I have been maintaining two bikes for a few years. Both have disk brakes. One has around 10 000 km on it another one is well over 35 000 km. The disks on the bike with 35k+ are now reaching their end of life. They are cheap Tektro disks from early 2000s. I will be replacing them soon.
However I also maintain a relatively new bike that I have built up myself. This one has:
- Shimano XT flat mount callipers (front and rear)
- Shimano RT-86 rotors front and rear.
- Shimano resin pads (K03S initially and then switched over to L05A)
To my surprise the rear rotor has worn from new downto 1.3mm in under 6000km. The front one is now at 1.5mm (which is Shimano recommended scrap limit). There has been no brake rub, I used original Shimano resin pads only. Never used these rotors on any other bike or with metallic pads. Change of pads I made at around 3000 km was not due to pad wear but due to contamination. Overall I would estimate I have worn through about 1 full pair of pads in that time.
The calliper I used to take measurements is in a good state and I would rule out the measurement error. Also the lip on the edge of the 6000km rotor is noticeable and even more pronounced than the one on 35000km Tektro rotor...
There has been no substantial difference in riding conditions between old and new bike. If anything I would argue that new bike brakes had an easier life...
That situation made me think. Rotors on one bike have worn out much faster then the other and much faster then I expected them to. I tend to go on bikepacking trips in mountainous regions where I go multiple days (weeks?) unsupported with a loaded bike. It is very realistic that a rotor could fail under these circumstances.
What are the failure modes of the brake rotors if you push them beyond limit (not that I intend to). I tried googling but did not find anything substantial.
What are the critical signs to look out for on a trip (assuming you don't have a vernier calliper and don't even have a habit of checking your rotors regularly)? One thing that I noticed is that the sound changed when breaking. Instead of a continuous hissing noise that disc brakes normally produce, I get the hissing noise + pinging noise as if someone is touching the spokes. I am almost sure the spokes have nothing to do with this.
Is it normal for brake rotors to wear out as quickly as pads??