Wipe the chain with a rag after riding in rain or mud. Every few hundred kilometres, scrub it with a brush and degreaser, rinse it and let it dry. Put one drop of chain lubricant on each roller while turning the pedals backwards, then wipe off the excess. Too much oil collects grit and wears the cassette and derailleur. A chain stretches with use. A cheap chain checker shows when it has reached 0.5 percent wear; replacing it then saves the sprockets and chainrings.
