Originally Posted by
Raxel
And I've heard that smaller cogs (9,10T) wear out pretty quickly if you use them often.
This because there are fewer teeth to spread the load exerted by the chain, so each tooth sees a bigger force so they wear quicker.
A slightly different argument must be applied to smaller front sprocket: Chain tension increases with smaller sprockets, causing rapid wear to the dual effects of fewer teeth to transfer the load, and higher tension causing even bigger tooth force.