Originally Posted by
Sonofamechanic
2 follow ups on this: (1)…wouldn’t the front chainrings be equivalently worn/stretched and also need replacement, or does the shorter radius of the rear cogs somehow cause greater wear or create lower tolerances before skipping? (2) on measuring/checking rear cogs for stretch…couldn’t you cut a short section of tubing/pipe that fits tightly into the ‘trough’ between the ‘teeth’ of a brand new rear cog and then use hat as a measure? When you can wobble it back and forth more than a mm then that cog is worn?
1) Chainrings are generally larger and rotate less, and they're thicker material.
2) KMC makes a sprocket check tool, but the lead mechanic in a shop where I got some training didn't trust it. Others may have a different take on it.