and thats why there are tolerances for rotor thickness on each vehicle that are observed...and if ur sayin only resurface when necessary as in doing pad swaps and not touching rotors if they "look fine" then thats the worst thing you can do...because ur pads will not sit correctly against your rotors causing the same problem as before as well as abnormal and increased pad wear...the general rule of thumb is two resurfaces per rotor as long as its normal wear then its time to junk them and put new ones on it