How long disc brake pads last depends on how much you ride, how heavy you are, whether you predominantly brake by grinding or rather at intervals, whether you also ride in dirty weather and whether your brakes are serviced regularly.
At some point, however, all the pads are worn out: At the very end, you can hear the sound of metal on metal when braking. This is the latest point at which the pads need to be removed before they ruin the discs. It is better to keep an eye on increasing wear: If the pad thickness is less than 0.5 millimetres, they should be replaced. Take your pads out to measure them, as they are often worn unevenly.
But the discs also wear out. Measure their thickness at least once a year with a caliper gauge. Their minimum thickness also depends on the make and is sometimes indicated on the disc. Important: Always refer to the operating instructions to find out exactly how the wear limits are defined.
