Today I checked the front pads thinking it was getting close to replacing them. I have a new set ready to go but to me it looks like I still have 50% of the pads remaining. What I'm concerned about is that with this much pad remaining it looks like the sensor is just about to touch the rotor. Is that about right? I guess by the time it wears down the sensor to trigger an alert the pads might be at 20-30%??