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I'm trying to figure out how the rear cassette is put together, and I found this related question that suggests at least maybe the lowest gears can be replaced. I'm trying to figure out if in general any and all of the cogs in a rear cassette can be swapped out with new replacements should any get damaged or worn? I imagine some may be designed to be an all or none deal, but if one's rear cassette supports replaceable cogs what would be the giveaway to do a visual inspection for?

This question is also distinct from Is it practical to replace two sprockets on a cassette? where the focus is on practicality of replacement but not so much of how to discover if replacement is applicable to a given cassette. It's also distinct by relating to the whole cassette in general with respect to all of its cogs.

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    They are all different, and there a a million variations. Many cassettes use a spider ofr the largest 2 or 4 cogs. Some combine the smallest few. Single cogs cost nearly as much as a new cassette, and cogs in a set are designed to work together. You rarely wear out just one cog. Cassettes are relatively cheap. This all adds up to it just not worth the effort to try. – mattnz Aug 22 '16 at 20:18
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    @mattnz why won't you write this down as an answer? – Alexander Aug 22 '16 at 20:24
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    In practice, you replace the whole cassette, even if some subset could theoretically be replaced on its own -- it's more time and money efficient (since you'd have to buy another full cassette anyway to get the replacement parts in many cases). People do make custom cassettes (Harris cyclery sells a few), but they're likely built by buying a bunch of cassettes, cannibalizing them and then putting them back together -- something not very feasible at home. – Batman Aug 22 '16 at 20:31
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    Possible duplicate of Is it practical to replace two sprockets on a cassette? – Móż Aug 22 '16 at 20:47
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    When people do not know the answer to your question, they talk about other things obviously. Why you want to change only one cog is your business and nobody elses. I hoped to find technical answer how to separate cogs for separate reason. Nada. And btw, cog wear is never even. People can ride for weeks not using the smallest or the largest cog. Let`s say in flat country like Holland. – Dragan Jan 31 at 20:46
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The way to check is to remove the lockring and see how much of the cassette has a carrier and/or how many cogs are individual. However, the situations in which this would be beneficial are few.

--You have very specific gearing needs. If you are a extremely serious rider and wish your cassette to be tailored to your power profile or something similar, replacing individual cogs may make sense.

--You have a very expensive cassette and have somehow managed to damage only one cog. In this case where some freak accident has damaged one cog, but the rest of the cassette is fine, it would make sense on a high end cassette to replace one cog.

Those are really the only two scenarios I can think of where such a replacement would be warranted. With proper riding cassettes wear fairly evenly and by the time any one cog is shot, you are better off replacing the whole cassette (and the chain). If you are riding badly and using one gear/cog all the time and have destroyed it, but left your other cogs magically untouched, you should probably consider less expensive components, better riding technique, a single speed or some combination of those three.

Keep in mind that many of Shimano's patents are related to tooth (cog) design and ramping. Replacing a damaged individual cog with the same one on an expensive cassette may be easy (second scenario), but changing the gearing ratio on a cassette (first scenario) may cause shift gate misalignment and ultimately sacrifice shifting performance for more individualized gearing.

  • This is probably the most comprehensive in relating to the various parts of the question, one the existence of individual cogs, which is hard to make out never having seen a cassette separated from its installation on the rim. This video showed me just how individual and grouped they can be; and two the relation of the Q to scenarios, especially in consideration to how those scenarios justify the labor and pursuit of parts. I realize now I'm in the "replace the whole cassette camp", but wasn't clear going into the Q. – jxramos Aug 23 '16 at 1:02
  • You also touch well upon a follow up question about alignment should one attempt an individual cog replacement. I wasn't sure if cassettes were patterned in some sort of angular phase shift arrangement, it sounds like the relevant concept in this area is "shift gate alignment". Cool stuff. – jxramos Aug 23 '16 at 1:04
  • That notion of a carrier is new to me too. I found a reasonable article depicting one of those fellas and it does a good job showing the cassette disassembled. Here's some good background they provide... Some cassettes will use a large 'carrier' that many of the cogs are attached to, turning them into a single unit, while some others may use separate cogs throughout the entire cluster – jxramos Aug 23 '16 at 1:27
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According to the late great Sheldon Brown, yes you can change an individual sprocket in a cassette, at least for Shimano. Some cassettes have small bolts or rivets holding the gears together, but this is for convenience.

Most Shimano cassettes made in the '90s or later have a feature called Hyperglide (probably a registered trademark) that enables smoother shifts, by allowing the chain to engage two adjacent sprockets simultaneously. Hyperglide works by giving each individual tooth a more complicated shape to facilitate shifts to and from each sprocket. In order for Hyperglide to work, the adjacent gears have to be carefully matched to each other. So if you change a sprocket for another sprocket with a different number of teeth, then shifts to and from that sprocket won't be as smooth. But as Sheldon pointed out, that's what everyone was used to for decades before the invention of Hyperglide, so that needn't bother you.

I haven't been able to find anything on Sheldon's site about changing sprockets for Campagnolo or SRAM, but I would assume that those brands shape their sprocket teeth similar to the way Shimano do, and so similar concerns must apply for those brands also.

Personally, if a few of the sprockets in my cassette were worn, I would just change the whole cassette (and the chain also of course). You're unlikely to save any money or hassle by just changing one or two sprockets, because the vast majority of bike riders change the whole cassette. Most people who want to change just one or two sprockets want a particular combination of gear ratios for specific reasons.

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They used to be, but unless you're using something weird like Miche cassettes, they're not really available new anymore.

The best giveaway to measure wear is how it does with a Rohloff HG/IG checker. Second best is whether its teeth are blunted and smooshed at the roller contact area.

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