To alleviate poor shifting and uneven drive train wear, manufacturers recommend chain replacement before rear cog replacement. Now you can quickly and accurately determine the wear and stretch of any chain with the Park Tool Chain Checker. Simply insert tCompatible with all bicycle chainsFor modern 9 and 10 speed chains, replace chain at or just before the 0.75% readingsFor 11 speed chains, replace at or just before the 0.5% reading
