Cycling UK Forum

What does the audience feel about the state of the middle ring in this chainset?

It worked fine with the previous chain, but that had worn excessively and required a new cassette - both of which I’ve just fitted.

The chainset is from the late 90s. Mileage not logged as bike mainly used as local errands/shopping bike.

Due replacement - not too expensive from Spa Cycles (as an example)

I would say if the chainring works, it works.
Unless you are fussy about transmission rumbling on a shopping bike?
It’s a long time since I saw an STX (RC?) chainset; is that a removable/replaceable spider?

Interestingly, that is exactly what I was thinking. Going to go there during the week for some other bits and thought I’d pick up a new ring.

531colin wrote: ↑10 Nov 2024, 3:52pm I would say if the chainring works, it works.
Unless you are fussy about transmission rumbling on a shopping bike?
It’s a long time since I saw an STX (RC?) chainset; is that a removable/replaceable spider?

Yes, I undid the 4 bolts on each side to check that they weren’t seized. All came apart.

Bike is from 1998.

You can't necessarily tell by the appearance. I too recently replaced my cassette, very worn chain, and large chain ring. The small chain ring didn't look bad, so I kept it. However, as soon as I used it on a steep hill it began jumping like anything, eventually throwing off the chain. I replaced the chain ring and all is fine.

I very much like STX-RC, but outer and middle rings shot. RC can be nominal 7 or 8 speed I think. Just about any rings of correct BCD will be fine.

I probably carry on using my chainrings when other folk would have given up on them, so maybe I am not the right person to offer advice, but I more or less agree with Colin; if it works at all, that is probably good enough. Also, they are usually not difficult to deal with, unlike sprockets. The kind of tooth wear that, in a sprocket, leads to skipping, is more likely just to cause a noise or a vibration instead in a chainring. The chain always engages when it is loaded, unlike what happens with a sprocket. The following types of wear and means of dealing with it are known and understood;

1) normal wear arising from a worn chain. A worn chain always has a pitch that is slightly longer and this nearly always causes the chain to start 'climbing' the teeth under load. That is, the chain tends to sit a wee bit further out, where the pitch of the teeth is a better match for the slightly worn chain. The most loaded chainring teeth (ie. those which see the chain tension directly during the power stroke) tend to wear first, typically leaving the teeth nearest the RH crank and those opposite the LH crank virtually unworn. Provided there are at least some vaguely unworn teeth left, the chain is unlikely to slip wholesale. This can occur of course, but it typically only ever happens if the chainring is severely worn, with all the teeth shorter than normal.

2) wear that produces hook-shaped teeth. It is important to realise that, in a derailleur system, both the chainrings and sprockets may be manufactured with a pitch that is fractionally undersize. This means that even if a 'perfect' chain (ie. one in which the pitch measures exactly 12.700 mm over several links) on unworn chainrings, the load is unlikely to be shared over many teeth. This can often be seen in an unworn transmission, where even a loaded chain can be mysteriously slack on the chainring after the first few teeth. Needless to say, if everything were manufactured with an exact and uniform pitch, this wouldn't happen in the same way. A side effect of this is that even a very sightly worn chainring may 'grumble' with a new chain whereas this would be less likely if the pitches were a more exact match.

3) Wear that causes 'chainsuck'. This falls into two main categories; 1) conditions that make the teeth fatter, and 2) conditions that allowed hooked teeth to 'hang onto' the chain. 1) includes dirt as well as chainrings that are just too soft, so they yield too easily.when loaded and 2) includes many of the geometry tweaks normally required for offroad use, such as increased roller clearance or changes to the amount of underizing.

Note that whenever very small chainrings are used, there is a danger that chain tensions become too high, which is probably why some manufacturers seem to have come unstuck, using chainring materials which are just not strong enough for small chainrings.

fastpedaller wrote: ↑10 Nov 2024, 3:36pm Due replacement - not too expensive from Spa Cycles (as an example)

Once I had a look at the photos that’s what I thought too. It seems that the chainset has done many years of service and so long as the OP is comfortable with the costs then why try to squeeze more service out of it instead of replacing worn parts now? I’m a life long tightwad but even I recognise that there’s a time to accept that you’ve had your ‘money’s worth’ and a need to buy new (when you can).

Perspective is a wonderful thing. Though I don’t do many miles in it I run a small old car too; a casual estimate of its running costs comes in well over a grand a year. A well cared for bike can do several thousand miles a year - maybe near to or even more than what you drive - and (compared to a car) cost relatively little to run; without being profligate invest in your bike and don’t begrudge the cost.

Edit. I note that the chainrings are secured on four ‘bolts’, as such it should be possible to rotate them through 90 degrees to place the less worn teeth where the more worn teeth now are (ie. the place of highest loading between chain and ring). The OP might extract more life that way but if he can both afford and get replacement parts then I think that a better way to go.

The wear looks acceptable to me, I usually retire a chainring when the tips of the teeth get pointy. BUT I would be very concerned about the tooth with a chunk missing, so I would replace on that basis. It looks like it could bend or snap.

I have included a pic showing two chainrings which I think are too worn. The top one has a sharks teeth profile on some teeth. I find when it gets to this stage the wear rate accelerates dramatically.

Cyclewala wrote: ↑10 Nov 2024, 3:24pm What does the audience feel about the state of the middle ring in this chainset?

after 25+years, i think its time to shift to the small ring.

bluespeeder wrote: ↑13 Nov 2024, 9:33am BUT I would be very concerned about the tooth with a chunk missing, so I would replace on that basis. It looks like it could bend or snap....

it is perhaps worth noting that shimano appear to save their heaviest manipulations for steel middle chainrings, so they often look worn out or broken, even when they are new. I'm not sure which tooth has 'a chunk missing'; however I do note that when a new chain is fitted, owing to the pitch mismatch, the most worn teeth conveniently see the least load.

Brucey wrote: ↑13 Nov 2024, 5:18pm

bluespeeder wrote: ↑13 Nov 2024, 9:33am BUT I would be very concerned about the tooth with a chunk missing, so I would replace on that basis. It looks like it could bend or snap....

it is perhaps worth noting that shimano appear to save their heaviest manipulations for steel middle chainrings, so they often look worn out or broken, even when they are new. I'm not sure which tooth has 'a chunk missing'; however I do note that when a new chain is fitted, owing to the pitch mismatch, the most worn teeth conveniently see the least load.

The last pic at about 7 o'clock. It looks like there is a ramp pin there as well so there cannot be a lot of aluminium holding this in place.

bluespeeder wrote: ↑14 Nov 2024, 9:12am

Brucey wrote: ↑13 Nov 2024, 5:18pm

bluespeeder wrote: ↑13 Nov 2024, 9:33am BUT I would be very concerned about the tooth with a chunk missing, so I would replace on that basis. It looks like it could bend or snap....

it is perhaps worth noting that shimano appear to save their heaviest manipulations for steel middle chainrings, so they often look worn out or broken, even when they are new. I'm not sure which tooth has 'a chunk missing'; however I do note that when a new chain is fitted, owing to the pitch mismatch, the most worn teeth conveniently see the least load.

The last pic at about 7 o'clock. It looks like there is a ramp pin there as well so there cannot be a lot of aluminium holding this in place.

531colin nailed it with if it works, it works. You can lose a tooth on a chainring and more often than not it'll continue working and shifting fine. That said the tooth profile on the middle ring looks like chain-suck is around the corner so I'd either replace it soon or get the metal file out.

bluespeeder wrote: ↑13 Nov 2024, 9:33am The wear looks acceptable to me, I usually retire a chainring when the tips of the teeth get pointy. BUT I would be very concerned about the tooth with a chunk missing, so I would replace on that basis. It looks like it could bend or snap.

I have included a pic showing two chainrings which I think are too worn. The top one has a sharks teeth profile on some teeth. I find when it gets to this stage the wear rate accelerates dramatically.

download/file.php?id=116964&mode=view .....sorry, too stupid to be able to put "bluespeeder's picture here!

To be fair, that pattern of "wear" is caused by using a worn chain. (The natural history is this; the chain wears where the inner link plates pivot on the rivets, this wear means the rollers are further apart so the rollers ride up the teeth where the gap between teeth matches the (new) roller separation, and the teeth eventually wear to a point.)

IMG_5475 by 531colin, on Flickr

Above is the wear pattern you (eventually) get if you replace the chains before they get so worn that they modify the tooth profile.
On the top (worn) ring the teeth are worn at the bottom of the loaded face, its actually easier to feel than to see if you have the ring in your hand. This can eventually lead to "chain suck" where the chain fails to disengage from the chainring at the bottom. ...fairly easily corrected by using a file to restore the original tooth profile. (from here....viewtopic.php?t=116834&hilit=reverse+we ... e&start=30