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Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 9:57am
by Brucey
as posted in another thread, I wondered if this deserved a thread of its own.

I have a plan for a mad experiment; it is clearly possible to wear sprockets (a lot) by regularly changing chains whilst preserving the tooth profile well enough to run a new chain. Thus I have in mind a 'reverse-wearing procedure' for cassettes, which aims to resurrect sprockets that are already a little bit too worn to take a new chain.

It is predicated on the assumptions that,

a) at any stage, it is possible to fit and use a chain (without problems) that is ~0.2 or 0.3% less worn than the one that is currently fitted, and that
b) the sprockets will 'wear in' to the replacement chain fairly swiftly.

We've all done it; intended to change a chain a bit sooner than we actually did, and fitted a new one only to find that it skips on the worn sprockets. Occasionally I have 'fought the system' and run a new chain on slightly worn sprockets until everything beds in again. But it can take a while and there is always a risk of skipping under some load.

I've tried de-hooking sprockets (by grinding) and this is only a partial success; the problem being that once the sprocket is slightly hooked, the roller wants to sit in the hook, which is at a slightly larger PCD than with an unworn sprocket. As each tooth comes under load, the roller rides up a little ramp into the hook, and this affects how the other rollers sit in the sprocket too, such that even if the hook is removed, the chain may not feed cleanly onto the sprocket as it leaves the rear mech.

Image

shows the wear ramps very clearly, although this is an extreme example. To make a worn sprocket work OK with a new chain, I think it is necessary to remove the hook and the ramp.

My plan (such as it is) is to have several chains at my disposal, lets say 0.4%, 0.2% worn as well as new chains to hand.

Lets say I run a chain out to 0.7% and a new chain skips on the cassette. I would then run the 0.4% chain (which ought not skip) for a while ( a few hundred miles). Then I'd run the 0.2% chain for a while, and finally the new chain ought to run OK perhaps.... The idea is that at each stage the chain isn't liable to skip, but the worn sprockets are gradually recovering their shape such that they will tolerate a new(er) chain.

Has anyone tried this sort of approach...?

cheers

Re: Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 1:07pm
by rjb
I've only ever reversed sprockets to gain some extra life - uniglide ones. I have thought about filing hyper glide sprockets to allow reversal but not got there yet. BTW I have in the past recovered a worn chain which started slipping by using a tube and a hammer to tighten up the links. :roll:

Re: Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 1:30pm
by Mick F
It's the outer sprockets that wear the most for me, the ones with the smaller tooth count.
You can't reverse those, mind you, they only cost £3 or £4 each .............. providing they're Shimano.

Re: Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 1:59pm
by rjb
We'll have to get together Mick as we wear the middle sprockets on the tandem - the small sprockets are almost new. :lol:

Re: Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 2:01pm
by meic
Brucey wasnt talking about reversing the sprockets a-la-Uniglide but about bringing them back into use with a normal chain by wearing the already worn faces back into usable condition through using a succession of chains each less worn than the previous one.

I have played at matching worn chainrings and cassettes (on a tandem with 86bcd chainrings and tandem freewheel, neither of which are easily found/afforded) with worn chains in order to try and keep using them while minimising further wear but never imagined they could be improved in this way.

Re: Reverse-wearing a cassette...?

Posted: 24 Aug 2017, 4:06pm
by Brucey
meic wrote:Brucey wasnt talking about reversing the sprockets a-la-Uniglide but about bringing them back into use with a normal chain by wearing the already worn faces back into usable condition through using a succession of chains each less worn than the previous one....


indeedy. I have occasionally run a new chain with a cassette which contains one worn sprocket. After a while the skipping on that sprocket stops, presumably between the sprocket wearing and the chain enlongating, everything settles down.

However if my mad experiment works, there ought to be no skipping at any time during the 'reverse-wearing' procedure...

cheers

Re: Reverse-wearing a cassette...?

Posted: 27 Aug 2017, 8:55pm
by 531colin
This thread chimes with something that i have wondered about occasionally over the years.

Image

Image

Thats a cassette thats been on my winter bike since at least 2011, with a bit of card behind the most worn sprocket (in the middle somewhere)
I'm in the habit of using a chain wear gauge which I'm told measures the "wrong sort" of chain wear, and i'm so extravagant that i throw chains away before the gauge reckons they are worn out. With the price of 8 speed chains, I can't be bothered to clean the things, but i reckon that i spend 10 times as much** on posh coffee than I do on chains. Never more than 2 chains a winter, and "summer bike" chains go on for a couple of summers, with no road salt.
A new chain has never skipped on that cassette (or on any other cassette that I have used like this).....but there is a lot of "wear" on the teeth. (on some sprockets)
So my question is......is that the "right sort" of wear?......
Because the cassette has never been run with a worn-out chain, is the tooth profile "right" despite the wear?....will my cassettes work until I wear the teeth right off?

**.....much more than 10 times, actually

Re: Reverse-wearing a cassette...?

Posted: 27 Aug 2017, 10:10pm
by Brucey
531colin wrote:This thread chimes with something that i have wondered about occasionally over the years.

A new chain has never skipped on that cassette (or on any other cassette that I have used like this).....but there is a lot of "wear" on the teeth. (on some sprockets)
So my question is......is that the "right sort" of wear?......


I think if it isn't, I can't tell...

...Because the cassette has never been run with a worn-out chain, is the tooth profile "right" despite the wear?....will my cassettes work until I wear the teeth right off?


yes I think so on both counts.

Another way of putting my idea is, if you took a 0.7% worn chain off a cassette, and used a 0.4% worn chain on it, I'd say you have a fair chance that it won't skip (even if a new chain might) and that after a period of use the sprocket wear would look like the wear on any other cassette that had been used with a 0.4% worn chain, e.g. like the wear above.

There is quite a lot of metal missing from the sprocket above but the tooth profile (on the loaded face of each tooth) still looks OK to me. I have offered new sprockets up behind 'worn' ones like that (that have never seen a very worn chain) and the tooth profiles look almost identical if aligned correctly.

By contrast teeth that have seen a more worn chain than that are no longer almost identical; they typically have a ramp at the base and a hook. Once the worn chain is a bit worse than is enough to cause a hook, the top of each tooth quickly gets spifflicated. To recover the tooth profile then becomes very difficult; lots of material needs to be removed from the tooth to get the right shape back again.

cheers

Re: Reverse-wearing a cassette...?

Posted: 28 Aug 2017, 7:19am
by 531colin
Interesting......
My summer bike has a 9 speed cassette made up from 2 cassettes (so i get intermediate ratios I'm happy with)
....so i could try your test of lining up the loaded faces of a worn sprocket and a similar new sprocket.
Theres probably less wear on the summer cassette, due to the absence of road salt.

Re: Reverse-wearing a cassette...?

Posted: 29 Aug 2017, 6:03pm
by Zanda
An interesting experiment and I await the results, perhaps after Brucey has ridden 800 miles.

Incidentally, I rarely dispose of part-worn chains and now have a few of them, some single speed, some 6 speed, some 8 speed. The best way to store them is empty VHS cassette boxes, one chain per box. They're made of quite tough plastic and have a built in 'label window' on which you can write the width, length and wear. The label stays clean even when the box is handled with oily hands.

Re: Reverse-wearing a cassette...?

Posted: 29 Aug 2017, 7:56pm
by MikeF
531colin wrote:Thats a cassette thats been on my winter bike since at least 2011,
Any idea of the mileage?

I too wonder whether cleaning 8 speed chains is worth the hassle and expense of cleaning. As you note they don't cost much. I put on a new chain 1500 miles ago and at first it started slipping slightly on the 28 tooth sprocket (next largest). After a little mileage it seemed to "bed" down. According to my Park chain gauge I can't detect significant chain wear at the moment.

I've looked at the cassette, which has now been 8500 miles, and the sprockets don't look particularly worn or hooked, but maybe I need to look closer.

Re: Reverse-wearing a cassette...?

Posted: 29 Aug 2017, 9:37pm
by 531colin
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....

Image

and superimposed...

Image

Image

Now, thats got to be a bigger mileage, but much less "wear" with no road salt.

Re: Reverse-wearing a cassette...?

Posted: 29 Aug 2017, 10:15pm
by mig
why has there never been a cassette made of carbon?

Re: Reverse-wearing a cassette...?

Posted: 30 Aug 2017, 10:55am
by Brucey
probably the same reason as CF chainrings are not popular, but CF sprockets will be worse; after all aluminium chainrings are 'normal', but aluminium sprockets have a very short life expectancy.

It has been tried

Image

https://www.bikerumor.com/2012/01/31/found-63g-carbon-fiber-cassette-from-experimental-prototype-and-more/

but presumably the results were not encouraging enough for others to follow suit.

cheers

Re: Reverse-wearing a cassette...?

Posted: 30 Aug 2017, 12:49pm
by mig
:D

i would have thought that a pro rider would have tried one in an uphill TT by now but maybe they are that bad..! or maybe there hasn't been such a test.

it's not possible to have a screw thread in carbon i assume looking at the small sprockets there.

re. tooth wear. i did once wear out a 1/8th fixed sprocket. the quality was so poor that the teeth had started to twist along their length resulting in a strange trnasmission to say the least!