Evaluation Of Surface Roughness Information

Information 

• An increase in surface roughness impairs braking comfort (rubbing, shaking in steering wheel, scraping noises) and increases brake pad wear.
• A roughness value > 80 μm (micrometers) means that the parts must be replaced as a precautionary measure.

Information 

Examples of different types of wear are shown below. The brake disc must be assessed according to these and then replaced if necessary.

Two illustrations of the same peak-to valley surface roughness (views 1 and 2) help to make a better assessment.

1. New brake disc. (Surface roughness < 80 μm)

   The early stages of roughness are indicated by burnt-out carbon fibres on the surface of an otherwise intact, semi-matt surface. The surface feels smooth.

   No replacement necessary. 

   1. 1.1  Surface roughness = 6 μm (view 1) > PCCB surface roughness (Sr) = 6 micrometers (view 1) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 6 micrometers (view 1)

   2. 1.2  Surface roughness = 6 μm (view 2) > PCCB surface roughness (Sr) = 6 micrometers (view 2) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 6 micrometers (view 2)

2. Brake disc is not yet worn. (Surface roughness < 80 μm)

   In the advanced stages of fibre burnout and the initial destruction of the Si and SiC "matrix", the depressions have become more pronounced. Large sections of the surface are still intact, the depressions form an even, fine-grained pattern.

   The surface still feels matt, however, and the roughness is not yet pronounced.

   Borderline disc, which can still just be evaluated as OK. As a result of more advanced damage to the surface, the depressions are larger, and above all deeper, compared with the previous surface condition.

   On the one hand, the more extensive roughness is noticeable (only when a comparison is made); on the other hand, however, like before, "only" depressions are observed.

   Replacement not yet necessary. 

   1. 2.1  Surface roughness = 72 μm (view 1) > PCCB surface roughness (Sr) = 72 micrometers (view 1) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 72 micrometers (view 1)

   2. 2.2  Surface roughness = 72 μm (view 2) > PCCB surface roughness (Sr) = 72 micrometers (view 2) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 72 micrometers (view 2)

3. Brake disc is worn. (Surface roughness > 80 μm)

   Worn surface. Advanced wear has led to a situation where only the remains of the original surface are left.

   It is clear that the roughness is caused not only by depressions but also by bumps.

   Replace brake discs. 

   > 465119 REMOVING AND INSTALLING FRONT PCCB BRAKE DISC 

   1. 3.1  Surface roughness = 108 μm (view 1) > PCCB surface roughness (Sr) = 108 micrometers (view 1) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 108 micrometers (view 1)

   2. 3.2  Surface roughness = 108 μm (view 2) > PCCB surface roughness (Sr) = 708 micrometers (view 2) 

      Courtesy of PORSCHE CARS NORTH AMERICA, INC.

      PCCB surface roughness (Sr) = 108 micrometers (view 2)