Simple guide to worn rear cassette

[Sweep]

Am sure that this must have been covered before, at least with folks' individual pics of cassettes they are concerned about.

But for simplicity can some kind soul/s point me at a simple online guide with good pics that tells you how to identify a cassette that is worn and needs changing?

Am pretty up to speed on chains and front rings I think but have never been to sure about what to look for on cassettes.

Being a meanie, would hate to think that I was binning them too soon.

[rmurphy195]

If you are like me you probably use some cogs more than the others- so when you look at it, the ones you use a lot will look quite different to the rarely-used ones !

[Brucey]

if a cassette is very badly worn you can usually see it by eye. If the chain has gone past 0.75% wear then it is almost certain that at least one of the sprockets is now too worn to accept a new chain. If the chain is worn less than 0.5% then you would have to be rather unlucky to have a problem with a new chain on any of the sprockets. If the chain is worn between 0.5 and 0.75% then it is pot luck, and very difficult to tell if you will have a problem or not, not without trying it anyway.

The reason it is difficult to tell is one of tolerances. A chain link that has worn 0.5% has worn by 0.0635mm, i.e. 0.0025", as will a sprocket that has worn to match it. Short of trying a new chain, it is virtually impossible (using readily available tools) to see if a given sprocket has that amount of wear or not. In fact if the sprocket teeth are out of shape by just 10um more than a certain amount then it can cause the chain to skip.

cheers

[thelawnet]

Not sure there is one - I this week changed two chains. One is on my wife's bike and gets little force through it, though regular use. Replaced chain, all good. (3x8 mtb hybrid drivetrain)

Second was on my son's bike with road gearing, he is pretty strong and as soon as the chain was changed it was jumping in the 17t sprocket.

So went off to Decathlon and bought a new cassette (12-25 8 speed). The original was a Sunrace, on a Microshift drivetrain, but now they have Microshift branded cassettes, so that was slightly novel. Hg50 off the internets would have been slightly cheaper but I don't suppose it matters much

I.e. I think you either change the chain promptly (both chains were over 0.75%) or not; if not, the cassette may need replacing as well, but I'm not clear if there is a better way than trying it out.

[Brucey]

FWIW there is a tool which is sold for this purpose; the Rohloff HG/IG checker



the idea is if you lean on the handle, and see if the last link engages easily with any given sprocket or not, you can assess if the sprocket is so badly worn that the chain will skip or not. Which is fine except that the 'reading' is sensitive to both the load on the tool and exactly how the chain on the tool compares with the chain you intend to use. In practice this sort of approach doesn't remove the need to try it out sometimes, but it does help.

cheers

[CJ]

FWIW there is a tool which is sold for this purpose; the Rohloff HG/IG checker



the idea is if you lean on the handle, and see if the last link engages easily with any given sprocket or not, you can assess if the sprocket is so badly worn that the chain will skip or not. Which is fine except that the 'reading' is sensitive to both the load on the tool and exactly how the chain on the tool compares with the chain you intend to use. In practice this sort of approach doesn't remove the need to try it out sometimes, but it does help.

cheers

Yes I've got one of those too. As much use as a chocolate teapot, but it looks so shiny and Rohloff went to so much trouble to make it that I don't have the heart to throw it away.

[fatboy]

If it jumps with a new chain it's worn is my approach. I find that at 0.75 as per Park Tool I find the cassette should be fine for several chains. That cannot be said for Zicral chainring (middle one) which seems to only last me one chain (Shimano steel rings last much, much longer).

[Mick F]

Cassettes don't wear, it's sprockets that wear, usually the smaller ones.
The most used ones will wear sooner.

Fit a new chain and select each sprocket. That will tell you which one (or more) is worn.
Buy the individual sprockets as required.

I'm on my third 11t small sprocket. The rest of them are fine.
https://www.bike-discount.de/en/buy/shi ... 31?lang=en

[horizon]

Please shoot me down on this if required:

1. The problem with worn sprockets is that they will make the chain slip.
2. Chain slipping is annoying, inefficient but, most importantly, noticeable.
3. If the chain slips it is time to replace the socket.
4. The chain won't slip (as a result of wearing the sprockets) if it is changed regularly before it is stretched over the limit.
5. A new sprocket is wasted if used with a worn chain - so the chain must be good.
6. If, like me, you let things go on far too long, you just change the sprocket and chain together.
7. But only when it begins to slip (which you will notice).
8. Because the price of the socket and the price of the chain are similar.
9. And it therefore isn't worth the price of the chain to save the sprocket.
10. Especially when you've pushed both to their limits.

[Brucey]

depends how cheap your chains are really; if you shop around and pounce on good deals when you can find them a basic-but-OK KMC chain (Z8-S) can be had for five or six quid. It is worth taking those off at 0.5% and then (if you can't bear to throw them away) maybe using them again (on a more-worn cassette) from 0.5% to 1.0%.

FWIW if you wait until a worn transmission actually slips it is probably costing you in terms of reduced efficiency, not to mention chainrings.

Note that in terms of stuff lasting longer, you should aim to use as big a chainring and sprocket as possible in your most used gear, e.g. instead of 40/16 maybe 50/20 instead

cheers

[thelawnet]

8. Because the price of the socket and the price of the chain are similar.
9. And it therefore isn't worth the price of the chain to save the sprocket.
10. Especially when you've pushed both to their limits.

Depends on your wear rate, and ratio of chain price to cassette.

Decathlon prices:

chain/cassette
8-speed: £7/£15
10-speed: £13/£25
11-speed: £13/£35

If you get 3 chains @ 0.5% to 1 cassette, rather than 1 chain @ 1% to 1 cassette, then for the same (3%) cumulative chain wear the equation is

2 (3Cn + S) < 3 (Cn + Cs)

i.e.

Cs > 3Cn

So in that case the cassette needs to cost more than 3 times as much as the chain to justify changing the chain twice as often. This will rarely be the case, though there will be sometimes that it is true.

Of course if the chainrings wear out when wearing a chain to 1%, that will also affect the equation, and wearing to 0.75% rather than 0.5% is clearly not as dramatic as 0.5% vs 1%.

[horizon]

FWIW if you wait until a worn transmission actually slips it is probably costing you in terms of reduced efficiency, not to mention chainrings.

cheers

This got discussed in a previous thread about the downsides of letting the transmission degrade. Unfortunately I cannot find the thread but the impression I got was that there is an argument on an old bike for ignoring the wear and then replacing the transmission completely (or maybe never). The efficiency lost in popping to the shops isn't worth worrying about. I have enough of the engineer in me (not a lot ) to be a bit afronted by this but not much. If it doesn't seize up and doesn't slip, the bike might be at the tip before it becomes a real issue. There may be a safety issue (due to the slipping) but otherwise nothing to lose sleep over. But I am talking here about low mileage practical bikes, not Sunday best. Sorry, it's a bit heretical.

[Samuel D]

Various photographs were presented in this thread including a close-up by me and an example of extreme wear by rjb.

While wear can readily be seen on a sprocket, I don’t believe it’s practical to visually judge whether a new chain will skip on a given sprocket. You have to try it and see. That is not an onerous requirement because it’s not much quicker to replace a chain and cassette at the same time than to do so sequentially with a test ride in the middle.

[Brucey]

Various photographs were presented in this thread including a close-up by me and an example of extreme wear by rjb.

While wear can readily be seen on a sprocket, I don’t believe it’s practical to visually judge whether a new chain will skip on a given sprocket. You have to try it and see. That is not an onerous requirement because it’s not much quicker to replace a chain and cassette at the same time than to do so sequentially with a test ride in the middle.

To do the test you do end up cleaning a (potentially knackered) cassette though. This is almost a definition of 'how to waste your time' if in fact the cassette is too worn to carry on with. This is only eclipsed by the habit some folk have of cleaning a chain before measuring it; you might want to do this as a science experiment but in terms of practicalities it is just another time-waste.

BTW the cost of transmissions varies with the strategy; if you take 3 chains off a cassette at 0.5% and put them to one side, then do the same thing again with three more chains and another cassette, then wear them all 0.5% to 1%, then again 1% to 1.5%, you ought to expect the chainring(s) to be knackered at the end of it but you will have got 6 x 1.5% = 9% total chain wear out of the whole shooting match.

For 'ride to the shops' type bikes I think running derailleurs is basically uneconomic (vs a half decent IGH) unless the consumables are very cheap indeed; also the required gear range may be a lot less than on a full-blown touring bike; thus screw -on freewheels have some appeal, as does a single (pref steel) chainring. I've run a steel chainring on my IGH training bike for many tens of thousands of miles and it has eaten at least a dozen chains and a dozen sprockets in that time (I've lost count). There have been a couple of occasions where I have left the chain too long and a new chain has run rough on the (now worn) chainring for a few hundred miles, but other than that it has basically done what it says on the (cocoa) tin.

cheers

[mercalia]

not easy from inspection. the very small rings (11,12 etc) are from new "shaped" as if they are worn, unlike the middle rings when worn can look ok but still reject a new chain. rather its when to replace a chain? My test apart from measureing is to put pressure on the pedal and all is ok if there is no give or slop? even new chains and cassettes can slip. I had some campagnolo packeted SRAM chains very long time ago that when measured had zero stretch from new and were very fussy with cassettes - dont find that these days with chains I buy which are typically .25?