the grooves and highlights the cracking effect. In reality, their depth is usually minimal.

Discs with a slotted design tend to suffer less—or almost not at all—from this phenomenon. On the other hand, drilled or perforated discs have a higher likelihood of developing small fissures around the holes.

Ironically, the very purpose of those perforations—to improve cooling—also makes the area more prone to thermal stress and the formation of fine cracks.

Paying attention to these details and maintaining our motorcycle properly is an essential part of the safety measures we should always prioritize.