I haven't cleaned them because they were new and looked very clean. Was I supposed to clean them with alcohol or something?
BTW, brakes are only few mnths old. So would few hard stops do the job? And also, is it normal for discs to bend caused by overheating them?
There's a difference between bent and warped. It's not unheard of for rotors to come out of true (warping) due to overheating or rapid heating/cooling cycles, or poor quality, or mishandling. Then there's bent, as when you step on it or bang it down on a boulder or tree stump. Warped rotors you can usually true up using rotor truing sticks or something as simple as an adjustable wrench.
Sometimes, during the manufacturing or packaging process, the rotor will get in contact with impurities that act to reduce friction. On new brakes you'll often smell "burning oil" (Mmmmm... ) as the rotor heats up on longer descents. After a few miles or a handful of hard stops, this will burn off and the brake system will come up to full power.
You can jump ahead by washing your new rotors with dish soap or alcohol. I never do -- just a ride 'er two'll do!
Sanding the pads may help too- after a while, grooves form on both the pads and the rotor which help increase brake strength. Since you don't have any on the rotors, you're losing this part of the equation, and that's what's killing your strength.
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