Originally Posted by
Psimet2001
That's contamination. Unless I missed something you haven't been changing your rotors. New rotors and pads at the same time so you don't contaminate them.
Now you need to make sure you aren't cleaning the bike with anything that is getting on the rotors. Also chain lube. You'd be surprised how chain lube can get everywhere at speed.
Contamination is an issue, but not in my case, I always take care. Months ago, I re-surfaced the rotors as new and deeply cleaned them with alcohol and car disk cleaner. After bed in with new pads they worked perfectly, but again… only for +/- 200 km.
As a side note, the rotors got deep circular scratches very soon after using them as new (and after re-surfacing). This comes from the metallic insertions in the pads. I did not see such scratching effect with two other bikes (rented mtbs, Tektro brakes, during hard braking on descents).
I know it sounds weird, but I think the system is wrongly designed for casual riders who ride on flat roads and do not need to brake long and hard, as professionals do. The pads simply get clogged fast with their own generated fine powder that acts as a graphite powder lube. The pads auto clean during long and hard braking and then work ok for a while, but without that they remain clogged and get poor performance.