We've all done it; intended to change a chain a bit sooner than we actually did, and fitted a new one only to find that it skips on the worn sprockets. Occasionally I have 'fought the system' and run a new chain on slightly worn sprockets until everything beds in again. But it can take a while and there is always a risk of skipping under some load.
I've tried de-hooking sprockets (by grinding) and this is only a partial success; the problem being that once the sprocket is slightly hooked, the roller wants to sit in the hook, which is at a slightly larger PCD than with an unworn sprocket. As each tooth comes under load, the roller rides up a little ramp into the hook, and this affects how the other rollers sit in the sprocket too, such that even if the hook is removed, the chain may not feed cleanly onto the sprocket as it leaves the rear mech.
shows the wear ramps very clearly, although this is an extreme example. To make a worn sprocket work OK with a new chain, I think it is necessary to remove the hook and the ramp.
My plan (such as it is) is to have several chains at my disposal, lets say 0.4%, 0.2% worn as well as new chains to hand.
Lets say I run a chain out to 0.7% and a new chain skips on the cassette. I would then run the 0.4% chain (which ought not skip) for a while ( a few hundred miles). Then I'd run the 0.2% chain for a while, and finally the new chain ought to run OK perhaps.... The idea is that at each stage the chain isn't liable to skip, but the worn sprockets are gradually recovering their shape such that they will tolerate a new(er) chain.
Has anyone tried this sort of approach...?
cheers
