I have about 8600 mi on my FZ6 and the brakes are fine, but just wondering how to tell when they need to be replaced. I have heard that aftermarket pads make a big difference.
If you look from the front of the bike into the open end of the caliper you can usually see the pads. The part of the pad that is between the disc rotor and the metal backing plate of the pad assembly is the friction material. Many pad do have a groove cut in the middle of the pad that shows you the wear limit. Many do not have the groove. You look at both the right and left pads and judge how much is left. If there is less than 1/8 of any pad left, it is close to time to replace the pads. Stock pads from your bike's manufacturer work well. I always replace pads with EBC brand HH pads and have always had good luck with them.
Most calipers allow you to look down on the top of the pads, if you can see a groove cut vertically down the pad your pads still have life in them (provided they are not contaminated or glazed). Sometimes aftermarket pads make a difference but there is no point in getting sintered race pads if you do not ride at those speeds, so choose with care and research.
I was going to answer this, but honestly I couldn't put it better than Tim D. His answer is spot on.
