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I measured my chain last night - 10 links were 25.8-25.9 cm. So I ordered a new one, tools and spare link pins (Shimano 8-speed HG). I'm thinking this amount of wear might explain why my least favourite gears feel and sound not quite right, while the ones I use the most are fine (i.e. the favourites are worn with the chain).

A new cassette isn't much money, but changing the cassette makes for a much bigger job, and I'd have to buy the tools. As it is, it's the first time I'll have fitted a new chain.

The bike probably has 2000-2500 miles of mostly tarmac, just enough dirty stuff to get grit everywhere, taking ~100kg up some reasonably steep hills.

EDIT: The difference between my question and this one is that the old question doesn't say anything about amount of stretch (though the answers there would tend to suggest the bigger job)

EDIT2: I finally got the chance to get a photo in daylight. I don't like the way the chain is sitting (at the top) on the sprocket it's meshed with, though the 11 and the 32 are better than I thought -- I overlaid the image of the teeth of the 28 (little used) on the 32 (works quite hard sometimes). enter image description here

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Your local bike shop should have a tool for measuring the wear on the cassette. But at 2000 miles your cassette is unlikely to be badly worn -- I tend to expect closer to 5000 miles from a cassette (though running with a worn chain will wear one out faster). –  Daniel R Hicks Nov 13 '13 at 12:02
    
You could post a picture of the profile of the cogs. –  Vorac Nov 13 '13 at 12:33
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Don't worry about the effort involved, both changing the chain and removing/replacing the cassette are trivial - 5 minute jobs. Sounds like you researched swapping chains already but for the cassette you just need to make sure you buy the correct lockring remover (Park Tools offer an exhaustive selection) and a decent wrench. To be honest if that were my bike, even if I'm not replacing the cassette, I'd be taking that one off to give it a good clean. Make sure you put it back on nice and tight, its something like 40Nm if memory serves. –  PeteH Nov 13 '13 at 20:03
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@PeteH - And don't forget the bustier and garter belt. –  Daniel R Hicks Nov 14 '13 at 1:08
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@DanielRHicks - had to look that one up, praise the lord for Google Images! –  PeteH Nov 14 '13 at 10:10

3 Answers 3

up vote 3 down vote accepted

The easiest way to tell is simply to install the new chain on the cassette. If the cassette is worn from the old chain, it will skip when you apply a decent amount of pressure (standing up will usually do this in your big ring and half way down your cassette). If it does jump, you'll need a new cassette. It's really as simple as that.

I would be surprised if you need a cassette. The lower model cassettes are made of steel and don't wear easily. (My current cassette, a Shimano 6700 is now 12,000 miles. I change chains about as often as you did and I do keep it well lubed).

You may notice a bit of noise when you change chains. I notice this also and it usually goes away after some mileage. If not, you can always try adjusting your rear derailleur a bit to see if that helps.

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I've accepted this one as it's the first to make the point that try-it-and-see is a feasible and the simplest idea. But thanks and +1 to everyone. –  Chris H Nov 14 '13 at 9:14

The cassette looks worn to me. The best indicator that a cassette is worn is that the teeth are asymmetrical. Check out Sheldon Brown's site for a detailed discussion about chain stretch and sprocket wear.

There's no magic ratio that if a chain is worn x amount, the cassette will be worn too. There are too many factors involved, the material that the cassette is made out of, whether you're a masher or a spinner, what gears you ride in the most (smaller rings wear more easily), etc.

As you have guessed, it is likely that your favorite gears have stretched with the chain and that's why you're noticing some problems on the gears that you use less.

As Rich mentioned, you can install a new chain and see if it skips. If it does, you definitely need a new cassette. If it doesn't, you might be able to get away with that one for a little while longer.

And as Pete mentioned, replacing the cassette is not a large job. I personally find replacing the chain to be more frustrating because the dang thing wants to fall off. As far as the tools go, I'd buy a cheap tool kit similar to this one. But shop around, you may be able to find a better deal. I didn't dig too much. Whatever you find, it's not going to have the best tools, but they'll certainly be good enough to get you started and keep you going for a long time. I bought a similar one about 15 years ago and still use many of the tools. In fact, it contains the only chain whip and cassette tool that I own to this day.

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+1 The cassette looks worn to me. –  andy256 Nov 14 '13 at 6:30
    
I think this wins in the end - I changed the chain at the weekend, and the new cassette and tools are now on order - my most used sprockets skip like mad under even light load, especially on the middle chainring. However despite liking the look of the toolkit I won't be taking your advice on that, too much duplication with what I've already bought. –  Chris H Nov 18 '13 at 10:17

To me, the smallest cog looks worn and the 2-3 only a little.

This could be a nice way/moment to teach yourself to ride in high cadence (by avoiding those gears, which you have been obviously abusing)!

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When you say 2-3, do you mean 2nd/3rd smallest? I certainly don't use the 2nd smallest much, but do use the 3rd/4th/5th smallest quite a lot. Then I don't use the next 2 very much, finally the largest gets some use. –  Chris H Nov 13 '13 at 15:04
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@ChrisH, yes, second and third smallest look asymetrical to me. However, I have next to no experience with servicing cogs. This answer is more of a ... way to move the chatty discussion away from under the question. Let's see how many people agree and how many disagree with the statement :) –  Vorac Nov 13 '13 at 15:13

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