How does lubricating your chain help protect your cassette and chainrings from wearing too? I just got my mountain bike back from the shop after a frame warranty, and they replaced my chain as it was apparently worn (2x11). They recommended changing the cassette and chainrings while I was at it, but I wanted to inspect those myself before making those relatively expensive changes.
That got me to think: how does lubricating the chain stop the cassette and chainrings from wearing? You’re not supposed to cover the cassette nor chainrings in lube, so what is preventing them from wearing?
In my case, I noticed that some of my favorite cogs had their contact faces deformed. There was a slight burr where the chain contacts the cog. On the other hand, the big chainring (my favorite) showed significant wear. I’m not surprised by this, considering the occurrence of chainring strikes and shifts under big power, but in some spots I’m pretty sure there’s shavings of metal missing. This corroborates to the fact that I now experience chain slippage every so often when using the new chain. This surely can’t be normal, what am I doing wrong?
I’ve only had the bike for 900km too, and I’m pretty good when it comes to cleaning and lubing. My drivetrain is Shimano SLX M7000 if it matters.
In the ideal case, the chain will not actually be rubbing significantly against the chainrings under load. As the chain wears, the spacing between the chain links becomes different from the tooth spacing, and this difference in spacing means that there is sliding contact as the teeth engage the chain.
The rollers inside the chain help to convert some of this sliding motion into rolling friction (transferring the actual sliding contact to the more protected and better lubricated internal joints of the chain), but any binding of these rollers against the pins again leads to sliding contact between the tooth and the chain.
Keeping the chain lubricated (and, as noted in the question comments, clean) will both minimize the wear that stretches the chain and prevent roller binding, thus reducing the wear on the teeth.