I know I should replace them if they "look like shark teeth", but I don't know what exactly what shark teeth look like. I know they don't exactly look new, but do they need to be replaced with my chain?
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3Doesn't look terrible to me. Do you have any chain skipping issues? I would not exchange anything if not. Some of the teeth have rams that may look as shark teeth, but you can see that they are aligned.– Vladimir F Героям славаCommented Jun 21, 2020 at 19:51
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1Vlad - thanks for your help. I have not had any skipping issues, just wanted to be safe (and reduce shipping costs if I needed to replace anything other than my chain)– Matt HCommented Jun 21, 2020 at 19:59
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1I see, I do not think there will be any issues with the new chain, but wait for the more experienced. The classical shark teeth look very different. But that is the final extreme stage of wear. You are surely not there yet. I cannot speak about any intermediate wear.– Vladimir F Героям славаCommented Jun 21, 2020 at 20:00
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1@Criggie: Looks very clean to me. Or has OP cleaned in the meantime and updated the pictures?– MichaelCommented Jun 22, 2020 at 8:47
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2My bike looks like that after one or two rides in fair weather, not to mention foul weather …– MichaelCommented Jun 22, 2020 at 10:42
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2 Answers
The idea is that chain force causes wear on the edge of the upcurve of the U-shaped gap between each gear tooth, eventually eroding the tooth profile so much that it becomes V or shark-tooth shaped in extreme cases (instead of flat-topped). The gear gap where the chain roller sits is then much wider than the roller itself, and the gear tooth is much narrower than the gap between rollers, so the chain can have slop and even slip on the gear, causing problems. Steel gears will normally wear more slowly than alloy gears, and chainrings (front) will normally wear more slowly than rear gears of the same material. The chain roller connections will also wear (this is called "stretch" but is just wear making the chain looser). Normally, chains get replaced more often than rear gear cassettes, which in turn get replaced more often than chainrings, but it will all vary with the materials and riding style involved.
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1That is true and repeated here very often, but is the cassette and the chainrings in the pictures worn? Commented Jun 21, 2020 at 20:03
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2In my opinion not much wear. I believe the leading upcurve in each rear gear gap is where the chain force is applied, while it is the trailing upcurve in each chainring gear gap that gets the chain force. Those upcurves look in good shape to me.– ArmandCommented Jun 21, 2020 at 20:14
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I bought a Dura-Ace chain ring thinking mine was worn. I was very surprised to find that the new one looked a lot like the used one. If you want to be sure ask a dealer to allow you to photograph a new large ring so you can compare them. Many modern gears are not cut in perfect arcs. This is to improve shifting performance not to increase durability. As far as the cassette is concerned it is difficult to say for sure as the picture is not face on. My opinion based on the images is that some wear shows but not enough to necessitate replacement now.
