Well, in theory, since tooth wear is primarily caused by running a stretched chain (hence loading the teeth individually rather than spreading the load between many teeth) then running a succession of unstretched chains should give maximum cassette life. Of course, the teeth will still wear down (albeit at a reduced rate) and at some point, wouldn’t continue to mesh with new chains, which is why you have to go back to the first (already partially stretched) chain at some point and start the process over. From what I’ve read, 3 to 4 chains in rotation for 500 miles each is the sweet spot for this. One guy on MTBR was even flipping each chain over half way through its cycle.
I hasten to add that I’ve not tried this for myself, it’s just what I’ve read – this practice wouldn’t make sense with my current cassette (XT 11-36, £34 at CRC) but I might try it when it’s time for a new drivetrain (will probably change to XX10s or XTR11s cassette then)
