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  1. #1
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    Chain Skipping Mystery

    Really strange issue and I can't figure it out.

    I ride 32x20 on my 2015 Santa Cruz Carbon Highball with SRAM Rise 60 wheels. There is a Wolf Tooth 104 BCD stainless steel 32t ring up front, Chris King 18t stainless steel cog in the rear.

    Tried to switch to an 18t cog in the rear and despite perfect alignment the chain skips. By skip, I mean the chain rides up onto the top of the teeth on the rear cog then comes back down to the normal position. When the chain comes back down to the normal position, it feels like a ghost-shift on a gear bike (sudden slack being tensioned under power).

    It only happens under power.

    I've tried the following to solve it:
    • SRAM 8 speed chain
    • SRAM 9 speed chain
    • a different cog (different brand)
    • the same brand cog (Chris King) in 18t
    • adjusting the alignment (exaggerating each way)
    • using a Surly chain tensioner


    Frustrating thing is that it happens in all of the above combinations. It only stops when I put the 20t cog back on.

    Any ideas?

  2. #2
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    Bottom bracket flex? Is the chainring a N/W? If so, then it's holding the chain in place while sending it just out of alignment to the cog, which causes it to ride up?
    You're putting more power to the rear with the 18t than the 20t, which would cause more flex. Wonder if it would do it with a 19t?
    If you insist on needing 32/18 and can't make it work, 30/17 will give you virtually the same ratio, possibly without the current issues.

  3. #3
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    The chain ring is N/W but if that were the problem then would expect the same issue on the 20t cog (only happens with the 18t cog). Tempted to buy a new chain ring just to test the theor (non-NW, which are getting harder to get).

    It doesn't take much power to reproduce the problem, I can do it while seated pedaling and feathering the brake. Since I'm not applying much power I don't suspect bottom bracket flex, and again I'd expect the same problem even with the 20t (which works perfectly).

    Unfortunately I don't think I can experiment with 30/17 since the crank is 104 BCD.

    Tempted to drop it off at my LBS and ask them to install a new 18t cog and let them figure it out ;-)

  4. #4
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    Don't use derailleur chains. They are designed to slip off the cogs easily.

    I gave up on SRAM years ago. KMC these days.
    As little bike as possible, as silent as possible.
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  5. #5
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    Quote Originally Posted by Velobike View Post
    Don't use derailleur chains. They are designed to slip off the cogs easily.
    But they're not designed to slip over cogs easily, multi speed chains work great for ss IME. I wouldn't suspect frame/bb flex either. Are the chains you're trying new?

  6. #6
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    When you said you tried different chains, are the chains new? Seems like chain is not aligned lengthwise.


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  7. #7
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    the first chain was not new so I got a new one (SRAM 870) and had the exact same problem. Weird thing is that it works perfectly with two more teeth on the cog.

  8. #8
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    There has to be something different about the cog besides 2 less teeth to cause that issue IMO. If it were a repair in the shop I might try a different brand of chain (Shimano/KMC) and see what happens. Seems illogical but I have seen some chains that just didn't like a particular cog.

  9. #9
    Armature speller
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    If you wrap the chain around the cog, is it snug?

  10. #10
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    There's something missing from the equation.

    Your cogs are fine - I assume you've checked to make sure there's not a bent or bruised tooth on them.

    Your chainline is ok.

    So it's either the chain, or flex.

    If I got a single speed bike with a SRAM chain, I'd ditch it immediately. I have had endless trouble with them in the past and I'm not willing to risk them again. They never liked heavy grunt work.

    When you say you can reproduce it with gentle pressure, that raises another not so good option - check the chainstay isn't cracked.
    As little bike as possible, as silent as possible.
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  11. #11
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    The only difference really is the cogs, both are Chris King cogs, 20t (works) 18t (skips).

    The other difference would be chain length, since there is more play with the 18t cog installed. To account for the extra chain length I tried using a Surly chain tensioner, the problem happens both with and without the chain tensioner. I ran the chain tensioner for months without issues, until I tried it with the 18t cog.

    Frame Crack - hopefully the frame isn't cracked, it rides great with my 20t cog installed (did 20 miles yesterday) but I do have a small creak coming from the bike (not the BB, I just put in a new one).

    Chain - this could be the issue, and probably the cheapest experiment. Think I'll try this out.

    Half Links - FYI I learned that half links don't work with narrow-wide chain rings, at least not the ones I found at a LBS in Bend.

  12. #12
    Riding rigid
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    It sounds like the alignment is off just a little bit. With the 20t, there is no room to ride up, so you don't have issues. With the 18t, there is enough play to ride up the cog before falling back down. The tensioner, were you running it push up or push down? The tensioner would still allow the chain to ride up the cog since the tensioner usually doesn't help with alignment (there is play in the pulley). You didn't have issues with the tensioner before because you were still using the 20t.

    I'd move the cog position first; if your using multiple size spacers, it won't cost you a thing.

  13. #13
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    What kind of chain link connector are you using, and is it new as well?

    Wierd issue I have seen with a CK cog (only once) was that the cog moved fore and aft on the hub splines. It did not slip the chain, but did create a creak.

    Another thing on my bike was a pop sound that sounded like chain slip, but turned out to be worn hub bearings. Not sure if either is your issue, but something to think about. Good luck and post your solution!
    Vassago Cycles, Shadetree Bikes, Flat Tire Bikes, Galfer Brakes USA

  14. #14
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    Are you sure it is the chain skipping? As cstem points out, it could be skipping within the freehub.

    Are your 18T cogs new? A worn cog will develop burs on the edge of the teeth (you can feel with your fingernail). These can cause noise and/or weird chain suck or skipping issues, especially with a narrow chain.

  15. #15
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    pretty sure I can rule out the hub because it runs perfect with the 20t cog on. The 18t cog is new, I actually tried two, a brand new Surly 18t, and my buddy's Chris King 18t since it was the same manufacturer as my 20t cog.

    Going to get a new CK cog (so I can stop borrowing my buddy's) and a new KMC chain, then try again.

  16. #16
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    You don't get enough chain wrap with the 18t cog, but you do with the 20t. Combine that with a bit more tension on the chain with the 20t and voila, no skipping. Try going to a bigger chain ring instead of a smaller cog, or use a tensioner in the push-up orientation..

  17. #17
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    18t provides plenty of chain wrap, I can't skip the 11 on my geared bike no matter how hard I jam on it.

  18. #18
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    Quote Originally Posted by J.B. Weld View Post
    18t provides plenty of chain wrap, I can't skip the 11 on my geared bike no matter how hard I jam on it.
    With sliders/EBB or with a der mounted tensioner? A friend tried out SS on his Air9 RDO using a der hangar mounted tensioner. He borrowed my CK cogs, which do not skip on my Lynskey or MonoCog with sliding dropouts. On his bike, the 18t skipped. Badly. The 19t and 20t did not.

  19. #19
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    Quote Originally Posted by solo-x View Post
    With sliders/EBB or with a der mounted tensioner?
    Just a means to tension the chain and should be irrelevant to the issue. I don't know why your cog skipped on your friends bike but I do know that an awful lot of ss'ers use 18t cogs without any problems.

  20. #20
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    How long were the original chain and cog used? I find that if I've run a chain/cog combo for any real length of time the stretch/wear can make for a rough drivetrain when swapping cogs(depending on components) sometimes causing jumping. Best to change them at the same time.

  21. #21
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    Did you try taking a link or two out of the chain?

  22. #22
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    I have King 16 and 20 tooth cogs and both of them are really secure. The teeth are long and wide, so the chain has to be really loose to climb over a tooth. My chainring will drop the chain long before the cog will. I have an EBB, so I get plenty of chain-wrap even with a 16.

    Since you are using a tensioner, you may need to shorten the chain or use a half-link to get better chain-wrap. Using a 'push up' tensioner will also help (I think this is possible with Surly). On my old converted single speed I used a Gusset Slink half link to get the shortest chain possible, and then used a DMR STS tensioner in the 'push-up' position. A fixed tensioner like the DMR will be more secure, but require occasional adjustment. I would try shortening the chain before swapping the tensioner though since it's cheaper.

    If you have a picture of your setup it may help diagnose the issue.

  23. #23
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    If your chainline is right, and you are using proper cogs and chain designed for single speed use, then your chain tension can be extremely slack with your lower run of the chain almost hanging on the ground. (Take a look at pics of 3rd world bikes with enormous loads - usually the chain is just about dangling off)

    So unless your chainline is suspect or something is causing your chainstay to move to the side, tension is not the problem.

    As I said earlier there's something missing from the equation. Detailed pics may help.

    BTW have you checked the chain for a frozen or stiff link?
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  24. #24
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    Really appreciate all the replies!

    The chain line seems perfect, I'm using a steel ruler pressed against the chain ring and cog and it sits flush on both.

    I'm going to try again after buying a few parts and will reply back with results and pictures. Stay tuned ;-)

  25. #25
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    Quote Originally Posted by thunderpants View Post
    Really strange issue and I can't figure it out.

    I ride 32x20 on my 2015 Santa Cruz Carbon Highball with SRAM Rise 60 wheels. There is a Wolf Tooth 104 BCD stainless steel 32t ring up front, Chris King 18t stainless steel cog in the rear.

    Tried to switch to an 18t cog in the rear and despite perfect alignment the chain skips. By skip, I mean the chain rides up onto the top of the teeth on the rear cog then comes back down to the normal position. When the chain comes back down to the normal position, it feels like a ghost-shift on a gear bike (sudden slack being tensioned under power).

    It only happens under power.

    I've tried the following to solve it:
    • SRAM 8 speed chain
    • SRAM 9 speed chain
    • a different cog (different brand)
    • the same brand cog (Chris King) in 18t
    • adjusting the alignment (exaggerating each way)
    • using a Surly chain tensioner


    Frustrating thing is that it happens in all of the above combinations. It only stops when I put the 20t cog back on.

    Any ideas?

    Didn't go thru all the posts, but this is an easy one.


    King cogs have short teeth that allow chains to walk off the sprocket under power.

    Been there, done it.

    Get something like a Surly or Niner cog with tall teeth.



    King stuff is great, and I've got a number of their hubs, but their cogs are problematic in this way.

  26. #26
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    Got that covered already, I can reproduce the problem with a brand new Surly 18t cog.

  27. #27
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    Flexy frame?

    I've noticed that the larger the cog, the more tolerant it is of issues that may lead to skipping.

  28. #28
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    Had same issue with my sons ss, chain would jump under torque. All i run are ss setups on all my bikes, ended up being we needed a better tensioner. Put a pauls tensioner on it, and it never jumped again.

    That was on a new chain/ring and cog, alignment dead on. For whatever reason that frame liked the pauls

  29. #29
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    Bringing up old thread....

    For the past 2+ years I've been running a Surly Singulator on my 2014 Orbea Alma which I converted to SS shortly after I got the frame as a warranty replacement for my old Alma which I could use an EBB. This 2014 frame has a PF92 bottom bracket and I can't find any EBBs to fit it. That being said, I've really never had any issues with any gear combinations from 34:16 up to 34:19 with my Singulator.

    Last week I converted over to an oval Wolftooth 32t chainring and at the same time I replaced my cog with a new 16t Surly steel cog. I also replaced the chain with a new Ultegra chain... which is the same as what I've been running previously. Singulator stayed on bike with no adjustments between drivetrain swaps.

    With this set up I am having significant issues with the chain riding up the cog and then snapping back into place whenever I put any power down. Creating a similar ghost shift that I think the OP was referring too. I've since changed out the chain and cog to a used cog/chain combo that's has worked many times in the past. Same problem. I've adjusted the chain line several times trying to tweak things. No luck.

    The only thing I can think of that I haven't tried changing is the chainring. I can't seem to find if there are any issues with folks running an oval chainring and Singulator. Anyone have any experience with such a combo?

    Any advice would be much appreciated!
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  30. #30
    Armature speller
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    No issues running a Singulator in push up mode and 34,38,42/17 ovals on my CX bike.

  31. #31
    LDC is ded,deth by trollz
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    I use this tensioner with an oval....


    No issue ever
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    Ill be out riding, youll still be trolling mtbr. Mtbr, where people who dont ride come to pretend they do.

  32. #32
    LDC is ded,deth by trollz
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    Quote Originally Posted by NordieBoy View Post
    No issues running a Singulator in push up mode and 34,38,42/17 ovals on my CX bike.
    So the Garburuk worked!! Cheers

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    Ill be out riding, youll still be trolling mtbr. Mtbr, where people who dont ride come to pretend they do.

  33. #33
    Big Damn Hero
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    Ok thanks for the responses. But now that puts me back in square one... :-(
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  34. #34
    Armature speller
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    Quote Originally Posted by LaneDetroitCity View Post
    So the Garburuk worked!! Cheers

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    Yep, the 38 & 42 are quite good. The 34 is an AB.

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