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Due to sheer laziness, my maintenance amounts to an annual trip to the LBS. After moving, my new LBS suggested that I replace my chain immediately, before it destroys the drive train. What they didn't mention was that it already had, so I needed a new cassette within a week, because the chain slipped under pressure.

The next year, they checked the cassette before recommending a chain replacement, and it was already getting worn, so I decided to stay with the current chain at least as long as it takes to pay for a new cassette in the chains I'm not purchasing every thousand miles. At about three thousand miles a year, it shouldn't take all that long.

Now, though, I'm concerned that I might be causing more problems than just cassette wear. Might I have to replace the chain ring, too? Am I setting myself up for other potentially expensive problems? Is the chain likely to break in the middle of a ride within the next year or two?

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up vote 16 down vote accepted

This is always a controversial topic, with some people arguing on both sides, but in my opinion you should replace your chain when it reaches the official "worn" state (as indicated by a chain stretch gauge). If you let the chain go the sprockets develop a "hook" and will begin "sucking" the chain. In addition, shifting performance will suffer.

If a chain is replaced when it first reaches "worn" status, without letting it go too long, the sprockets will not have taken a "set" to the stretched chain and reasonably good drivetrain performance will be retained.

Failing to replace a worn chain results in more cluster wear, more chainring wear, and an increased risk of both shifting difficulty and thrown/broken chains.

You will of course eventually need to replace your cluster and chainrings. My experience is that you need a new cluster about every five chains, and new chainrings about every two clusters. Generally when cluster/chainring wear reaches a critical point things go to pot pretty rapidly in terms of shifting problems, slipping, etc.

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Thanks; I'll be watching for the sucking and shifting problems, then. Whether that really convinces me to replace the chain thrice a year is still up in the air, though. – eswald Nov 5 '11 at 21:48
All true. That said, it doesn't mean your cassette teeth and chain ring will not wear, only that they wear slower. I average about 5 chain swaps between cassette and chain ring swaps. At least 1000 miles per chain, although Shimano says change it at 800 miles.. – zenbike Nov 8 '11 at 4:36

The worst problem I face when waiting too long to replace a chain is that a new chain will skip badly over the worn sprockets.

In my experience, it has a lot to do with the kind of terrain you ride (on- vs. off-road), the amount of rain/mud/snow you take, and if your have full fenders or not.

If you do mountain bike, 500 miles is sometimes enough to need a chain replacement. 1500 miles will for sure damage your sprockets permanently. Now if you ride only asphalt, use full fenders, and take proper care on cleaning and lubing, you might go over 3000 miles without much problem.

I agree with a previous answer, it takes three to five chains to need a cluster replacement if you care well, but the chainrings use to last much longer to me than two clusters. I think it is because, when you install a new chain, the wear pattern on the teeth (both the sprockets and the chainrings) tend to get back to normal (wear occurs at the base of the teeth, instead of their tops). Since the rings wear much less than the sprockets, they go back to normal more easily, and have a much lesser tendency to skip.

It is worth mentioning that I had never experienced a chain braking because it was worn out, so the problem is not dangerous, just expensive (because you have to replace two or three parts instead of one), not to mention the bad ride quality due to worn-out drivetrain.

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A slipping chain can be dangerous even if it doesn't break: on one bike I'd never changed the chain (it now also needs the sprockets and the chainrings replacing) and one slip did cause me to fall off... – Hugo Nov 5 '11 at 22:15
Yep, slipping, jambing, or jumping off are all dangerous in the wrong circumstances, almost more so than outright breakage. – Daniel R Hicks Nov 6 '11 at 20:22

Not really an answer, but too long for a comment.

I've gone the other way - my second hand road bike has worn/munched big and middle chainrings, and the cassette is pretty worn too. Chain is unstretched with surface corrosion, and the master link popped under load yesterday.

So my plan is to run the entire transmission into the ground, and buy new rings/cassette/chain/jockey wheels all at once. There's no point replacing one thing with new when other parts are approaching terminal.

A road chain is good for ~3000 km / 2000 miles before it starts wearing into the cassette, whereas most chainrings are good for "the life of the bike" or 20,000 km

A worn cassette and worn chain can do more than 3000 km, but they need replacing together. MTBs off road will wear quicker.

I log every ride with strava, so it will be interesting to see how long this setup can go for before shifting and chain jump get too bad.

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