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Chainring wear and chain suck: how to spot it before it costs you a drivetrain

By Crankworthy · Published · Updated

Chainrings rarely wear out on their own — a worn chain wears them, because an elongated chain no longer sits in the bottom of each tooth valley and drives on a smaller patch of metal instead. Measure the chain with a gauge and replace it at 0.5% wear (0.75% on older, wider drivetrains) and the rings last for years 1. Leave it, and hooked teeth and chain suck mean you replace the ring, the cassette and the chain together.

Chains do not stretch, they wear

Nothing about a chain is being pulled longer. The pins and the insides of the links wear away, each joint gains a fraction of play, and the chain gets longer as a result 1.

A new chain has a pitch of exactly half an inch — 12.7 mm from pin centre to pin centre, so an inner link plus an outer link measures one inch. Grit mixed with lubricant grinds material out of the pins and link bores, and that lost material shows up as extra length.

Once the chain is longer than the sprocket was cut for, it stops seating at the root of each valley and rides up the tooth faces. The same pedal force is now carried on a smaller contact patch, which is what transfers the wear from the chain to your rings and cassette. This is why the chain is the cheap consumable that protects the expensive parts — but only if you replace it on time.

The measurements that matter

Chain wear is measured as a percentage of elongation, and gauges read it directly [1][2].

New chain pitch
12.7 mm (half an inch) pin to pin; one inner plus one outer link measures 25.4 mm.
0.5% wear
The replacement point for most modern drivetrains. Park Tool’s gauges read this step directly [2].
0.75% wear
The replacement point manufacturers give for older, wider chains. Past it, the cassette is usually worn too [1][2].
1.0% wear
Well past replacement — expect to buy the cassette and probably the chainring with the chain [2].
What a gauge is doing
Contacting the chain in three places along a long section and measuring how much the pitch has grown [2]. Keep tension on the chain while you read it, or the number lies.

Reading a chainring by eye

A healthy tooth is roughly symmetrical. A worn one has the driving face scooped out and the tip leaning over it, and the giveaway is seeing that shape repeat across several consecutive teeth.

The face that carries your pedalling force wears first, so the tooth turns asymmetric — hooked on one side, still sloped on the other. One odd tooth is damage; several in a row is wear. Sight along the ring rather than looking at one tooth straight on.

Two more signs worth knowing. Teeth that have gone thin and polished bright let the chain rattle sideways on the ring. And on a multi-ring crank, the shift ramps and pins on the outer face wear flush with the ring body, which shows up as front shifts that hesitate or refuse to lift.

A worn ring also announces itself through a new chain. Fit a fresh chain to a badly worn ring and it skips under load, because the new, correctly pitched chain no longer matches the worn tooth spacing — the classic case of leaving the chain too long and paying for it twice.

Chain suck

Chain suck is when the chain fails to release from the chainring at the bottom of the stroke and gets carried up and round, jamming between the ring and the frame. It is a worn or damaged ring until proven otherwise.

Hooked teeth hold on to the chain a fraction longer than they should. Add a bent tooth, a dry or gritty chain, or a soft, cheap ring worn faster than usual, and the chain is lifted instead of released. On a frame with tight chainstay clearance it then wedges, which at best stops you and at worst gouges the stay.

Fixes in order: check the chain for wear and replace it if it is past the threshold; inspect the ring for hooked or bent teeth and replace it if several are hooked; keep the drivetrain clean and lubricated so the chain releases cleanly. On 1x setups, a clutch derailleur helps by keeping the lower run under tension.

Checking it properly

  1. 1

    Measure the chain first

    Use a wear gauge on a tensioned section of chain. If it is past 0.5% (or 0.75% on an older, wider drivetrain), the chain is the first thing to change 12.

  2. 2

    Look along the teeth

    Sight across the ring for hooked, asymmetric profiles repeating over several consecutive teeth, and for teeth that have gone visibly thin or polished.

  3. 3

    Try to lift the chain off the ring

    With the chain on the big ring, lift it away at the three o’clock position. A healthy ring holds the chain seated; a badly worn one lets it lift clear of the tooth tips.

  4. 4

    Fit the new chain and test under load

    If a fresh chain skips under hard pedalling, the ring or the cassette is worn past the point where a chain alone fixes it.

Chains and chainrings in the catalog

Match the chain to your drivetrain’s speed count, and the ring to your crank’s mounting standard.

What this job needs that we don’t stock

Named so you can source them elsewhere — we would rather say this than point you at a product that is not the right one for the job.

  • A chain wear gauge — the one tool this entire guide depends on is not in our catalog.
  • Chainring bolts and replacement shift pins for multi-ring cranks.

References

  1. 1.When to Replace a Chain on a Bicycle — Park Tool (how chain wear happens and when to act)
  2. 2.CC-4.2 Chain Checker — Park Tool (reads 0.5%, 0.75% and 1.0% wear; three-point measurement)

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