Originally Posted by
Jipe
I do not have this setup long enough (only since September 2019) to give a feedback about longevity of the 9t cog.
But with the wheel size and the chainring size I have, I do not use very often the 52-9 combination, only when riding quite fast.
Since the 10 smallest cogs are in steel do not think that wear of the 9t will be a problem.
The efficiency drops with cog size, particularly quickly at the small size end, if anyone cares, as the pull force from a chain link is more and more misaligned with the usable pull force for the next link. This ties to the wear as more and more work is done by the leading tooth that wears at an accelerated rate.