I put new shoes on the back of my LX last year, and ever since I did, it makes a grinding sound when I stop. I don't know why. I've pulled them apart numerous times to check and recheck them and haven't seen anything that makes sense. I used genuine Honda pads too. They are wearing fine and don't cause any problems other than noise. Just luck I guess.

As far as measuring pad life. That's really hard to judge. It's dependent on how often you stop, and how hard you stop. Usually I just do the rear ones the same time as I do the front ones. This is of course on a car with rear drums. With rear disk, you should have an indicator scraper that makes noise when they need to be replaced.

Tom