Is my chainring worn?

[toby123]

Hi, in a few weeks I'll be replacing my chain and cassette and I'm just wondering whether I should replace the outer chainring at the same time. The question is, is it worn to the extent that if I continue with it, I'll be losing efficiency in the drivetrain? I think I need to have a good look around at new ones in bike shops but I'd really appreciate if anyone can offer their opinion based on these photos.

I've noticed that the teeth on the outer ring are much more spiked than the ones on the inner, which I must use for no more than 10% of the time. Is this due to wear or are they cut differently in the factory? In future, I'll have to pay much more attention from the beginning...

My other question is whether I need to worry about compatibility with Campag, or is it just a question of which chain I use (currently KMC)?

 

[Nibor]

they are fine hardley worn at all

 

[User6179]

+1 they are fine

 

[Globalti]

I disagree, the outer ring looks half worn to me. I'd consider replacing it when I changed the chain and cassette. What does @Yellow Saddle think?

 

[Yellow Saddle]

He says the photos are inconclusive but he can see that the OP is a big blade grinder and hardly ever uses the small ring an that the big ring is somewhat worn. Chainrings, unlike cassettes, don't wear evenly but they wear in two spots corresponding to the power strokes of the left and right leg. These strokes have small arcs from the ten-past position 20-past position if you consider the left and right cranks to be minute arms on a clock. The sections of chainring that take strain during these two power pulses are opposite each other on the clockface and with the right crank horizontal forward, would be between the ten-to and ten-past position on the clockface and diagonally opposite side which will be twenty past to twenty to (still with the right crank pointing forward and looking from the right side). The difference between tooth (cog) wear in this position and dead-on top and bottom is also an indication of how perfect your stroke is executed.

Post a photo of the chainring dead face-on or of those two regions and we'll see. Big chainrings wear slower than small ones for obvious reasons but even with lots of wear, the system tolerates it and chainsuck doesn't occur on large chainrings because the cosine error is smaller. This refers to the length of the pendulum if you consider the radius of the chainring to be the length of the pendulum. On smaller chainrings the tooth makes a more pronounced hook as it moves out of the chain. You can demonstrate this by making a C with your fingers, clenching your elbow against your side and swinging your fist in an arc. Now do the same with your arm extended and notice how the hook formed by the C has more bite in the small arc than the long one.

That was a bit long-winded but abbreviation is not his thing.

 

[Apollonius]

Not too sure what your worry is regarding Campagnolo. Your FSA chainset is standard issue on many Bianchis, and works fine with Campagnolo. A chain is a chain, and KMC are very good.

 

[accountantpete]

I have a lightly used example of the same chain ring (earlier model) in my drawer.

The U's are a bit neater but personally I'd be happy to use your ring if I had a cheapish chain and cassette on.

 

[Apollonius]

That picture shows what an odd profile the FSA chainrings have. They look knackered when new.

 

[toby123]

That picture shows what an odd profile the FSA chainrings have. They look knackered when new.

Why's that then?

 

[Nibor]

He says the photos are inconclusive but he can see that the OP is a big blade grinder and hardly ever uses the small ring an that the big ring is somewhat worn. Chainrings, unlike cassettes, don't wear evenly but they wear in two spots corresponding to the power strokes of the left and right leg. These strokes have small arcs from the ten-past position 20-past position if you consider the left and right cranks to be minute arms on a clock. The sections of chainring that take strain during these two power pulses are opposite each other on the clockface and with the right crank horizontal forward, would be between the ten-to and ten-past position on the clockface and diagonally opposite side which will be twenty past to twenty to (still with the right crank pointing forward and looking from the right side). The difference between tooth (cog) wear in this position and dead-on top and bottom is also an indication of how perfect your stroke is executed.

Post a photo of the chainring dead face-on or of those two regions and we'll see. Big chainrings wear slower than small ones for obvious reasons but even with lots of wear, the system tolerates it and chainsuck doesn't occur on large chainrings because the cosine error is smaller. This refers to the length of the pendulum if you consider the radius of the chainring to be the length of the pendulum. On smaller chainrings the tooth makes a more pronounced hook as it moves out of the chain. You can demonstrate this by making a C with your fingers, clenching your elbow against your side and swinging your fist in an arc. Now do the same with your arm extended and notice how the hook formed by the C has more bite in the small arc than the long one.

That was a bit long-winded but abbreviation is not his thing.

This being the case could he not rotate the cahinring to reposition the worn sections and extend its usable life?

 

[Yellow Saddle]

This being the case could he not rotate the cahinring to reposition the worn sections and extend its usable life?

Yes and no. Chainrings intended to be used as the big (right hand side) chainring have a little stop built in to prevent the chain from dropping into the wedge formed by the crank and spider. If a chain falls in here under power, it is stuck forever. If you rotate the chainring two things happen. This little stop moves on a couple of degrees and no longer protects the crank. Secondly, the shifting teeth on both chainrings, those ones that are shorter than the others, are positioned vis a vie each other to facilitate the shift. If they go out of sync shifting becomes poor.

Having said that, in the old days there were no shifting teeth and we still shifted normally and you could rotate the chainring. We live in a world of built-in obsolescence. It must be remembered though that one a tooth is worn to a shark fin shape, it no longer meshes with the chain and will hit the incoming roller before sliding past it. This is not good and causes a noisy twanging noise in the tight chain.