Over time, the rubber of brake pads hardens, and thus becomes less effective at braking. The hardening takes place especially on the exterior of the rubber (sort of like cheese) and is specifically problematic on the part of the pad that contacts the rim; braking effectiveness is compromised.
I've found it useful to buff the pads with sandpaper to remove the thin hardened layer, and have noticed significantly increased braking performance on some old bikes whose pads I've scrubbed.
The downside: I think it's possible that grains of sand can get stuck in the rubber, and pressed into the pads, to kindly grind down your rims later. I've noticed this in a set of pads that I sandpapered yesterday. Two explanations:
- I'm using the same piece of sandpaper that I have for quite some time, and the sand on it has become loose from so many uses, and thus pieces of sand dislodge and get caught in the pads, pressed into the rubber.
- There was already grit in the pads from being used for a long time, and the sanding just removed some of the rubber around the grit, making its presence in the pads more obvious.
So, perhaps there'd be no problem if I were careful to use newer sandpaper when I do this. Or maybe there's no problem at all, and it's just old grit. (I've been picking up the grit, whatever it is, with the point of a razor blade.)
What do y'all think?