[kolosy]

Originally Posted by M3SQRD

The pad radial depth (PRD) doesn’t match the rotor radial depth (rotor annulus depth = rotor OD - rotor IR) and/or the PRD radial positioning may be offset from the rotor annulus depth which can result in pad overhang on the rotor IR or rotor OR (PRD = rotor annulus depth but the caliper bracket incorrectly aligns/centers the pad on the rotor) and/or the pad material may have been incorrectly placed on the pad backing plate (or in your case you’ve switched pads from different manufacturers).

All of the above can create unswept or overhang rings on the rotor IR or OR. It’s hard to tell from this picture but it looks like the first pad used the full rotor surface and the second pad PRD is shorter than the rotor annulus depth. It would be easy to identify the car if you had it sitting in your garage.

Here’s a picture showing the pad PRD was too short:

Ok, but why would that create a groove, instead of just a step down?