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I took my bike to the mechanics the other day and along with needing my chain replaced they said that I also need my cassette changed and the front cogs.

I was wondering how long I can ride my bike now with a worn cassette before it becomes unridable? The teeth on the cogs seem a bit worn but they are nowhere near as bad as what I have seen on other videos.

What can I expect to happen when the cassette does start to fail? Gear slipping? Crunching sounds?

  • Did the mechanic measure the chain wear? There's a point at which a chain is so worn that there's no point in replacing it alone. If it is still running happily on the gears, the gears will also be excessively worn and a new chain will slip. Ideally, obviously, it's best to catch it before that point and replace only the chain. There's a temptation to leave it alone as long as it's working, but then you run the risk of a sudden chain failure. Basically, it depends on how much you trust the mechanic's advice. – JHCL Aug 23 '16 at 10:51
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    A cassette is too worn if a new chain skips on it in your favourite gear. Before that it might soften the life of your new chain. – Chris H Aug 23 '16 at 11:43
  • Skipping, "catching", and failing to shift reliably are the symptoms. Until one of those becomes a problem or the chain simply falls off you can continue to ride. However, the worn cassette may not play well with a new chain and will cause it to wear out prematurely, and the worn chain will accelerate wear on the front chainrings. – Daniel R Hicks Aug 23 '16 at 11:50
  • It should be noted that, had you replaced your worn chain more promptly, you would have gotten more wear out of the cassette. – Daniel R Hicks Aug 23 '16 at 21:04
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In my experience, skipping in certain gears at the rear is the first sign. Usually in the most used sprocket.

Then the chain becomes worn - and perhaps starts to snap - and when you order a replacement - it skips all over the place because it is being run on an overly worn drive-train. You might be able to salvage the old chain and run it for a bit longer - but sooner or later - you have to bite-the-bullet and buy complete new drive-train.

But if your current drive-train is happy and not exhibiting any malfunction (keep that chain clean and oiled) - you could go for many many many miles on it.

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    Fits my experience. Generally, it is recommended to change the chain when it visibly elongates -- that extends the life time of the more expensive drive train parts. I have heard recommendations to always change the cassette with it; not sure about that. If all parts need to be exchanged anyway there is no reason (apart from less exact gear shifting, perhaps) not to continue using them to the point of failure, which is slipping, as you described. – Peter - Reinstate Monica Aug 23 '16 at 13:36
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    The only real risk, in my opinion, is that eventually the chain will start skipping over the teeth in the most worn ring (either in the front ring or the cassette). Until that happens things should be fine, but once that starts to happen, don't delay in replacement. Trying to accelerate across a busy intersection when your chain suddenly starts 'free-wheeling' is not something you want to experience more than once. – Penguino Aug 23 '16 at 23:27
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The first sign is a very slow degradation of performance and an increase in friction. You'll not notice this over time, its only when fitting a new chain that the difference is clear.

Bad and slow shifts slowly increase, as does chain noise.

You can either run the whole transmission system in to the ground, and replace cassette/chain/ 2xjockey wheels and the chainrings, or you can change the bits that are worn while getting more mileage out of the chainring.

Be advised that chainrings are stupidly expensive, and a cheap big single chainring costs more than a cheap cassette.

The Jockey wheels are surprisingly important - if yours wobble side to side, consider changing them out too (they're relatively cheap)


Separate matter - if you have doubts about your LBS and their advice, just ask another one. Nothing wrong with a second opinion.

Some people just want their bikes to work (top efficiency is not that important) and other people want best efficiency at all times even if it costs more.

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    If the chainrings are riveted to the cranks, the whole crankset is about twice the price of a cassette round here. Standalone chainrings tend to be from higher-priced series. By leaving the chain for too long I've had 1:2:4 cranksets:cassettes:chains in around 20 000 km. On the low-end stuff I run, the jockey wheels aren't worth replacing - I changed the whole rear derailleur when it got loose, at the same time as the crankset (comment mainly to OP to give an idea of numbers) – Chris H Aug 23 '16 at 11:42
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I found the answer to your question the hard way, many years ago when I was an impoverished college student riding a cheap BSO that I got from another penniless student. It's been so long that I don't remember minor details, but surely the chain chattered a bit, but at the time I didn't think anything of it. Anyway I jumped on the bike and stood on the pedals to take off quickly; the chain ripped four or five teeth off the rear sprocket in an instant, and I was so unexpectedly unbalanced that I flew right over the handlebars. I ended up with some impressively-large road rash spots on my forearms, washing the gravel out was painful, and the bruises hurt too. I couldn't rest my arms on a desk for about five days until the road rash scabbed over. Interestingly, the chain didn't break.

I advise you to ride the bike very gently until you can replace the chainrings, cassette, and chain, or get yourself a better bike.

  • I did this in traffic once. The folks on the tram that narrowly missed running over me got a very spectacular view of someone doing a somersault over their handlebars for no apparent reason, and I learned to keep my chain in good order. – stib Aug 26 '16 at 6:59
  • Hi @stib, I'm sorry to hear that it happened to someone else besides me, but I also take comfort in knowing I'm not the only one ;) – rclocher3 Aug 26 '16 at 16:02
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First of all make sure that the bicycle mechanic actually measured the chain using the special chain wear measurement tools. If it is worn badly, it must be changed. I have heard stories about people who had serious injuries because of broken chains.

Even if the chain is worn badly, it may be possible that a new chain will work just fine. You should simply change the chain first. If you have problems changing gears or chain skipping with the new chain, you should probably change the cassette also.

As you can imagine the smallest rear cog usually wears much more, simply because same tooth contacts the chain much more often and it has to transfer more force. Sometimes you may get away with changing the derailleur limits so it wont use the smallest cog. (if you want to save money) Because new chain most probably will skip on the smallest cog.

  • If he were to remain with same worn cassette for the time being (more expensive option in long run as mentioned), I'd advice against changing the chain - the new chain will cause extra damage on worn cassette and itself, until they come in equilibrium again. – Matija Nalis Aug 25 '16 at 11:45
  • This assumption is incorrect. The new chain would avoid further wear. Because it will actually fit better to grooves instead of grinding the only tooth it is touching because of length increase. Especially since smallest cog will be worn most and he already mentioned it doesn't look so bad, it would be best to change chain and then limit derailleur to not use smallest cog. – Evren Yurtesen Aug 25 '16 at 11:56

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