Wear: When do brake discs and pads need changing?

19. Jun 2019 | Brake | Technology + Products

The brakes of a passenger car not only have to withstand extremely intense usage. The brake system and all its parts are also an important safety factor. And so perfectly functioning brakes are absolutely essential. Which is why they should be checked every time a car is taken for servicing. But when do brake discs and pads need changing? And how is it possible to tell when they are worn?

How long is the service life of brakes?

It is unfortunately not possible to make any generally valid statements about the service life of brake discs and pads. A number of factors govern how long brakes function properly: The working life is influenced in particular by driving style, vehicle weight and materials. Wear and tear on the brakes also depends on whether a vehicle is driven a lot on motorways or more in urban traffic. One thing is clear: Brake discs and brake pads are subject to wear over the course of time, as they convert kinetic energy into thermal energy through friction.

It is quite possible for careful motorists to get 100,000 kilometres or more out of one set of brake pads. Drivers who prefer a speedier style have to change brake pads far sooner. Intervals of 10,000 to 15,000 kilometres are not unusual. The same rule also applies to brake discs: The more intensively they are used - as a result of frequent, sharp braking for example - the sooner they have to be replaced.

When should brake pads be changed?

At the latest, brake pads should be replaced when they are worn down to a thickness of less than two millimetres. Most modern cars are fitted with wear indicators to warn drivers when replacement is due. With electronic systems, wear is accordingly indicated by a warning light in the dashboard. With the purely mechanical version, a metal pin inserted in the pad makes an unpleasant noise on reaching the wear limit as a result of the metal pin coming into contact with the metal of the brake disc.

When should brake discs be changed?

The crucial aspect with brake discs is the so-called "minimum thickness". This is the minimum dimension that every brake disc must have and which is specified by the manufacturer. It is abbreviated to "MIN TH" and can be found on the rim or at the chamber of the brake disc. Two to three millimetres of wear are generally acceptable.

Natural brake disc wear is relatively easy to detect. When a disc is worn, a burr can be felt at the rim, as the disc only becomes worn where the brake pad is applied. The more pronounced the burr, the worse the disc wear is. Experts use special instruments to measure the thickness of the brake discs.