Sometimes it's a bit of sand or sharp grit but many times it's bits of aluminum that seem to melt into the pads... After removal the tiny crater attract the minerals the wear into the rims. Happens to me most of the time during the rainy season.

In my supernumerary condition, (Methuselah), I don't ride in the rain any more unless I get caught in a sudden deluge or sprinkle but it's more the wet grit that gets picked up when riding after it rains.

As far as "dressing" the face of brakes pads, I found that 3M Medium Drywall Sanding Screen works well. I use it even on new brake pads to remove ~.5mm of the surface to get below the hardened zone that results from vulcanizing or some other final processing step. The abrasive coated screen keeps the dust from building up like what happens with sand paper.



I also have a 6" or 8" Flat Bātard (Bastard) File for more aggressive material removal.

verktyg