# when is a cassette worn out? how can I tell?



## oatmeal (May 7, 2007)

I took out an old cassette from my parts bin when I was doing some cleaning, and decided to clean it up. It looks fine to me, but I'm not sure what to look for as far as wear. is there obvious tooth deformation on a worn cassette? I can't remember the mileage on this particular one, but it is a dura ace cassette, which I understand is not as durable as (say) an ultegra.


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## aaronbarker (Aug 31, 2005)

you should look for deformation of the teeth - especially if you know which side was driving against your chain. if you install it, the one sign i've experienced is the chain 'jumping' on the worn cog when you start to put significant pressure on your drivetrain. there may be other signs, but those are what i'm familiar with.

have fun,
aaron


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## MR_GRUMPY (Aug 21, 2002)

The only way to determine if you cassette is worn out, is to install a new chain. The chain will skip on your most used cogs, when you pedal hard.


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## Eric_H (Feb 5, 2004)

*New chain test*

Mr. G is correct, put on a new chain and test you most-often used cogs under load. Use the little ring, ride uphill and pedal hard in each cog. If any are "worn out" they will skip. A perfectly functional cassette will often show some wear and deformation on the most-used cogs but still pass the chain-skip test. And yet another cassette that looks to the naked eye to be similarly worn will skip with a new chain. Truth is that it is pretty hard to tell visually when a cog is worn out.


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## Oldteen (Sep 7, 2005)

One other thing to look for is chipped plating on the teeth of your most-used cogs. Many current cassettes are plated, and the chains wears through the plating.


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## Kerry Irons (Feb 25, 2002)

*Chipping away*



Oldteen said:


> One other thing to look for is chipped plating on the teeth of your most-used cogs. Many current cassettes are plated, and the chains wears through the plating.


Chipped plating can happen in the first 100 miles, or the first 1000 miles, and it does not mean that the cassette needs to be replaced.


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## Oldteen (Sep 7, 2005)

Kerry Irons said:


> Chipped plating can happen in the first 100 miles, or the first 1000 miles, and it does not mean that the cassette needs to be replaced.


I still figure it could be an indicator of weakening cogs &/or the little plating chips can be working their way into the chain. Few years ago I noticed chipping when cleaning an 8sp MTB cassette- which then broke a tooth on the same cog within next 200mi or so. Coincidence??? Perhaps I am indeed wasting $$ by replacing cassettes too soon, but it somehow makes me feel better. Just replaced a SRAM 950 cassette @ about 6k mi with plating chips, but it was also skipping under load (even with freshly lubed chain) so sounds like others would have replaced this one too.
FWIW- I realize I have nothing like your (Kerry's) experience, but I've not seen such chipping on a quality 9 or 10sp road cassette with less than 2-3 thousand miles. This is on Shimano 105/Ultegra and SRAM 950-970 level cassettes with well-maintained Shimano or SRAM chains. On my MTB's the only time I've seen this on a newer cassette has be along with crash or rock damage. 


A somewhat worn cassette may have deteriorating shift quality before it starts to skip. To some it's worth replacing the cassette at that point.

I agree it's hard to tell worn-out cogs just by looking, although cleaning them and comparing with new of the same brand can make wear easier to spot. I've never replaced a cassette by visual inspection alone, though.


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## C-40 (Feb 4, 2004)

*why teeth break...*

Here's some info from Jobst Brandt about chain and cog wear. I've also posted quite a bit on chain wear, including my scheme to alternate the use of three chains to avoid mating a new chain with worn cogs. I hope to get 10-15,000 miles from a cassette, but I may encounter excessively hooked teeth before I get to 15,000. What's not covered in Brandt's writing is the fact that some chains (current Campy models) have such hard pins that they may show little elongation, even after 6,000 miles. That doesn't mean the chain isn't worn out. A check of the distance between rollers and side clearance will show an extremely worn chain that still has a pitch that's well within tolerance. One of my chains in this condition wore out one steel cog in 6000 miles. Another wore out two Ti cogs in only 4000 miles. This proves that monitoring chain pitch won't guarantee that the cogs are still useable with a new chain. Thes cogs will still work fine with a chain that has even a few hundred miles of use, but not a new one.

The small chainrings on an MTB increase chain tension and the chances of breaking teeth.

From Jobst Brandt:

Chain life is almost entirely cleanliness and lubrication related
rather than load related. For most bicycles the effect of load
variations is insignificant compared to the lubricant and grit
effects. For example, motorcycle primary and timing chains, operated
under oil in clean conditions, last years while the exposed rear
chains must be replaced often.

The accurate way to test whether a chain is worn is by measurement. A
new chain has a half inch pitch so that it has a pin at exactly every
half inch. As the pins and sleeves wear, this spacing increases and
becomes damaging to sprockets. When the chain pitch grows over one
half percent, it is time for a new chain. At one percent, sprocket
wear progresses rapidly because this length change occurs only between
pin and sleeve so that it is concentrated on every second pitch. The
pitch of the link containing the rollers remaining constant. By
holding a ruler along the chain on the bicycle, align an inch mark
with a pin and see how far off the mark the pin is at twelve inches.
An eighth of an inch (0.125) is a little over the one percent limit
while more than a sixteenth is a prudent time to get a new chain.

Skipping Chain

That a new chain does not want to engage used sprockets may be
obvious, but in theory a new chain cannot freely engage a new rear
sprocket under load even though it has the same pitch as the chain.
That is because the tooth being engaged would be under load and this
is a contradiction in itself. Therefore, a slightly worn sprocket,
that has pockets in its load bearing face is even more reticent to
engage a new chain with perfect 1/2 " pitch. 

Sprockets, by the way, do not change pitch when they wear, only the
tooth form changes because the number of teeth remains the same and
the base circle remains essentially unchanged for normal sprocket
wear. On fixed gear bicycles that are ridden until the chain is 5%
out of pitch, the base circle may be slightly reduced but this only
makes the fit of a new chain worse.

Without a strong chain tensioner or a non derailleur gear, the chain
has insufficient tension on its slack run to engage the sprocket when
under tension. In contrast, engagement on the tension side, as on the
crank sprocket, generally succeeds even with substantial tooth wear
because the tension encourages engagement. This condition, however,
enhances "chainsuck", the failure of the chain to disengage the
chainwheel. This can generally not occur without a long arm
derailleur, common to most MTB's and therefore, road bicycles normally
experience a grunchy disengagement instead of a chain jam.

A new chain has a pitch of exactly one half inch. A sprocket, worn by
a longer pitch (worn) chain, has hooked teeth but with the correct
pitch. The hooked profile is formed by the rollers of a worn chain as
they exit the sprocket under load, whereas rollers of a new chain with
correct pitch exit under no load because the load is transferred to
the next roller before disengagement. However, with hooked sprockets
the new chain cannot engage under load because its pitch doesn't allow
it to get over the hook and into the next pocket. These differences
are only a few thousandths of an inch but enough to prevent engagement
when the previous roller is fully engaged.

As a chain wears it concentrates more of its load on the last tooth of
a sprocket before disengagement because the chain pitch no longer
matches the pitch of the sprocket. This effect sometimes breaks off
sprocket teeth. The load concentration on the sprocket also
accelerates wear and is another reason to replace a chain at 1/16th
inch wear.

Jobst Brandt


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## deef (Aug 19, 2003)

Ummm...an eight of an inch would be 12.5% .... way over the 1% limit.


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## HammerTime-TheOriginal (Mar 29, 2006)

No. That's 1/8 / 12 is approxiamtely 1%. You missed the part about doing it over 12 inches.


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## spastook (Nov 30, 2007)

Years ago whenever I'd buy a new freewheel(dating myself here) I'd buy 3 new Sedisport chains to go with it.First of each month I'd slap on a new chain. By rotating chains I'd get a ridiculous lifespan out of the freewheel. Today with cassettes often costing 100- 300 dollars and chains 30-60 buying 3 chains gets very expensive but with cogsets as expensive as they are it's still a money saver. But as stated previously, you'll know they're worn out when the chains starts skipping over cogs.


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