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I need some help understanding how to solve the issue of chain skipping in my bike. The bike is a KTM ultra Flite from 2010 with 9-speed cassette Shimano HG50, rear derailleur Shimano Deore XT Shadow and front derailleur Shimano Deore with 3 speeds. Some weeks ago I started to have the problem that when applying a lot of power to the pedals, the chain was slipping (not jumping to another gear but just slipping). This was particularly problematic when pedaling in up hill or when starting from still position. Since the chain was 5 years old and very worn out, and since the rear cassette was also worn out, I have bought and mounted the following new cassette and chain:

SHIMANO XT CS-M770 9-Speed Cassette 11-32

SHIMANO CN-HG93 9-Speed Chain

Right after having installed the new chain and new cassette everything was working great. I tested it inside a big garage and I could clearly test that even when applying high power to the pedals there was no more slipping issue. However, the day after, when actually biking on the road, the problem of chain slipping occurred again. If I stand will all my weight on the pedals but keep the bike still using the brakes, the new chain doesn´t skip. But as soon as I let the bike move and chain starts to move the problem occurs. When this happens, I can see the rear derailleur making a very abrupt and sudden move. I have of course done the synchronization (indexing) of the rear derailleur, so I do not have issues of the chain moving/staying in the wrong gear. When the chain skips during stress on the pedals, it doesn´t move to another gear. Now, I am wondering what could be the problem and how to solve it.

  1. Are the new rear cassette and chain that I have mounted ok/compatible with my bike and with the rear derailleur that I have? I would say so but am happy to hear your opinion on this.

  2. Could it be that I have applied too much oil on the chain and since the rear cassette is too oily this may cause again the slipping? I suspect this since right after mounting everything and applying the oil everything worked. At this point the new rear cassette was still very clean. But the day after, when biking for about 10km the oil I did put on the chain spread on the rear cassette. Obviously I have put too much oil, but can the excess oil in the cassette cause the issue I have?

  3. Or could it be that I need to replace also the rear derailleur with a new model? If yes, which one would you suggest that works well with the SHIMANO XT CS-M770 9-Speed Cassette and CN-HG93 9-Speed Chain?

  4. Any other possible cause for this issue and solution?

Below a photo of my current rear derailleur. It looks very dirty but this is before replacing rear cassette and chain.

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Addition: I add below some photos of the chainrings after having received comments that the chainrings could be too weared out. As you can see from the photos they are in very bad condition actually.

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UPDATE: After replacing all three chain rings with new ones the bike works now very well. I have tried biking on the road and applying high power to the pedals but was never able to make the chain skip. So it was definitively due to the chainrings. Thanks all for the help.

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    Try manipulating the chain with your hands, search if there's a "stiff link" that doesn't bend like the others.
    – Criggie ♦
    Commented Nov 22 at 20:13
  • Thanks! I will try this today.
    – spanito
    Commented Nov 23 at 5:06

4 Answers 4

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"Since the chain was 5 years old and very weared out and since the rear cassette was also wared out, I have bought and mounted the following new cassette and chain" sounds a lot like the chainrings are worn out too. Replacing them or at least the most used one or two should help.

Edit: The picture confirms it. The teeth on chainrings have worn into sharp and slightly asymmetric "shark fins" that are the hallmark of worn out chainring.

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  • Thanks a lot for your response, I can take a photo of the chainrings and, if allowed, I will add it to the original post. My bike has currently the Shimano M442 Octalink (44/32/22) chainrings, I have searched online and could not find this exact same model in the stores. Do you have nay suggestion on which moder chainrings I could buy that would work well in my bike?
    – spanito
    Commented Nov 23 at 4:59
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    @spanito Octalink is the BB model the crankset uses and is not important. You do not want to replace the whole crankset, that is expensive. And if yes, you would not need the same model. Here you have a diagram with part numbers si.shimano.com/en/pdfs/ev/FC-M442-2527/EV-FC-M442-2527.pdf The bolt diameters (BCD) you need to follow are 104 and 64 mm.
    – Vladimir F Героям слава
    Commented Nov 23 at 8:03
  • Thanks for the helpful information. I have now ordered the following chain rings. I think they should fit my crankset: rosebikes.se/… , rosebikes.se/… , rosebikes.se/shimano-deore-fc-m590t4060mt300-chainring-415858
    – spanito
    Commented Nov 23 at 12:14
  • Chainrings are now replaced and the chain no longer skips. Thanks a lot for helping me solving the issue.
    – spanito
    Commented Dec 1 at 9:25
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    @spanito you're welcome. Would you mark this answer as accepted so that the question won't keep popping up on the front page?
    – ojs
    Commented Dec 1 at 17:43
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Another thing to check is if the rear derailleur is square/aligned with the drivetrain. After 15 years, it is possible that the rear derailleur could have been bumped or impacted and this could result in less than ideal shifting or even skipping. The alignment can be assessed by eye usually by looking at the derailleur cage below the derailleur and judged whether it is in alignment with the drivetrain, or bent in or out. If bent, then a derailleur alignment tool can be used to bend the derailleur hanger into alignment.

Also, after 15 years of use, the pivots in a rear derailleur can build up some play, possibly enough that it becomes sloppy, which could impact the precision of the chain indexing.

ojs's answer is where I would first look: the front chainrings for wear. You now have a new chain and rear cassette, but the front chainring(s) did its time and it could be worn and worthy of replacement as well. A good way to test this would be to try your high-load testing in each of the three chainrings to see if the skipping occurs in all of them or only one or two of them. If it only occurs in some of them, it would point to the chainrings. If all of them, it does not rule out some other cause, but the chainrings should still be investigated.

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    @spanito saw your purchase on the other post. By all means, get some closeups (side view) of the wear on the chainring teeth you are replacing and add it to the question. It will prove useful to others looking to solve a similar issue in the future.
    – Ted Hohl
    Commented Nov 24 at 4:05
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    @spanito The Park CWP-7 looks to be a usable tool for your setup. Make sure you clean any/all grit away so the tool screws into the crankarm fully before using it. It can take some force. Review online videos of how to do it before trying it. Definitely chainring wear based on pictures - no doubt! I would limit the load placed on the chain until you get the chainrings replaced. Worn parts will wear a new chain much quicker, especially with a lot of load.
    – Ted Hohl
    Commented Nov 24 at 19:24
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    @spanito you will have to remove the crank to get the small ring off. The middle/large combination, maybe without removal (but it is easier removed). Clean, clean, clean that area first. 1. much nicer to work with (less messy). 2. you are going to need a full grip with your tools, and grit in a groove may limit how deep in the groove you get, so clean the grit out!
    – Ted Hohl
    Commented Nov 24 at 19:28
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    @spanito It looks like you will also need a Chainring Nut Wrench (Park CNW-2 parktool.com/en-us/product/…). You can see at that link how it is used with the hex key to hold the chainring nut. The small ring does not have chainring nuts, but the middle/big rings are mounted together and do use these nuts. Just loosening the hex without the CNW-2 "may" work, but tightening them back up upon reassembly may be questionable (the nut may spin and not tighten enough). And I will repeat, clean everything!
    – Ted Hohl
    Commented Nov 24 at 19:35
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    Yes I am no longer using the bike until the chainrings are replaced. I fully agree that otherwise I will damage the chain. Unfortunately, the replacement bike I have is super crappy but I will get the chainrings and cranck puller latest on Thursday so I count to be able to mount and test everything on Friday. I will update based on the results. Thanks again for the help, I am learning a lot.
    – spanito
    Commented Nov 24 at 19:42
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Regarding number 4, you might consider shifting down and pedaling faster instead of harder. When I was first getting into mountain biking I had a similar issues with chain skipping because I wasn't shifting down enough when climbing. Once I started shifting down before a climb, my chain stopped skipping.

Since you say the rear derailleur jumps, it could also be that one of the sprockets is gummed up and not moving smoothly or the chain is catching on the hanger somewhere. I also had a lot of chain skipping after a crash slightly bent my rear derailleur.

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  • The problem is that it was very hard to even start pedaling from still position or to pedal in any uphill. With the new chain and new crankset it is definitively better but still problematic. Until few months ago I could bike very fast applying a lot of power to the pedals, but not anymore. I will try first replacing the chainrings, but if this will not fully solve the issue then I will have to look into replacing the derailleur. I really hope not. I am not even sure which shimano model could I now mount in my bike since the original one is too old and will be not easy to find in stores.
    – spanito
    Commented Nov 24 at 13:49
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    @spanito Ted's advice is solid. Did you test the behaviour in the different chainrings? The large doesn't look too bad, the middle is badly worn, and the smallest quite alright from the little that is visible of it. An ounce of correct diagnosis >> unlimited pounds of the wrong cure.
    – WornChain
    Commented Nov 24 at 17:09
  • Yes, when the bike is moving I get a lot of chain skipping for both middle and large chainrings. The smalles is similar to new because I use it extremely rarely and I don´t have the skipping problem. If I put all my weight on the pedals with the bike still (using the brakes) then there is no skipping. Do you think this is a sign of issue with rear derailleur? I am of course willing to replace it if the problem is not solved also with the new chainrings, but what derailleur model would you suggest from shimano that is compatible with 9 speed cassette?
    – spanito
    Commented Nov 24 at 17:57
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    @spanito In that case, skipping in 2 worn rings and not the smallest, it sounds like the problem is in fact the chainrings. I would not worry about the deraileur before you have tried swapping those rings. It's a matter of preference (price, availability, needs), and shimano has a ok compatibility chart. productinfo.shimano.com/en/compatibility/C-433
    – WornChain
    Commented Nov 24 at 18:25
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Tension springs in deraileur worn or gummed up will cause this. As the chain bounces around when moving, it looses tension and jumps. As you tried, when the bike is stationary it doesnt jump.

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  • It's a possibility, my guess is that it's not really possible to just replace the spring. At the end of this week I should be able to test with new chainrings, if the issue is not solved yet I'll order also a new rear derailleur.
    – spanito
    Commented Nov 25 at 4:23

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