Originally Posted by
FBinNY
... As a chain wears it's pitch increases and as sprockets wear their effective pitch decreases. ...
yes re chain, but no re sprockets. the pitch stays constant as long as the teeth are evenly worn. what kills a sprocket is when the teeth get scalloped and rounded off. a stretched chain puts ALL the force on one tooth, since the next link is loose on the next tooth, this greatly accelerates the wear on said sprocket teeth, and eventually leads to the chain links skipping on the rounded off sprocket teeth.
using the largest chain-ring practical for the gear range you are in greatly helps this. the larger chain ring sends less force down the chain, and distributes the wear over more teeth. larger chain ring also implies larger rear cog (at the same effective gear ratio), so this applies doubly so.