A lot depends on just how “bad” the rotors are…If they are really ripped up, badly scored, the new pads will QUICKLY wear out and your braking ability greatly reduced because of the over-heating and poor pad contact. Sometimes you can get away with minor scoring, but the pads will still wear quickly and it takes a while for the pads to “wear in” (to the uneven surface) and until that happens, braking is poor…Noise and rumble and squealing is to be expected…