Does this chainring need to be replaced?

Question

Here is a closeup of my triple:

All three rings are Shimano Ultegra and have never been changed. They probably have at least 12000+ km on them. I've been pretty good about changing the chain regularly although at this point I'm pretty sure that the rear cassette is in need of changing.

If you compare the middle ring with the two outer ones, it looks fairly worn (shark fin pattern). Is it bad enough to need replacing? If I just change the chain and rear cassette will I be entering a world of pain?

UPDATE: Thanks for the advice so far. I have a new cassette and chain standing by but would need to order a new middle ring since it's a bit exotic (one LBS didn't know Shimano still made Ultegra triples). I know that there's a lot of km's on these rings (mostly on the middle one) and I'm also familiar with the "if it still skips, try changing it" philosophy, but I was hoping for a more objective answer. Something about the wear pattern or what to look for if I put a new chain on?

Answer 1

Judging by Sheldon's Guide, it definitely looks like you are in need of a new chainring. Your middle and larger sprockets in particular look like they have taken on a significant ramp-like profile, which will surely lead to lackluster shifting.

Answer 2

Presumably with 12K+ km, and never having bought new chain rings, you have a very high cadence. You should get a new chain every time you change your cassette, btw.

If you are doing the work yourself, I don't see any reason to change the chain ring immediately. Try the new cassette and chain and see how it works. If it isn't broke, don't fix it. If it doesn't ride well after changing the first set of parts then yes, change it.

On the other hand, if you are taking it to a shop and paying for the work, it's probably worth having them put on a new chain ring while they've got it in the stand. A good shop will test ride it and be able to tell you if it is needed before you buy.

12K is a lot of distance for the equipment, so I wouldn't hesitate to change it either way.

Answer 3

I would only replace if:

1. The chain is skipping because of wear of the teeth
2. You get chainsuck even when the chain is clean (small chainrings are more prone to chainsuck)

For cassettes I would not consider changing unless it skips when you have put on a new chain.

The best tactic is to change your chain often enough so that you minimise the wear in your cassette and chainrings.

Answer 4

I use to successfully reshape chainrings like these using a round file (diameter more or less similar to the chain roller). This is a tried and tested method, and is very easy (much more than doing the same with the cogs, which I also do when needed). The only limitation is with skill and time, since it is a bit monotonous and require a bit of labor.

You just have to remove material in a way that it gets the same shape as the others, which means the teeth would be thinner looking from the side. Of course, it is necessary to remove the chainring from the crankset.

(and a final advice would be: change the chain often, before this happens again)

The picture below shows the regions that must be removed:

( I am attempting to edit this reply as I'm afraid it's incorrect ...the red areas shown should not be removed ....if any "dressing" of the chainrings is required it will be on the other side of the teeth. The photo was obviously taken from the non-drive (left) side of the bike so the granny ring is nearest. The photo incorrectly indicates removing material from the right side of the teeth (where very little to no wear occurs). The area the chain contacts in this photo is on the left side of the teeth and this is where the chain loading, and therefore, wear occurs. ..eventually creating a hooked profile which can be filed away to avoid chain suck. I hope that helps clear up any confusion !)

Answer 5

Interestingly enough, I just replaced my middle ring on almost the identical equipment that you have. It cost me $27 US dollars for a new 42-tooth Ultegra ring (from Amazon), and it took about 5 minutes to swap out. The shifting wasn't the problem; it was the horrendous "snap" I would get when pedaling more than idly when sitting on the 42... and mine isn't nearly as worn as yours!

(A few facts about chain-line wear:

1. The actual wear-out of almost any chain is the rollers against the pins. The rollers are just a little cylinder of metal, and it isn't as hard as the metal of the chain pins, so it wears first. As the roller gets thinner-walled, the effective length of the chain gets longer, although measuring pin-to-pin with a ruler barely changes at all!
   
2. Old chain/worn rings "works" because the chain has so much slop in it that it can get right over the teeth.
   
3. New chain/worn rings fails in this way: Picture the top of the chainring, just as the chain is feeding onto it. A link goes over a pin, and the roller "beds down" into the hollow of the shark-tooth pattern. The next roller would do the same, but first it has to clear the tip of the next tooth, which it can't quite do under high tension, so it "sits on". As the chainring rotates, eventually the roller that it stuck on the tip of the tooth "drops in" - with a loud snap and a very disconcerting feeling of the pedal dropping out from under your foot. Ride it that way for very long and you'll wear out the chain VERY QUICKLY INDEED
   
4. Filing out the teeth of a worn ring to keep using it - yeah that oughta work, in a way, but the shifting performance won't be as nice. The reason the teeth are so strangely shaped is for smoother, quicker shifting. Also the teeth will be much weaker and the end-game of filing them down for "extended" life is that they will eventually start breaking under high load.)

Answer 6

In general, you only need to replace the front rings when they give you problems, either with skipping, chain suck, or shifting problems. Running with a worn front will not add appreciably to the wear of other components.

But a well-equipped bike shop should have a gauge for checking the rings.

Answer 7

If it works (so it successfully engages to and disengages from a chain), not even close to needing replacement based on the tooth shape.

I've ridden chainrings with far more shark-edged teeth. They work just fine.

There are three reasons you might want to change a chainring due to teeth problems:

• It doesn't engage to a chain anymore or the chain is slipping (very rare).
• There's so little teeth remaining that you're genuinely worried about bending the teeth if great force is applied to the chainring. This doesn't apply to your ring, there's a lot of teeth remaining on that one.
• You get chainsuck, i.e. the chainring engages to the chain but fails to disengage. This is more common on small MTB rings with long cage rear derailleurs than on large road rings with short cage rear derailleurs.

Additionally, if you shift a lot, the shifting aids could theoretically wear. That's not fatal, people have been riding chainrings with no shifting aids on a front derailleur bike for 50+ years no problem. I wouldn't change a chainring due to degraded shifting but just accept the degraded shifting as a fact of life. Saves a lot of money that way.