# Chain falling off small ring



## Big Red Bianchi (Sep 11, 2009)

I have a problem with my chain falling off the lower ring. LBS cannot figure out the problem so I thought I'd get some info here.

Here's what I have:

Bianchi Sempre

DA 7800 front derailleur; 7800 rear derailleur; 7800 shifters; 7800 cassette (12-25); and a Shimano chain, not sure of the model, but LBS checked it. Model is OK, wear is OK.

FSA Gossamer BB30 Compact 50/34 crankset

When I shift from the larger ring to the smaller ring, the chain sometimes just falls off to the left (inside) of the small ring. I have a 'dogtooth' there, but the chain just ends up on top of that.

LBS showed me that the front derailleur is adjusted correctly. If anything, it's almost too far to the right. (IE the chain almost rubs the derailleur when on the small ring.)

However, for some reason, when I shift from the large ring to the small ring it's moving the chain too far to the left. If I pedal slowly, I can actually see the chain move to the inside/left of the small ring, then either continue and fall off, or catch and move very slightly back to the right, and center on the small ring.

Does that make sense?

I know it's difficult to troubleshoot without seeing this in person, but I've tried to describe everything.

Any thoughts or suggestions would be greatly appreciated.

THANKS!

-Bianchi Bob


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## 202cycle (Sep 13, 2011)

If the chain is landing on top of the, "Dog tooth", might I suggest moving that thing up just a bit. This tends to be an issue with compact cranks. The other thing is to soft pedal while downshifting in the front.


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## jnbrown (Dec 9, 2009)

This:

Road - K-Edge Chain Catchers


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## JCavilia (Sep 12, 2005)

202cycle said:


> If the chain is landing on top of the, "Dog tooth", might I suggest moving that thing up just a bit. This tends to be an issue with compact cranks. The other thing is to soft pedal while downshifting in the front.


+1. The Dog Fang, if adjusted correctly, should prevent the chain from leaving the small ring. Try moving it higher. With the chain on the small ring and the largest cog, move the thing to where it almost touches the chain, with its bottom edge at the same height as the bottom edge of the chain link. You need it really close if you put it high, because the device has a little flex, and if the chain hits it hard it can sometimes push it over enough to squeeze past and end up underneath, which is a nuisance.

That 16-tooth jump can be troublesome. IMO it makes for a weird gear pattern, too. Changing that 50 to a 48 would improve both factors.


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## Big Red Bianchi (Sep 11, 2009)

jnbrown said:


> This:
> 
> Road - K-Edge Chain Catchers



Looks nice, but a bit expensive.

Do they work well? Better than the dogtooth?

thanks,


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## jnbrown (Dec 9, 2009)

Big Red Bianchi said:


> Looks nice, but a bit expensive.
> 
> Do they work well? Better than the dogtooth?
> 
> thanks,


There are a few cheaper knock off versions.
Do a search on chain catcher.
I look at it as cheap insurance.
Yes they work, never had a problem since installing on multiple bikes.
You will never have a dropped chain or worry about it when shifting.
They fit any bike where the dog fang type only fit certain frames, I guess you don't have that problem, but maybe you do if you can't get it to work right.


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## onespeedbiker (May 28, 2007)

My first thought is if the chain is directional and may have been installed backwards. Is this the result of some change or upgrade? Did you buy the bike in it's current setup? Did it previously work before or has the chain always slipped off the small CR?


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## orange_julius (Jan 24, 2003)

Big Red Bianchi said:


> I have a problem with my chain falling off the lower ring. LBS cannot figure out the problem so I thought I'd get some info here.
> 
> Here's what I have:
> 
> ...


Front der is set up too high?


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## Big Red Bianchi (Sep 11, 2009)

onespeedbiker said:


> My first thought is if the chain is directional and may have been installed backwards. Is this the result of some change or upgrade? Did you buy the bike in it's current setup? Did it previously work before or has the chain always slipped off the small CR?


Chain is fine. LBS double checked to make sure it's installed correctly. (Actually two different LBS both double checked.)

I had a Bianchi Mono-Q with 105 that had a 50-34 crank and had this problem once in a while.

The new bike seems to do this more often. Mono-Q may have fallen off one out of maybe 30 downshifts, the Sempre seems to fall off about one out of maybe 10.

If I'm paying attention and slow pedal, I can just about keep the chain on all the time, but I'm not always doing that....


I've ordered the k-edge chain guard, and thinking about a different crank.

Someone mentioned that a 16 tooth change is a lot, and this happens often with compact rings.


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## jnbrown (Dec 9, 2009)

I would install the K-edge before buying a new crank.
It should solve the problem completely and you can pedal normally and shift at will.
The worst that can happen is the chain won't engage onto the smaller ring.
If this happens then you have other problems.
there are tons of people riding 50-34 without any problem.


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## Big Red Bianchi (Sep 11, 2009)

jnbrown said:


> I would install the K-edge before buying a new crank.
> It should solve the problem completely and you can pedal normally and shift at will.
> The worst that can happen is the chain won't engage onto the smaller ring.
> If this happens then you have other problems.
> there are tons of people riding 50-34 without any problem.


Yes, I'll definitely try the K-Edge for a few weeks.  If I'm still having problems (which I can't imagine I will be...) I'll start thinking about a new crank.

The other thing I'm looking at is a DA 7900 front der.


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## JCavilia (Sep 12, 2005)

Big Red Bianchi said:


> Yes, I'll definitely try the K-Edge for a few weeks. If I'm still having problems (which I can't imagine I will be...) I'll start thinking about a new crank.
> 
> The other thing I'm looking at is a DA 7900 front der.


Should do it, but if not, you don't necessarily need a new crank. You can change just the rings.


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## onespeedbiker (May 28, 2007)

Big Red Bianchi said:


> Chain is fine. LBS double checked to make sure it's installed correctly. (Actually two different LBS both double checked.)
> 
> I had a Bianchi Mono-Q with 105 that had a 50-34 crank and had this problem once in a while.
> 
> ...


I had a Shimano setup and it never dropped a chain, however I was careful when shifting.The primary issue may be to think ahead and don't shift into the small chainring at the last moment. The one issue with a compact crank is as you said, the 16t difference. This means if you shift with too much pressure on the pedal the chain will, first need more over-shifting to pull the chain off the big chainring and second, sometimes cause the chain to skip over the small chainring when it doesn't immediately mesh with the small chainring teeth, as the crank rotation sudden increasing when you shift. In the past a 16T jump was common with touring bikes, but friction shifting shifts the chain slower than index and cyclist expected less from their components than they do today, so they were more careful when shifting.


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## PoorCyclist (Oct 14, 2010)

I had the K edge and still was able to have the chain fall on the frame in the area in front of the catcher. I guess I could have pedalled and it may have come back on, but it may also chain suck to cause more damage in the back.

I know your LBS checked but you could make sure the derailleur is mounted as low as possible and the tension on the cable is not too high. This should decrease the chance of chain drop from 3% to even less,

I have had the Gosammer compact for thousands of miles and no drop on Shimano. On my new bike with SRAM I was not so lucky.

The 7900 FD will not be an upgrade as the pull ratio is not compatible unless you also get a ST-7900 shifter.


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## Mr. Versatile (Nov 24, 2005)

Anybody know of a dog tooth that will fit on a Giant Defy Advanced? There's not a round tube on the bike including the seat post, and especially the seat tube.


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## reptilezs (Aug 21, 2007)

chainrings not clocked right. der cage spread open. bent tooth


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## Cyclin Dan (Sep 24, 2011)

Mr. Versatile said:


> Anybody know of a dog tooth that will fit on a Giant Defy Advanced? There's not a round tube on the bike including the seat post, and especially the seat tube.


Does it have a breeze on derailleur mount?


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## wim (Feb 28, 2005)

*Another possibility.*



Big Red Bianchi said:


> LBS showed me that the front derailleur is adjusted correctly. If anything, it's almost too far to the right. (IE the chain almost rubs the derailleur when on the small ring.)


While this sounds like it is adjusted correctly, it may not be. I sometimes see front derailleurs which do not rest on the low limit screw, but are hanging on the tight cable instead. The only way to make absolutely sure that the low limit is adjusted correctly is to loosen, or even better, remove the cable, then check chain-to-cage plate clearance.

For some reason, many mechanics adjust the low limit screw on a front derailleur with the cable attached, merely assuming the cable is loose enough. The instructions are clear: low limit _before_ you attach the cable.


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## mauiguy (Sep 7, 2011)

I agree if the tension of the shift cable is to high the deraillier will pull violently back towards the frame sending the chain further inboard then you need.


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## onespeedbiker (May 28, 2007)

mauiguy said:


> I agree if the tension of the shift cable is to high the deraillier will pull violently back towards the frame sending the chain further inboard then you need.


It's not that the cable tension will violently pull the derailleur cage back toward the frame, the spring in the derailleur does the movement. The problem is if the cable is to tight, it may be adjusted past the trim adjustment click, meaning it will overshift all the way to the inside derailleur stop, rather than stop where the trim adjustment stop should be.


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## sometimerider (Sep 21, 2007)

Two factors that can make the problem worse:

1. Short chain stays (not much you can do about this).

2. Shifting to the small ring when the chain is on (or near) the largest cog in back. It helps to be in a smaller cog - the smaller the better.


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## kbwh (May 28, 2010)

IIRC OP's Sempre is a 61 with 410 mm chain stays. Hardly the culprit.

I'd go with what wim writes.


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## Big Red Bianchi (Sep 11, 2009)

mauiguy said:


> I agree if the tension of the shift cable is to high the deraillier will pull violently back towards the frame sending the chain further inboard then you need.


Boy that certainly seems like what's happening. When I'm on the big ring, and I click the shifter to move to the small ring, there's a pretty violent POP, like something was under a lot of pressure and SNAPPED to the new position.


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## wim (Feb 28, 2005)

Big Red Bianchi said:


> Boy that certainly seems like what's happening. When I'm on the big ring, and I click the shifter to move to the small ring, there's a pretty violent POP, like something was under a lot of pressure and SNAPPED to the new position.


Big Red and you misunderstand how front derailleurs work. As said by onespeedbiker, it's not the tension of the cable pulling the cage into the frame. A strong spring in the front derailleur is trying to force the cage into the frame at all times. When you release wire in the shifter, that spring releases its energy and snaps the derailleur cage into the direction of the frame. Compare it to pulling the trigger on a gun.

BTW, that "pretty violent pop" is perfectly normal with Shimano STI. IMO, it's not that good a design because you have zero control over the speed and force of the cage movement into the frame.


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## PoorCyclist (Oct 14, 2010)

On the Shimano and some SRAM year models they have a trim in the shifter to move the cage inboard a bit. If you "activate" this first it would release some of the tension then the shift to the small ring is much more gentle

Also if you set the cable tight enough, when you use this trim, the cage won't move on the Shimano.... (but it doesn't take much) in my tinkering experience this means the tension is already too high.


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## Big Red Bianchi (Sep 11, 2009)

*Solution*

Well, I took the bike to a mechanic who does top end work. He's incredibly meticulous, and I knew if anyone could figure this out, he could.

He tightened the tension on the front DR cable and the problem went away.

The other two bike shops are now dead to me.

Actually, he spent about two hours with the bike. He replaced the bar tape, cables, cable housing, cleaned/lubed/adjusted the entire bike. Buffed the brake pads just slightly. Adjusted the brakes, cables, dr's, etc.

He also installed my new K-Edge chain catcher, which I don't think I really need, now that the bike is adjusted PERFECTLY. (But it's nice to have.)

The guy's a genius when it comes to working on my bike.

Total cost:  $30 for parts, and a box of donuts.

I took the bike out for rides yesterday and today and it has never shifted better.

I tried all KINDS of crazy cross-chain, weird chain combinations/changes/whatever. No matter WHAT I did, the chain just effortlessly and silently moved from one ring to the other, one cog to the other.... Not once did it even touch the chain catcher.

Life is bueno

-Bianchi Bob


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## wim (Feb 28, 2005)

Big Red Bianchi said:


> He tightened the tension on the front DR cable and the problem went away.


Peculiar way to fix that problem. But perhaps he's not telling you what else he had to do to make the problem go away. Whatever, glad you're ready to ride again


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## cxwrench (Nov 9, 2004)

Big Red Bianchi said:


> Well, I took the bike to a mechanic who does top end work. He's incredibly meticulous, and I knew if anyone could figure this out, he could.
> 
> He tightened the tension on the front DR cable and the problem went away.
> 
> ...


there is a good reason that every pro race bike has some type of chain catcher installed...and it's not the chance of having a derailleur that isn't adjusted perfectly.


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## Big Red Bianchi (Sep 11, 2009)

wim said:


> Peculiar way to fix that problem. But perhaps he's not telling you what else he had to do to make the problem go away. Whatever, glad you're ready to ride again


Here's what happened:

I walked into the shop and told him what was happening.

He put the bike on the stand and I showed him how the chain was throwing too far to the left/inside. This was clearly causing it to fall off the small ring and onto the top of the dog tooth.

He adjusted the cable (barrel?) to tighten the cable.

The chain shifted cleanly and did not fall over the small ring onto the dog tooth but rather moved off the big ring, neatly onto the small ring.

Then I left for a couple hours and he did all the rest of the work.....


-Bianchi Bob


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## cxwrench (Nov 9, 2004)

so the derailleur was moving too far to the inside and he fixed it by adjusting cable tension, not by limiting the derailleur travel?


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## Sprokets (Mar 6, 2012)

Awesome tips! Tnx.


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## wim (Feb 28, 2005)

Sprokets said:


> Awesome tips! Tnx.


Yes, except the mechanic's one about "adjusting the cable barrel to tighten the cable." If that indeed fixed the problem, it might not stay fixed for long.


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## cxwrench (Nov 9, 2004)

wim said:


> Yes, except the mechanic's one about "adjusting the cable barrel to tighten the cable." If that indeed fixed the problem, it might not stay fixed for long.


wim, i have a feeling someone was trying to up their post-count w/ that one 
i totally agree w/ the comment about the 'amazing' mechanics diagnosis and 'fix' for the OP's problem. i wonder if he actually works at a shop...although considering the stuff that comes in to our shop all the time, it wouldn't surprise me.


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## wim (Feb 28, 2005)

cxwrench said:


> wim, i have a feeling someone was trying to up their post-count w/ that one


Yea, I need to get informed on "post-count" and "rep" and all that good stuff. The internet came into my life when I was already approaching dotage, so it's a bit daunting sometimes.


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