Reverse-wearing a cassette...?

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MikeF
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Re: Reverse-wearing a cassette...?

Postby MikeF » 31 Aug 2017, 10:27am

531colin wrote:
MikeF wrote:
531colin wrote:Thats a cassette thats been on my winter bike since at least 2011,
Any idea of the mileage?..........


Not much better than a guess.....
I doubt I do 100 miles a week all winter, but its an easy number....if i ride the winter bike 25 weeks a year, for 6 winters thats 15,000 miles...
if i only do 70 miles a week, its 10,500 miles.
I'm generally out for 2 "day" rides and one social coffee ride a week, so i think 70 miles a week is a low estimate.

Heres the corresponding summer bike cassette, again since 2011...compared to an un-used 8 speed sprocket the same tooth count, but black....

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and superimposed...

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Now, thats got to be a bigger mileage, but much less "wear" with no road salt.
That looks like very little wear to me, but I'm not an expert.
"It takes a genius to spot the obvious" - my old physics master

Brucey
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Re: Reverse-wearing a cassette...?

Postby Brucey » 31 Aug 2017, 1:35pm

I think there is about 0.5mm missing from the loaded face of the tooth, and that if it were 'missing in the wrong way' the sprocket wouldn't take a new chain. As it is, it is worn in such a way that it almost certainly will.

You will note that the top of some of the worn teeth are showing a slight burr; the 'tooth top spifflication' I mentioned is like this, but much much worse.

cheers
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531colin
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Re: Reverse-wearing a cassette...?

Postby 531colin » 26 Aug 2018, 2:50pm

Here we are, another year older...….
While giving my winter bike its annual (summer) sort-out, I noticed that the 8 speed cassettes are of a sufficiently old design that they are fixed together by 3 tiny Allen head screws; so I have been able to take apart the old cassette and a new one, and superimpose the teeth of the 21t sprocket. This is the sprocket that shows the most wear; I guess from another discussion (here somewhere?) that sprocket gets used for some combination of hard pedalling and a lot of time. (I can't believe that I use a sprocket that big for more of the time than smaller sprockets; but its one I would use on a rising road when I'm pedalling harder than on the flat.)
https://www.flickr.com/photos/52358536@N06/43372383615/sizes/h/
https://www.flickr.com/photos/52358536@N06/43372383635/sizes/h/
https://www.flickr.com/photos/52358536@N06/43372383595/sizes/h/
That cassette had at least one new chain last winter, without skipping.
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Marcus Aurelius
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Re: Reverse-wearing a cassette...?

Postby Marcus Aurelius » 26 Aug 2018, 4:35pm

You can’t teach an old cog new links. What you propose to do is going to take its toll on a chain, to the point it would make it not worth the bother.

Brucey
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Re: Reverse-wearing a cassette...?

Postby Brucey » 26 Aug 2018, 7:13pm

Marcus Aurelius wrote:You can’t teach an old cog new links. What you propose to do is going to take its toll on a chain, to the point it would make it not worth the bother.


I have run multiple chains in succession on a single cassette in the past, and so have lots of other folk; Colin for example. Normally you can do this if you change chains when the old one is worn to 0.5 or 0.75% , but the exact value seems to vary with the rider, the measuring technique and for all I know the chain/casssette type used too.
I have not observed myself or heard anyone mention that (say) the second, third and fourth chains lasted a lot less long than the first one did, despite the fact that they (unlike the firstone ) were fitted onto a cassette that was already worn.

My point is that the difference between skipping under load and not can be of the order of a few microns difference in wear on the sprocket. I am pretty sure that (say) a 0.5% worn chain will not skip on a 1% worn sprocket, and after a short period of use the sprockets will (where it matters) most closely resemble those which have only ever been used with a 0.5% worn chain. At this point it ought to be possible to fit a new chain and for it to run without skipping.

FWIW if you use a slightly worn chain on unworn sprockets, it doesn't skip, but it is usually rather noisy. I think this noise arises because as the chain unwraps from the sprocket, the load is abruptly transferred from one tooth to another, and each roller must move equally abruptly in order to assume a position on each tooth in which it is able to transfer the load properly. This I can believe wears both the chain and the sprocket at a higher rate than normal.

However using a slightly less worn chain on slightly more worn sprockets is usually quiet-running, at least up to the point that the wear mismatch is sufficient to cause skipping under load. I would conclude from this that the wear rate is likely less, also.

If cassettes were cheap and easy to source and chains expensive and difficult to obtain, one would be trying to maximise the life of the chain, not the cassette. But it isn't like that; chains are cheap and fairly ubiquitous; you can use almost any make, and n+1 or even n+2 chain (and even n-1 sometimes) will normally work well enough on an 'n' speed system if you can't get anything else. This means that if you wanted to fit a new chain (that would work OK ) to any bike you might need a minimum of three different chains.

By contrast cassettes are rather more specific in nature and can be very expensive too; you can't use n +/- 1 unless you have a friction shifting mode and between the variations in fitting and ratios, there are literally hundreds of different cassettes that vary in price from cheapish to 'ridiculous' in price; prolonging the life of the cassette seems like a good idea all round.

cheers
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531colin
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Re: Reverse-wearing a cassette...?

Postby 531colin » 26 Aug 2018, 7:48pm

Brucey wrote:...........
I have not observed myself or heard anyone mention that (say) the second, third and fourth chains lasted a lot less long than the first one did, despite the fact that they (unlike the first one ) were fitted onto a cassette that was already worn............

Well, I don't keep records of any sort, but the cassette I photographed came into service no later than 2011; so its been used for six winters, so at a guess 9 chains?
All I'm doing is throwing away my chains before they have the opportunity to wreck the sprockets, and I've been doing it for around 20 years; the last set of sprockets I had a new chain skip on were on a Sachs Aris screw-on freewheel.
I find Brucey's idea of reverse-wearing sprockets interesting as a concept, but I'm much too lazy to deliberately set aside a chain at a particular wear state so that I can put some damaging wear on a cassette and then attempt to re-habilitate the cassette.....much easier to avoid damaging the cassette in the first place!

Samuel D
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Re: Reverse-wearing a cassette...?

Postby Samuel D » 10 Oct 2018, 1:40pm

I found this interesting discussion with a search and thought I would add something.

(Click on the photographs to see bigger versions.)

Image

On the right is a new CS-HG50-8 cassette with 13-, 14-, 15-, 17-, 19-, 21-, 23-, and 26-tooth sprockets. I really like this cassette and fear the day Shimano stops making it.

On the left is an identical cassette, even bought simultaneously I think, with ~16,000 km on it. I always replaced the chain as soon as 12 inches became 12 and 1/16th as measured with a ruler.

I did this five times (i.e. six chains) and was starting to think that under this regime the cassette might last until the teeth wore to narrow spikes and broke off. However, on the sixth new chain, it skipped on the 15T and 19T sprockets. The 19T sorted itself out after 100 km but the 15T did not, so I retired the cassette.

To eliminate any confusion caused by Shimano’s shaped teeth, here’s two identical teeth from the 19T sprockets side by side with an index card behind them. (This is shortly after the 19T started working again, although I suppose it’s the chain as much as the sprocket that changed.)

Image

Five chains is fewer than 531colin’s nine. Is that because Colin uses a pessimistic chain-wear gauge while I use a ruler?

Brucey
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Re: Reverse-wearing a cassette...?

Postby Brucey » 10 Oct 2018, 6:32pm

new chains come between 0.0% and 0.2% over length. I think that if you usually have the latter and then get the former, the 'ramp shape' will encourage skipping.

FWIW when the new chain hits 0.2 or 0.25% , I bet it will run OK on the old sprockets. This will then give you a chance to reverse wear the sprockets; if you run the chain to 0.3% on the old sprockets and then fit another new one, I reckon it mightn't skip.

cheers
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531colin
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Re: Reverse-wearing a cassette...?

Postby 531colin » 12 Oct 2018, 12:12pm

Samuel D wrote:……….
Five chains is fewer than 531colin’s nine. Is that because Colin uses a pessimistic chain-wear gauge while I use a ruler?


My "5 chains" is little more than a guess, I don't keep records.
I not only use a gauge which includes the "wrong sort" of wear, I also throw away chains which are rusty or otherwise manky even if the gauge shows them to be "within limits". 8 speed chains are so cheap that I can't be bothered to mess about cleaning them....on the other hand, I have chainrings which are old enough to vote, and yet are still running OK.

rjb
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Re: Reverse-wearing a cassette...?

Postby rjb » 11 Nov 2018, 3:09pm

i have just replaced the 8 speed cassette, chain, and chainset on the tandem. Its now done 42,000 miles. I have to admit maintenance was laxed as i was too busy riding the bike. My maintenance regime is normally 2 chains rotated every 2000 miles and then replace the cassette and chains at 8000 miles. This was due last year in the summer. As the chainset was original and also showing signs of needing replacement i decided to run it too destruction over the winter. i let it run on for a further 8000 miles on the same chain before the cassette starting slipping occasionally but not to the point of being unridable. Dont forget this is a tandem with 2 people contributing to the load. I only had a part worn sprocket for comparison but you can see what wear has occured over approx 15000 miles. This may even be an underestimation as my records got lost in a usb stick failure. Its only the middle sprockets which exhibit this wear. I built up the replacement cassette using the top 2 small sprockets and the bottom sprocket which showed negligable wear. The 2nd chain which has been on for the last 8000 miles is stretched but only just to an 1/8" over 12".
Shows how far you can push the envelope. :mrgreen:

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At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

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531colin
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Re: Reverse-wearing a cassette...?

Postby 531colin » 11 Nov 2018, 5:41pm

That's definitely the "wrong sort" of wear, if you want to run a new chain!

Samuel D
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Re: Reverse-wearing a cassette...?

Postby Samuel D » 12 Nov 2018, 9:21am

I’m surprised even a terribly elongated chain didn’t skip on those vestigial teeth.

Brucey
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Re: Reverse-wearing a cassette...?

Postby Brucey » 12 Nov 2018, 9:52am

me too...

cheers
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531colin
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Re: Reverse-wearing a cassette...?

Postby 531colin » 15 May 2019, 9:35pm

Another year has gone , and here is my annual photo of my 8 speed "winter" cassette.
This photo just taken with card behind the most worn sprocket. Cassette has been in use since at least 2011 and has had a new chain this last winter without skipping. or maybe 2 new chains, I can't remember.
Compared to a new cassette, the teeth have worn really thin, but theres no skipping so I guess I'll try it for another winter. It looks to me that there is a danger of the teeth bending , and that would change their profile!
https://www.flickr.com/photos/52358536@N06/32913842707/in/album-72157624571269648/
https://www.flickr.com/photos/52358536@N06/33980730148/in/album-72157624571269648/
I think a lot of the "wear" is corrosion from road salt; the plating has taken a pasting!

NickJP
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Re: Reverse-wearing a cassette...?

Postby NickJP » 16 May 2019, 7:27am

Rohloff sprockets are reversible - when the teeth start to get hooked, you can remove the sprocket, flip it around, and with a new chain you've effectively got a new sprocket.