As a rule of thumb, one should replace the chain every 1000 to 5000 km, depending on the force you exert when cycling. Since the chain otherwise tends to stretc

As a rule of thumb, one should replace the chain every 1000 to 5000 km, depending on the force you exert when cycling. Since the chain otherwise tends to stretch, it will eventually be misaligned with the chain wheels and start to wear those down. As the latter are more expensive to replace, it’s a good idea to replace the chain first.