# Chain jumping down the cassette when back pedalling



## aclinjury (Sep 12, 2011)

Ok on my Di2 R8050 system, I switched out a Shimano 11-28 cassette for an 11-30, and now whenever I ever back pedal and the chain is sitting in the big ring and the top 2-3 big cogs... the chain jumps 1 cog down the cassette. Chain will jump back up cassette to original position when I start to pedal forward again though.

Some more info:
the 11-28 cassette is a Dura Ace cassette from the previous generation (Di2 9000 series). The 11-30 cassette is from the current generation (Di2 8000). This shouldn't matter right.

What should I check?


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## cxwrench (Nov 9, 2004)

aclinjury said:


> Ok on my Di2 R8050 system, I switched out a Shimano 11-28 cassette for an 11-30, and now whenever I ever back pedal and the chain is sitting in the big ring and the top 2-3 big cogs... the chain jumps 1 cog down the cassette. Chain will jump back up cassette to original position when I start to pedal forward again though.
> 
> Some more info:
> the 11-28 cassette is a Dura Ace cassette from the previous generation (Di2 9000 series). The 11-30 cassette is from the current generation (Di2 8000). This shouldn't matter right.
> ...


Nothing. There is no derailleur guiding the chain onto the cog when you're pedaling backwards. The larger big cog you have the worse it will be. You can't do anything to stop other than not pedaling backwards.


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## tlg (May 11, 2011)

Only thing I can think of is; do you have drag in your freehub? If your freehub has drag, it could cause your chain to get some slack in it on top. At the extreme chainline, slack on top of your chain could cause it to slip off the cog.


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## aclinjury (Sep 12, 2011)

ok after mucking around and following the Shimano's instructions, I found that everything was already set pretty much like it should be. So I put the 28t cassette back on and put the chain in big-big combo and back pedal, and sure enough, chain does jump down the cassette. But this only happens in big-big for the 28t cassette, not in any other combo. Maybe I have never noticed this since I never ride in big-big combo (you're not supposed to cross-chain that much right!).

So I put back on the 32t cassette, and tried back-pedal in big-big combo, chain jumped agian, as expected. Shift down one cog and back pedal, chain still jumped down. Shift down another cog and back pedal again, this time the chain did try to jump down (I could hear it), but it didn't so it at least held position.

Hub is smooth, freehub is smooth.

I guess CX is right! don't pedal backwards when cross-chaining when in big-big combo or near to it. I usually I don't pedal backwards except when sometimes I unclip at a stop and thus will pedal half a revolution backwards to put a foot down.

I think it also doesn't help that the chainstays of this bike is only 401mm long, making the chain angle really bad when you're cross chaining


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## No Time Toulouse (Sep 7, 2016)

You should not be using the big-big combination......

BTW, did you get a chain that was 2 links longer? Your chain is probably too short.


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## blackfrancois (Jul 6, 2016)

patient: doc, it hurts when i do this ...

doctor: don't do that.


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## cxwrench (Nov 9, 2004)

No Time Toulouse said:


> *You should not be using the big-big combination......*
> 
> BTW, did you get a chain that was 2 links longer? Your chain is probably too short.


This is complete bullshit, I really wish people that post this would stop. EVERY modern drivetrain is designed to work in big/big.


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## duriel (Oct 10, 2013)

How fast can you go backpedaling? I think you'll go faster in the little/little, try that and see how fast u can go and get back to us!


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## .je (Aug 25, 2012)

Mine was like that too, at one point it was pretty bad. 
I replaced the chain with a new one, since it was due, but not _that_ bad... I thought...

2 things were different this time: 
i) the old chain was, I thought, maybe one link too short, so the tension was high. There was only a few degrees movement in the derailleur in the big-big, if I did that. I thought, maybe, that any extra tension might be pulling on it, and it can only be upulled down. The new one is 2 links longer, and it shifts very precisely now. I can also backpedal NP.
ii) the old chain, even oiled, didn't seem to turn on the pins _as_ smoothly as the new chain, so any binding might pile up, and pop it off the big ring.

I _could_ have been right, but not sure which might have been the bigger effect. I can say for sure that my backward FTP has gone up almost 20W from before, so you might want to consider.


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## cxwrench (Nov 9, 2004)

.je said:


> Mine was like that too, at one point it was pretty bad.
> I replaced the chain with a new one, since it was due, but not _that_ bad... I thought...
> 
> 2 things were different this time:
> ...


Doesn't matter if the chain is moving backwards. The derailleur has NO effect on the chain at that point. The ONLY reason the chain comes off when you backpedal is because there is no pulley guiding it on to the cog. The tension on the chain is the same.


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## aclinjury (Sep 12, 2011)

cxwrench said:


> Doesn't matter if the chain is moving backwards. The derailleur has NO effect on the chain at that point. The ONLY reason the chain comes off when you backpedal is because there is no pulley guiding it on to the cog. *The tension on the chain is the same*.


ok, the tension on the top part of the chain is the same. But what about the tension on the bottom part of the chain? It's not the same right? I'd think that with a shorter chain, then the tension on the bottom part of the chain (when in big-big combo) would be higher than if the chain was longer right? Well then, could the higher tension on the bottom part of the chain may be acting like a resistance force for the chain to move backwards? and thus causing the chain to jump? I'd think a looser chain would allow the chain to move backwards with less resistance and thus may alleviate the jumping (maybe not totally prevent it).

I suppose I can prove whether this is true or false by breaking the chain loose (quick link) and then roll it backwards while it's loose not rolling thru the rear derailleur (except for the top pulley) and see if it'll jump. If it doesn't jump, then maybe derailleur tension and thus chain length maybe be a mitigating factor?


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## evan326 (Jan 16, 2017)

All are capable, but I thought only SRAM was designed for it. Shimano still says don't do it right?


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## aclinjury (Sep 12, 2011)

evan326 said:


> All are capable, but I thought only SRAM was designed for it. Shimano still says don't do it right?


SRAM was designed for it? how? Like CX said, there is no guide (eg, a pulley guide) to keep the chain rolling straight when its moving backwards like there is a lower pulley to guide it straight when moving forward. I would think that chainline is the main determinant if a chain will jump when backpedaling, and chainline will depend on bike geometry (eg, chainstay length)


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## tlg (May 11, 2011)

No Time Toulouse said:


> You should not be using the big-big combination......


Meh. Says you. I live in a hilly area. I use big big all the time. And get well over 5,000mi out of a chain.



evan326 said:


> All are capable, but I thought only SRAM was designed for it. Shimano still says don't do it right?


Yes, all are capable. Shimano doesn't say don't do it. They recommend against it for two reasons:
a) it's less efficient
b) increases wear

So as long as you don't mind losing a couple watts or a few miles on the life of your chain, there's no reason not to do it.

This is what the big 4 mfg's say about it.
Cross-chaining: is it really all that bad? | road.cc


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## Jay Strongbow (May 8, 2010)

Does your bike have really short chain stays?

My experience with two identical groups on different bikes indicates short chain stays is a factor. 
I don't think it's anything to 'fix' per se. It just happens and really isn't a problem.


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## tlg (May 11, 2011)

Jay Strongbow said:


> Does your bike have really short chain stays?


Which bike? I have a bunch. 

Mine are all, or have been, 54-56cm. And my wife rides 50-52. Never had an issue on any bike.


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## Jay Strongbow (May 8, 2010)

tlg said:


> Which bike? I have a bunch.
> 
> Mine are all, or have been, 54-56cm. And my wife rides 50-52. Never had an issue on any bike.


I was responding to the OP. And asked him about chain stay length not bike size.


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## tlg (May 11, 2011)

Jay Strongbow said:


> I was responding to the OP. And asked him about chain stay length not bike size.


Oh. Well you responded to my post.


OP said previously "the chainstays of this bike is only 401mm long"


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## Lombard (May 8, 2014)

No Time Toulouse said:


> BTW, did you get a chain that was 2 links longer? Your chain is probably too short.


If the chain spins in the large/large combo without binding, it is NOT too short.


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## Kerry Irons (Feb 25, 2002)

aclinjury said:


> ok, the tension on the top part of the chain is the same. But what about the tension on the bottom part of the chain? It's not the same right? I'd think that with a shorter chain, then the tension on the bottom part of the chain (when in big-big combo) would be higher than if the chain was longer right? Well then, could the higher tension on the bottom part of the chain may be acting like a resistance force for the chain to move backwards? and thus causing the chain to jump? I'd think a looser chain would allow the chain to move backwards with less resistance and thus may alleviate the jumping (maybe not totally prevent it).
> 
> I suppose I can prove whether this is true or false by breaking the chain loose (quick link) and then roll it backwards while it's loose not rolling thru the rear derailleur (except for the top pulley) and see if it'll jump. If it doesn't jump, then maybe derailleur tension and thus chain length maybe be a mitigating factor?


You're trying to infuse this "problem" with issues that are tangential at best. Re-read what CX said in his first post: when you backpedal, there is no derailleur keeping the chain from trying to align with the front ring so it will naturally try to get the chain on a smaller cog. It makes virtually no difference what your setup is. Get that in your head and stop backpedalling. Not sure why you are backpedalling in the first place.


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## cxwrench (Nov 9, 2004)

Lombard said:


> If the chain spins in the large/large combo without binding, it is NOT too short.


Not necessarily true. Depends on what your idea of 'too short' is. If the derailleur is pulled all the way forward but still works, I'd personally call that too short. I'm guessing your definition of too short would be ripping the derailleur off the bike. Semantics.


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## Lombard (May 8, 2014)

cxwrench said:


> Not necessarily true. Depends on what your idea of 'too short' is. If the derailleur is pulled all the way forward but still works, I'd personally call that too short.* I'm guessing your definition of too short would be ripping the derailleur off the bike. Semantics.*


Pretty much, yes. If it spins freely in large/large, it's OK in my definition. But remember, I'm the guy who favors small/small over large/large.


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## Lombard (May 8, 2014)

cxwrench said:


> This is complete bullshit, I really wish people that post this would stop. EVERY modern drivetrain is designed to work in big/big.


I'm going to reply to this at the risk of a virtual flogging by you, CX.  

My take is, sure, if adjusted correctly, it should work. But unless you are a racer who doesn't want to downshift the front for fear of losing a fraction of a second, is the large/large ever really necessary or practical?

I favor the smaller ring over the larger ring for a couple reasons:

1) It is quieter.
2) If I suddenly do need that smaller ring, I am more likely to drop a chain if I am already in the largest cog.

Generally, I use neither extreme. It is unnecessary. I go to the large ring if my chain starts chattering against the FD. That is usually not until the smallest cog. When I need easier gearing for climbing or if I am stopping, I will go back to the small ring before going to considerably larger cogs.


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## .je (Aug 25, 2012)

Kerry Irons said:


> You're trying to infuse this "problem" with issues that are tangential at best.


Nice play on words.
What I read from that post was saying, if I'm trying to make sense of that thinking, is that the derailleur is holding the bottom in the right place, but the top is held on the chainline between the chainring and the large cog, which is sort of pulling it outward, if there's tension. 
Is that what was meant? It really shouldn't be able to have enough to pull off the teeth. Apols if that's completely off (play on words again).


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## aclinjury (Sep 12, 2011)

.je said:


> Nice play on words.
> What I read from that post was saying, if I'm trying to make sense of that thinking, is that the derailleur is holding the bottom in the right place, but the top is held on the chainline between the chainring and the large cog, which is sort of pulling it outward, if there's tension.
> Is that what was meant? It really shouldn't be able to have enough to pull off the teeth. Apols if that's completely off (play on words again).


yeah that's what I meant, I probably didn't explained it all that well.
Either way, I've been able to verified to myself that tension thru the derailleur makes no difference. So I broke the chain up (quick link), and proceeded to roll it backwards in the top 2 "big-big" combos, and of course with no chain tension, and sure enough the chain did jump too.


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## aclinjury (Sep 12, 2011)

Kerry Irons said:


> You're trying to infuse this "problem" with issues that are tangential at best. Re-read what CX said in his first post: when you backpedal, there is no derailleur keeping the chain from trying to align with the front ring so it will naturally try to get the chain on a smaller cog. It makes virtually no difference what your setup is. Get that in your head and stop backpedalling. Not sure why you are backpedalling in the first place.


I got it now, and have confirmed what CX and you just said.
I'm not backpedaling intentionally. But sometimes at a stop I backpedal half a rev to unclip and put my foot down. I have 4 other bikes that don't do this in big-big, only this one bike, so I never thought about it until now on this bike.


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## aclinjury (Sep 12, 2011)

Jay Strongbow said:


> Does your bike have really short chain stays?
> 
> My experience with two identical groups on different bikes indicates short chain stays is a factor.
> I don't think it's anything to 'fix' per se. It just happens and really isn't a problem.


chainstays are 401mm. When I'm in big-big, with 52t chainring upfront and largest cog 32t on back, the chainline angle does look a tad more extreme than all my other bikes, which have 405-410mm chainstays. So probably this is the dominant a factor causing all this. It is what it is. Need to just not backpedal when in big-big


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## evan326 (Jan 16, 2017)

aclinjury said:


> SRAM was designed for it? how? Like CX said, there is no guide (eg, a pulley guide) to keep the chain rolling straight when its moving backwards like there is a lower pulley to guide it straight when moving forward. I would think that chainline is the main determinant if a chain will jump when backpedaling, and chainline will depend on bike geometry (eg, chainstay length)


I was referencing cross chaining, sram red 22 is stated to work with all 22 gears.


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## No Time Toulouse (Sep 7, 2016)

cxwrench said:


> This is complete bullshit, I really wish people that post this would stop. EVERY modern drivetrain is designed to work in big/big.


But not if he shortened the chain to it's limit, then added larger cogs...which it seems he did.


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## cxwrench (Nov 9, 2004)

Lombard said:


> Pretty much, yes. If it spins freely in large/large, it's OK in my definition. But remember, I'm the guy who favors small/small over large/large.


Aaarrggghhhhh


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## Jay Strongbow (May 8, 2010)

Lombard said:


> Pretty much, yes. If it spins freely in large/large, it's OK in my definition. But remember, I'm the guy who favors small/small over large/large.


Probably fine on a steel or Ti bike where the hanger is part of the frame. Not so fine to stress a light alloy hanger. They can fatigue and eventually break (even from routine use without any extra force to squeeze into big/big) and that added stress won't help them last any longer.


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## Lombard (May 8, 2014)

Jay Strongbow said:


> Probably fine on a steel or Ti bike where the hanger is part of the frame. Not so fine to stress a light alloy hanger. They can fatigue and eventually break (even from routine use without any extra force to squeeze into big/big) and that added stress won't help them last any longer.


So you're saying a looser chain is easier on the derailleur hanger? This would be another reason not to use large/large if this is the case. But I doubt it makes any real world difference.


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## velodog (Sep 26, 2007)

Lombard said:


> So you're saying a looser chain is easier on the derailleur hanger? This would be another reason not to use large/large if this is the case. But I doubt it makes any real world difference.


Large\large don't hurt nearly as much as many would have us believe.


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## Jay Strongbow (May 8, 2010)

Lombard said:


> So you're saying a looser chain is easier on the derailleur hanger? This would be another reason not to use large/large if this is the case. But I doubt it makes any real world difference.



No. There is no such thing as a 'looser' chain if you are not going to the limits of the der. spring which is the smart way to measure your chain. The der. keeps chain tension constant in any gear. But when you go "all the way forward" as CX phrased it and you seem to think is fine you stress the hanger.


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## Lombard (May 8, 2014)

velodog said:


> Large\large don't hurt nearly as much as many would have us believe.


I didn't say it would hurt. My point is that for most of us, it's impractical and unnecessary. 



Jay Strongbow said:


> No. There is no such thing as a 'looser' chain if you are not going to the limits of the der. spring which is the smart way to measure your chain. The der. keeps chain tension constant in any gear.* But when you go "all the way forward" as CX phrased it and you seem to think is fine you stress the hanger.*


I see your point here. However, if you never use large/large, it's basically irrelevant.


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## Jay Strongbow (May 8, 2010)

Lombard said:


> I see your point here. However, if you never use large/large, it's basically irrelevant.


With a choice between cutting my chain correctly and not being able to use all the gears I'm carrying around I'd just cut my chain correctly. But whatever works for you.


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## velodog (Sep 26, 2007)

Lombard said:


> Pretty much, yes. If it spins freely in large/large, it's OK in my definition. But remember, I'm the guy who favors small/small over large/large.


Small\small holds no interest for me. I'll go large\large because that's usually short term, but finding my way to small\small usually means that the struggle is ending so I'll have shifted to the large ring before then.

Choice is good, luckily we all get to make our own.


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## Jay Strongbow (May 8, 2010)

velodog said:


> Small\small holds no interest for me.


I use it quite a bit on hills that start out needing the small ring, then flatten out so speed up, when I'm hanging on by the skin of my teeth and switching to big ring and rear shifting would be enough to pop me off the back.


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## aclinjury (Sep 12, 2011)

well guys, after some further inspection of the bike, I have also ruled out that my chain is not long enough. It is long enough.

My "issue" (which is really isn't an issue) boils down to 2 things:
1. relatively short chainstays
2. narrowness of 11 spd chain

why do I say this? Because, like I mentioned before, shorter chainstays give an exaggerated chainline angle. And the narrow 11 spd drivetrain means that tolerance between cogs and chain is tight. So combine a higher chain angle with tight chain/cog tolerance, it means that backpedaling will cause the cogs to want to make the chain jump.

On my other bikes, they're all 10 speed and with longer chainstays. And this is why I don't experience backpedal issue on the other bikes because their chains have more room to move about between the cogs (thus the cogs don't cause chain to jump). So that's that, I think I got it right, right?? Solution is don't backpedal eh. But, hey, sometimes I backpedal (by raising my foot) half a revolution to either get my foot in a ready position (3- or 9- o'clock), or I might backpedal half a rev backwards to put my foot down as I unclip. So I just have to make sure I'm not in the big chainring while also in the 1st or 2nd cogs (top biggest ones)


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## cxwrench (Nov 9, 2004)

aclinjury said:


> well guys, after some further inspection of the bike, I have also ruled out that my chain is not long enough. It is long enough.
> 
> My "issue" (which is really isn't an issue) boils down to 2 things:
> 1. relatively short chainstays
> ...


You've got it :thumbsup:


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## GlobalGuy (Jun 9, 2015)

cxwrench said:


> This is complete bullshit, I really wish people that post this would stop. EVERY modern drivetrain is designed to work in big/big.


I'm certainly not an expert on bikes, (which is one reason I never work on them), but I wish what you state could be communicated to my individual bike and specifically its front derailleur.


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## Jay Strongbow (May 8, 2010)

GlobalGuy said:


> I'm certainly not an expert on bikes, (*which is one reason I never work on them*), but I wish what you state could be communicated to my individual bike and specifically its front derailleur.


You probably should start then because your mechanic doesn't seem to be able to handle something I'm sure you could.


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## Kerry Irons (Feb 25, 2002)

aclinjury said:


> So I just have to make sure I'm not in the big chainring while also in the 1st or 2nd cogs (top biggest ones)


When I'm rolling up to a stop, I shift to the small chainring. I know I'll get away from the stop more quickly when I'm in the proper gear.


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## Lombard (May 8, 2014)

Kerry Irons said:


> When I'm rolling up to a stop, I shift to the small chainring. I know I'll get away from the stop more quickly when I'm in the proper gear.


Sounds like a no-brainer to me. :thumbsup: Small ring and 5th cog works for me unless I'm stopped on a hill.


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## aclinjury (Sep 12, 2011)

Kerry Irons said:


> When I'm rolling up to a stop, I shift to the small chainring. I know I'll get away from the stop more quickly when I'm in the proper gear.


well I also have a fun habit of trying to do a track stand if I know the light is about to turn green or if I'm not planning to put a foot down at a stop, rather not muck around with front shifting


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## Methodical (Jul 21, 2012)

cxwrench said:


> This is complete bullshit, I really wish people that post this would stop. EVERY modern drivetrain is designed to work in big/big.


I know I use mine when necessary or whenever I feel like it and I don't spend .0000000000001 thinking about it.

I'll use whatever combination I need to get me there. That's what those gears are there for.

At least now I don't have to hear that chain rub anymore with the SRAM yaw FD.


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## aclinjury (Sep 12, 2011)

update to my post:

well I have since changed out the 11-spd Yaban (Taiwan) chain with a Shimano 11-spd Dura Ace/XTR chain, and my issue has been COMPLETELY resolved! Amazing.

I did measure the width of the Yaban chain and it's exactly the same width as the Shimano chain. So chain widths are the same. However, the difference (however slight) is in the pattern of the notches at the end of each link! Apparently, Shimano cassette really needs a Shimano chain for completely smooth operation. Back pedaling while completely cross-chained no longer cause any chain dropping/skipping. 
There you go. Lesson learned for me.


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## cxwrench (Nov 9, 2004)

aclinjury said:


> update to my post:
> 
> well I have since changed out the 11-spd Yaban (Taiwan) chain with a Shimano 11-spd Dura Ace/XTR chain, and my issue has been COMPLETELY resolved! Amazing.
> 
> ...


Huh...I'm surprised that it made that much difference but glad to hear it. Good job figuring it out!


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## aclinjury (Sep 12, 2011)

cxwrench said:


> Huh...I'm surprised that it made that much difference but glad to hear it. Good job figuring it out!


I'm also surprised that it made that much of a difference!

I think it made a difference in this case because in this particular case the frame has a shorter than usual chainstays (under 400mm), and this give the chainline a huge angle when crossed-chain. And couple with the tight tolerances of 11-spd drivetrain, backpedaling is no bueno! I think if the chainstays were a bit longer, like 410-415mm, then the Yaban chain would have been fine. 

So lesson for me is, when tolerances are supertight, use all components from the same manufacturer. It's amazing how much smoother the Shimano chain is now.


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## Jay Strongbow (May 8, 2010)

aclinjury said:


> I'm also surprised that it made that much of a difference!
> 
> I think it made a difference in this case because in this particular case the frame has a shorter than usual chainstays (under 400mm), and this give the chainline a huge angle when crossed-chain. And couple with the tight tolerances of 11-spd drivetrain, backpedaling is no bueno! I think if the chainstays were a bit longer, like 410-415mm, then the Yaban chain would have been fine.
> 
> So lesson for me is, *when tolerances are supertight, use all components from the same manufacturer. * It's amazing how much smoother the Shimano chain is now.


To quote myself from earlier "My experience with two identical groups on different bikes indicates short chain stays is a factor."

Back when I was using the bike with super short chainstays I was using mostly 10 speed Ultegra chains. And now that I think of I seem to recall the skipping while backpedaling would only happen, or happen more and easier, when my chain was in need of a lube job. 

I don't know that "same manufacturer" is necessarily it and it's more like "better" (I'd guess switching to a high end KMC or Sram would have had the same results and Sora wouldn't) but whatever, I think generally you got it.


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## aclinjury (Sep 12, 2011)

Jay Strongbow said:


> To quote myself from earlier "My experience with two identical groups on different bikes indicates short chain stays is a factor."
> 
> Back when I was using the bike with super short chainstays I was using mostly 10 speed Ultegra chains. And now that I think of I seem to recall the skipping while backpedaling would only happen, or happen more and easier, when my chain was in need of a lube job.
> 
> I don't know that "same manufacturer" is necessarily it and it's more like "better" (I'd guess switching to a high end KMC or Sram would have had the same results and Sora wouldn't) but whatever, I think generally you got it.


that's right my mang, you got it. Well, I sort of suspect that it could be the Yaban chain (a high end chain, not some el cheapo one) could just be slightly "not the same" as the Dura Ace chain. But at the time of this issue, I had just bought the Yaban chain and I was hoping myself that chain was not the issue, besides the Yaban chain is gold-plated which was one reason why I went for its bling factor. Well fast forward 5-6 months, since then I have had more time to examine the bike, examine its chainline angle, took measurements of the bike's chainstays, tried on a few different wheelsets and different cassette sizes (11-25, 11-28, 11-30), even tried different bottom brackets thinking that maybe bearing-cup width may be differnt and thus affecting chainline angle. 

And just about the ONLY things left to try was 1) chain, or 2) a completely crankset. Well, I wanted to keep the current crankset so I was less inclined to try another crankset. So I bought the Dura Ace chain to try. At first I didn't think Dura Ace chain would solve the issue because my initial superficial inspection of the Dura Ace chain and the Yaban chain was that the 2 chains looked pretty much the same to my eyes. Lo and behold, after installing the Dura Ace chain, it was a "Eureka" moment. Problem solved.

I still believe if I was using a 10-spd drivetrain then this issue would not happen or happen at a much lesser extent due to looser tolerances of 10spd drivetrain.


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