How long do disc brake pads last?

Rim brakes also suffer from the disadvantage of rim heating, because the brake converts kinetic energy into heat, which increases the temperature of the rim (the brake caliper and frame do not become hot because brake pads are excellent thermal insulators). In normal use and with lightweight bicycles this does not present a problem as the brakes are only applied with a limited force and for a short time, with the heat being quickly disspated to the surrounding air. However, on heavily-laden touring bikes and tandems in mountainous regions the heat build-up can be sufficient to increase tire pressure to the extent that the tire blows off the rim. If this happens on the front wheel a serious accident is almost inevitable. The problem is worse when descending cautiously at slow speeds because the brakes are "always on" and the cooling airflow over the rim is insufficient. The risk can be minimised by not over-inflating tires and the adoption of an aggressive riding style, only braking for the corners, but the real solution is a hub brake or a disc brake which allows the rim to remain cool.