Sprocket wear hides in plain sight: the teeth reshape so gradually that owners stop seeing it, until a mechanic points at shark fins where hills used to be. Here's how to read the teeth — and why the small sprocket you never look at wears first.
Reading the teeth
Healthy: symmetrical, evenly-spaced teeth with rounded valleys — hills in a row. Worn: teeth lean visibly in the drive direction, valleys stretch into a rampy profile. Done: hooked tips curling like a wave about to break, or shark-fin points where metal has thinned. Compare your rear sprocket's most-loaded face against a photo of a new one — asymmetry you can see by eye means the sprocket has been re-machined by a worn chain and is now returning the favor.
The front sprocket: worst wear, least seen
The countershaft sprocket is a third the size of the rear, so each of its teeth engages the chain roughly three times as often — while living inside a cover packed with chain-lube sludge that holds grit against it. It usually wears first and worst, and nobody looks because looking requires removing the cover. Pull it when you clean that cavity (the sludge-cave cleanup) and read those teeth too.
Why chain and sprockets are a set
A worn chain's pitch grows (measuring stretch), and the elongated chain bears on the sprocket teeth at the wrong points, machining them to match its wear. Fit a new chain to those adapted sprockets and the mismatch runs in reverse — the sprockets rapidly wear the new chain to their old pitch, which is why new-chain-only replacements keep going loose and die young. Replace as a kit, every time; the job is in the replacement walkthrough.
Aluminum, steel, and how you ride
Steel sprockets last longest; aluminum saves rotating weight and wears fastest — racer math, not commuter math. Combination rears (aluminum center, steel teeth) split the difference. Dirt use wears any of them faster; gearing changes are the moment to choose (the gearing guide).
The inspection habit
Sprocket reading takes ten seconds and slots into the cleaning routine you should be running anyway — teeth are easiest to read on a clean drivetrain, one more thing the CC360 minute buys you. Sprockets never wear alone: hooked teeth mean the chain is due too, so cross-check the full wear signs list before ordering parts.
Quick answers
What do worn sprocket teeth look like?
Healthy teeth are symmetrical hills; worn teeth lean in the drive direction, hook like breaking waves, or sharpen into shark fins. Any asymmetry visible by eye means significant wear.
Do sprockets wear out or just chains?
Both, together — the chain's stretched pitch re-machines the sprocket teeth to match. That's why chain and sprockets replace as a set.
Which sprocket wears out first?
Usually the front (countershaft) sprocket — it's smaller, so each tooth engages several times per chain revolution, and it runs in the worst grime.