When it exceeds the stretch limit indicated by Park Tool CC-3. I check at least 4 different sections of chain, since they can stretch unevenly. Chain life varies widely depending on usage and quality. I've gotten over 5000 miles on road chains on geared bikes and only 500 miles on my cross bike.
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What, Me Worry? - Alfred E. Neuman
I'd like to think i have as much money as brains.
I see the light at the end of the tunnel, but the tunnel keeps getting longer - me