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This is a follow-up to the question I need to replace a cassette for CS-HG500-10 but want to go XT

Yesterday I replaced the cassette, as well as the chain and the jockey wheels and went for a ride. The problem has not disappeared.

I'm thinking that the chainring is completely worn out, but I'm also starting to think about the tension of the chain.

I'm using the biggest chainring almost all of the time, and was in the bad habit of using it with the biggest sprocket of the cassette, cross-chaining the entire range. I've used this chainring about 7500 km (maybe 3/4 of that distance).

When I use the middle chainring (it has 3 chainrings at the pedal), the problem is pretty much gone.

Here is a YouTube video which I made today, where I'm fully breaking and then putting pressure on the pedal, you can see the chain jump.

Here are some photos of the chainring:

enter image description here enter image description here enter image description here

I have already ordered a replacement, but I wonder if chain tension could also be a factor with this.

Could this problem be removed by increasing the chain tension, or does it look like I generally should increase it after replacing the chainring? How could I do that?


Update: The new chainring arrived today. I took pictures of both and compared them. Here is the result:

enter image description here

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    Looks like a worn chainring to me. An easy way to check is to grasp the chain on the front of the ring and pull it forward. If you can pull it more than about half a tooth's depth then either the chain or ring is badly worn. – Daniel R Hicks Nov 28 '20 at 13:34
  • Worn out, but if the ring is worn out this badly, you better replace the chain and the cassette at the same time. – Carel Nov 28 '20 at 19:04
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    You say that you live in the big ring a lot. If you ride exclusively there, then perhaps a 1x chainring setup would suit you? That would put the only chainring in-line with your current middle chainring which will reduce the crosschaining effects. Will save you some weight (why carry a grannie you never use) On the downside, you'd loose 2/3 of your gear combos, and they're mostly on the lower end. Compromise with a chainring that is somewhere between your current big and middle tooth-counts, which will loose the highest gear or two. It is worth consideration. – Criggie Nov 28 '20 at 23:49
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    @Criggie The big ring exclusively was initially. I started biking about 1.5 years ago, but since around 0.5 years I've been climbing a lot more so I appreciate the small ring much more. I'm trying to avoid cross-chaining for a couple of months now, but I appreciate to have all the range available. A single ring would very likely not suite me. Thanks for your heads-up. The thing about the weight is that I don't care that much about it, as most of it is in my body. And I didn't care when my backpack grew to 3kg during the course of this year. I'm not at that point where weight would matter. – Daniel F Nov 29 '20 at 21:45
  • @Carel Yes I did replace them (there's a link to another question of mine in the post). I thought that those were enough, but it turned out not to be so. It's ok, I have a cheap replacement bike which I'm currently using and I'm now waiting for the new ring to arrive. – Daniel F Nov 29 '20 at 21:47
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I suspect the symptom of slipping could be mitigated for a while by increasing chain tension, but it would only be a short-term fix.

Development of OP's photo Flip of above photo
Here's a trace of one of your photos highlighting the teeth. See how the grannie ring has nice fat teeth, with a pronounced width and a curve over the top of each tooth? This ring has seen little use and is perfectly serviceable.

The middle ring is quite worn but probably worked well-enough with a worn chain (they tend to wear together. Notice the valley curves between teeth are not even - Compare with the flipped image on the right and they have a definite "handedness" - that is, in these photos the teeth on the middle ring are leaning "backward"

The big ring has developed short "flats" between the curve and the teeth. This is where your chain is slipping off because its too low.

ANSWER If you increase chain tension, it might help hold the chain's roller in the valley curve, but there's not enough metal left in the shoulders of the tooth to really make much difference.

The cost of replacement derailleur springs would be better spent on a new chainring.

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  • An extremely minor nitpick: the OP should be able to switch to the higher spring tension setting on his existing RD without buying a new spring, as shown in the Park Tools link I shared. I agree that this wouldn’t be worth the effort. – Weiwen Ng Nov 29 '20 at 15:02
  • Thanks! I'm already waiting for the big ring to arrive this week, but because of your answer I will also buy a new middle one and replace it sometime later (once they're in stock...). – Daniel F Nov 29 '20 at 21:51
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    Hi, due to the effort you have put into highlighting the teeth, and me having the new chainring available, I added an overlayed photoshop of new vs old to the question. Maybe it interests you. It looks like the smallest chainring has the teeth more defined, probably due to the small radius of the chainring and with it the need for a stronger "grip". – Daniel F Dec 1 '20 at 20:45
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I will focus on the chain tension part of the answer, as your big chainring is clearly worn out. However, do note that increasing the derailleur spring tension wouldn’t stop the chain skipping on the worn chainring. Therefore, this answer is mainly for the sake of interest.

By chain tension, I believe you actually mean the tension in the rear derailleur spring. This spring takes up slack in the chain. If your spring tension were too low, the chain could be slack in some or many gears. However, I don’t believe that it’s a setting most users need to manually change, as the factory tension is likely sufficient. From this Park Tools page on overhauling rear derailleurs, Shimano and Campagnolo RDs appear to have one setting for increasing the cage tension from the stock setting. SRAM appear to have one setting higher and one lower. I actually don’t know of any clear reasons you would want to increase the cage tension, but it is possible to do so. I suppose that if you were converting to 1x without a clutch equipped RD, you might consider increasing the cage tension, as discussed in this previous Q&A. (If you do this, you might consider using a chain guide as well.)

Less relevant to you, I recall that Friction Facts, an independent researcher later bought by Ceramicspeed, showed that all else equal, higher cage tension meant slightly more drivetrain friction, although manufacturers objected that the cage tension was necessary to ensure good shifting. I believe that Ceramicspeed’s oversized pulley cages contain at least one position which lowers the cage tension from the stock Shimano or Campagnolo setting. The amount of drivetrain friction at stake is quite small, likely considerably less than 1W.

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    “higher cage tension meant slightly more drivetrain friction” I’ve read tests where the big chainring (-> more tension) counter-intuitively had less losses. They theorized that it could be due to less vibrations. – Michael Nov 29 '20 at 12:08
  • @Michael that’s a different friction generating mechanism! The more the chain articulates, both laterally (I.e. cross-chained) as well as around the rings/cogs, the higher the friction. Smaller rings/cogs =more articulation. That is actually separate from the RD spring tension. – Weiwen Ng Nov 29 '20 at 15:00
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Chain tension is set by the springs in the derailleur. Some derailleur models have a tension adjustment in the upper B-pivot, but I think this is to adjust the range B-screw rather than change the overall force the derailleur puts on the chain.

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    For Shimano derailleurs, I think you can change the spring tension, but it involves removing the pulley cage and repositioning the cage spring. I’ve not done it personally, but I think there are three tension settings available. – Weiwen Ng Nov 28 '20 at 14:52
  • @Weiwen Ng On my M8000 XT derailleur, there are indeed two possible holes for the spring. – MaplePanda Nov 28 '20 at 18:09

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