I have heard often that you should replace a worn chain, that a chain lasts somewhere between 800-1200 miles, and that if you don't replace the chain on time, you'll need to replace the cassette when you get a new chain.
My question is this: instead of going through 4 or 5 chains between cassette replacement, what is the downside of riding the same chain until the cog needs replacement? And, if you do that, how long would you be able to do so?
The cost of replacing worn parts is one part of the issue with excessive chain stretch, safety is another component.
This type of problem will take a while to emerge, but if you are going to run the drivetrain into the ground, at some point your safety may be compromised. Excessively worn chains may break, or skip over excessively worn gears. At some point you can wear the gears so much you can shear the teeth right off.
If this happens when riding out of the saddle (e.g., accelerating hard or climbing) you can actually be thrown off the bike and into traffic, crash and hit your head, crash your sensitive bits into the stem, or otherwise be embarrassed. The list goes on.
Will this actually happen to you? Who knows, but you should know that it is a risk.
If you let the chain wear excessively you will at some point have to replace:
Chain rings alone can be the cost of 2-3 chains depending on the quality of rings you go for (more if you have a triple chainring). Cassettes usually cost the price of about 2 chains. Let's put the price of derailleur pulleys at 1 chain (this is up for debate). And a chain costs the price of 1 chain.
That brings the total cost of a drive train to 7 chains. You would therefore need to get about 6000-8400 miles out of your single chain before the economics start to be in your favour. Do you think you can do it or will the chain break and become a mangled unusable mess? When that happens you are stuck replacing everything. Even if you hit 6000-8400 mark, how far beyond it will you get? Only after 8400 miles are you starting to save.
Also don't forget that a really worn drivetrains shift horribly so you will also need to factor that into the cost somehow. Is a louse experience worth saving a few dollars? Only you can answer that question.
The only place where this strategy might work is for single speeds as cogs and rings are relatively cheaper and shifting is a non-issue.
How long a single chain or cassette will last depends heavily on the riding conditions. For example, do you weigh 50kg or 150kg? Do you ride a road bike in fair weather, or a touring bike on salted snowy roads?
If you're of average weight and riding in decent weather, you may find a single chain can last several thousand miles before it should be replaced. But you don't need to wonder, you can measure!
Get a chain gauge like the Park Tool CC-3.2, and you can quickly measure your chain in a repeatable manner. Or you can use a ruler, if you don't mind a bit more fiddling.
Once the chain is worn beyond the recommended amount, you should replace it to avoid undue wear on the cassette. However, you are right to observe that you could also "ride it into the ground," replacing the chain and cassette only at the last moment when they are no longer functioning properly. You'll probably need to replace at least one of your chainrings (up front) then too, but that's OK. You won't save money this way though, because the chain is the cheapest part to replace. And you'll likely end up breaking your chain (because in this line of thinking, why else would you replace it?). Having a chain break while riding is not only inconvenient, it's dangerous.
Thanks for the comments. I am relatively convinced, but, I have to say, almost all the comments about the downside seem to come from people who haven't had those things happen to them. And if someone did have a chain break, how long or how many miles did they put on them?
On my part, I've ridden some 150,000 miles over 30 years (5,000-6,000 miles a year), and have never had any of the horribles happen to me - - though, admittedly, I've never pushed a chain or cluster all the way to the limits. Nor have I ever heard of anyone even having to replace the chainrings. And, I've ridden up and down hills and mountains (live in the San Francisco Bay Area), in good weather and bad, and ridden aggressively and on multi-day tours. I've let some chains go for much longer than recommended, and, only when I change a chain do I get any negative symptoms.
For example, why would the rear cluster gears, which get used most, wear so fast, when the chainwheel, which only has 2 or maybe 3 gears, never seem to wear? And, I never have trouble with the chain at anything like 1,000 miles - - except I have to change the cluster if I don't change the chain by about that point.
By the way, I measured with a Park CC-3 or whatever, and my chain sat between .75 and 1.0 or whatever the upper measurement is. I put on a new chain, and the highest gears now skip (even though the middle gears on the cluster are the ones I ride most often). Admittedly, the tool is the old version of the chain measurer that Park has . . . guess I'll just break out the ruler from now on.
The way I figure it, if the cost of a cluster is about twice the cost of a chain, you'd have to go through the equivalent of missing two chain changes to come out equal. Also, if you can buy chains off-season at reduced prices, the same holds true for clusters. The biggest trouble is finding the spot where your ride doesn't start deteriorating . . . has anyone ridden a chain so long the shifting isn't very good, or it starts skipping from wear? Also, I have to take the cluster into the LBS for service because I have never mastered switching clusters.
Thanks again, not arguing, just trying to get at the truth.
John
If you replace the chains early, you can get way more than 4 or 5 chains per cassette. A chain is about the cheapest part to replace on a bike and it's certainly the cheapest part of the drive train.
One of my bikes has had the same cassette since at least 2006, that cassette has over 10K km on it and it shifts like brand new with almost no signs of wear. I'd guess it's been through somewhere around 15 chains. I replace my chains as soon as they show any wear with the Park CC-2 chain gauge. ( New chains generally read 0.5, I replace them at 0.75)
If you are using standard low end cassettes than you can get for $50, this kind of care may not be worth it. However, I have a custom cassette (14-30) that I cobbled together Sheldon Brown style, this would be relatively expensive and difficult to replace.
If you ride the chain/cassette into the ground together, it's going to get progressively worse until either the chain fails or the teeth on the cogs snap off due to wear. You won't get anywhere near 10K km. Having a chain break can sometimes lead to injuries.
Once the chain starts to wear, it essentially grinds on the gears with every pedal stroke; the whole thing goes downhill quickly. If the chain shows wear at 800 miles, you'll start having problems at 1000 miles. How soon you replace things after that depends on your tolerance for an imperfect drivetrain; the problem is that the gears do not wear evenly. The least used gears stay at the "old" chain spacing and get harder and harder to use over time.
You can often get away with not replacing the chainrings when you replace a worn cassette, but if you really run it into the ground, you may have to replace at least the smaller chainring as well. In particular, the smallest rings on a triple can be quickly destroyed in just a few days of riding with a worn chain.
Instead if you pay attention to the chain wear, buy chains on sale ( $20 at the end of the summer. ), you'll have a gear train that works as good as new it's whole life. I fully expect to get at least another 10K km out of that cassette and the chainrings should likely last as long as I ride that bike.
You can probably argue the economics either way, I don't include the cost of my time in dealing with chain maintenance. And while I spend more on chains than most people, I spend a lot less on cassettes and chainrings. It comes down to how much you enjoy working on bikes, having well working shifting and how long you plan to keep the bike.
I don't know, I have done some 5k miles on my second hand bike (I assume chain already had miles on it) since I bought it a year ago and it shifts well and I hadn't even thought of chain replacement before... I live on a hill and I change gears quite often.
One alternative is to purchase a stainless steel chain such as the Wipperman Connex, which will last a very long time, but will no longer be the cheapest part of the drivetrain. Most everything has been covered in previous answers (really good thorough answers too. Shouldn't you people be out riding or fixing bikes or something?). I would just add that it's not worth buying good parts if you're not going to take care of them. If you don't replace you're chain, you're going to walk into your shop one day and they're going to say, "You need to replace your entire drivetrain." or any new chain you put on is going to skip like a little girl on her way home from school.
