A used chain considerably increases imprecise gear changing, more noise and causing more damage to the overall drive-train. This because the stretched chain hinders the correct tracking between the mechanical parts, increasing the working tolerance thus causing more damage. Within minutes you can replace a worn chain and bring the performance of the changing rate back to a 100%, with only a few simple tools and knowing your groupset speed - in the case of mounting a Shimano chain, remember to mount it in the right direction. The bike will be much happier with the transmission in perfect state and our expectations will be met thanks to a sweet and smooth shifting under all conditions.