Chain wear gauge for measuring chain length

A derailleur chain can still be fully functional, but after a certain degree of wear it no longer fits exactly into the sprockets. During use, the chain elongates due to stress and gouges the chainrings and the sprocket, i.e. the “grooves” of the sprockets are widened. If a new chain is then fitted, it no longer fits the grooved sprockets/sprockets and jumps over the teeth under load.

It is therefore important to change the chain early if the elongation of the chain exceeds 0.75% (for light alloy cassettes) or 1% (for steel cassettes). First insert the narrow side into the chain links and then the .75 side. If the gauge rests parallel on the rollers over the entire measuring length, the chain is worn.