I got a new bike (Scott Egeniues 920) and after a few rides the rear rotor bent/warped due to long downhill riding (I often go down more than 1400m/4200 feet in one go). When the rotor cooled down, it always got a bit better. But it would worsen with each ride. Eventually, pistons would not go back in completely and the brake would lose its power completely. I repaired everything (the rotor got replaced). A few weeks later, the same thing happened again. ( Shimano BR-MT420 4 Piston brake and the rear rotor is a RT-EM300 CL 203mm with metalic pads.)
Strange thing is that this has never happend with my old bike with cheaper brakes, smaller rotor though I rode the same routes (!) in the same way. The brakes on the old bike were Shimano BR-M506 brakes, SM-RT54 Rotor 180 mm with organic resins.
I searched the web and there are just very few mentions that rotors might wrap permanently due to going downhill/ overheating. My point of view is that this should never happen for a rotor.
What do you think? Any personal experience? Is this a warranty issue? Reasons this did not happen for both brakes?
Furthermore, while it seems more common that overheating brakes can result in temporary loss of braking power, it seems that it should not happen that the brake permanently looses its braking power and requires repair.
What do you think? Any experience? Is this a warranty issue?
Update 1 year after the issue I mounted other (much) cheaper but slightly thicker rotors than the (crappy) Shimano ones. A magnet (for speed measurements) and a bit of tinkering was needed. But ever since the brakes went through many bike park rides and other trips. The issue is gone and I saved a good amount of cash.