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While riding my single speed Salsa El Mariachi at River Bends this evening I dropped my chain. Since the dropouts hadn’t moved, this led me to thinking the chain had stretched. After getting home I measured it, and at 1/16″ of stretch over 12 links (12″) it met the fairly universal (and Sheldon Brown-blessed) definition of time-to-replace.
Shown above is a brand new SRAM PC-1 single speed / BMX chain hanging next to the worn chain. The tops of the chains were aligned and clamped in place, showing that just with gravity loading the chains there is almost 1/4 of a link of stretch over the length of the chain. This amount of stretch is enough to begin unevenly wearing teeth on the chainring and cog, which dramatically accelerates wear on these more costly parts. Thus, the chain shall be replaced.
ADDENDUM: I have been reminded that chain stretch isn’t actually stretching. So, for sake of clarity: stretch is actually elongation of the chain due to wearing of the plates and pins. During use the rollers and bushing also wear, but these don’t contribute to overall chain elongation. Roller and bushing wear will make chain measurement tools such as the Park Tool Chain Checker (CC-2) and Chain Wear Indicator (CC-3.2) provide false positive results, leading to premature chain replacement. This is covered in depth over here at pardo.net…