The chain transfers power from the chainring to the rear hub's sprocket. It is subjected to extreme loads as well as weather conditions. Chains stretch at different rates depending on the usage conditions, but each one must be replaced sooner or later. Timely replacement of the chain is the only way to protect chainrings and sprockets from excessive wear. To maintain the optimal performance of the Shimano HyperDrive System, it is important to use original Shimano HG chains.