Chain wear is commonly referred to as ‘chain stretch’, because the chain’s pitch grows in length as it wears. This is the most important type of chain wear, and the growth comes from the bushings wearing with the chain pins. Overtime, the inner diameter of these bushings increase and the pins groove out. It’s often stated that a worn chain is when it reaches one percent growth from the original 0.5in (12.7mm) pitch. Another type of chain is wear is ‘slop’. This isn’t as easy to measure, but this side to side chain wear will lead to slow and inconsistent shifting long before any pin wear is seen.