(SPEC’S) 12/25, Cassette - Compact chainring - I just replaced the chain and I'm getting what I think is chain suck while shifting to the small front chainring.


1st question,
Could my chain be too short if I can shift up to the large cog on the cassette and the large chainring in the front?

2nd question:
And can a short chain cause chain suck?


Thanks,
Marty
PS, it's my suspicion it's the front big chainring, just narrowing.

A short chain doesn't cause chain suck . What does cause chain suck is a front derailleur being out of adjustment . As far as your chain being too short ,you need to show a photo of your drive train . More so of the rear derailleur . I am not there to see what you have . Being in large chain ring and the largest cassette gear is cross cogging which is a bad thing for your gears and chain .

or on rough off-road tracks it just happens .. a stair step fence under the chainstay was a good add-on

to fill the gap so there was no place for the chain to Go to get sucked up into ..

Never heard of it, is this mountain bike specific? My question is about road bike.

I will supply a photo. What gears do you want to see the chain positioned on the drive train/rear derailleur ? Thanks!

they were the ones riding on rough ground.

I rarely have chainsuck, on my road bike I have a N-gear jump stop that keeps the chain on the inside chainring on the top.

when overshifting to the inside (I ride triples on my derailleur bikes )

K edge makes one that the bolt that holds a Braze on FD on holds it on as well.

N-Gear, Home of the Jump Stop ... Chain Catchers for Road, Cross, and MTB Bikes - K-EDGE

the small ,small combo will be fine . that way I can tell if it too short .

Ok will upload in about an hour when I get home from work. Here's a pic with a rudimentary explanation.

It dropping off the chainring at the derailleur like it should. It’s getting hung up on the last 2 teeth on the chainring, see pic. (I added the yellow arrows). So what it does is stick right there on the teeth and it then comes back up the ring and slams into the derailleur.

check to see if the chain ring(s) is /are bent . if so they can be bent back with a adjustable wrench . make also sure the rings are tight to the spider and the arms are to the bottom becket . if any of this is gong on then yes it could be your problem .

That makes me suspect a worn chainring.
I've worn out two chainrings that way, and it always happens with a new chain.
The teeth of the chainring get slightly hooked, so instead of the chain smoothly coming off the bottom of the chainring to go to the RD, the teeth hold onto the chain and pull it up into the bottom of the FD.

you can always file down any burrs or hooks on the teeth so the chain doesn't get catch on them .

Crank tight, will check chain ring to spider arms, and also will check the teeth for any being bent,,, thanks!!

- Yes this is what lead me to either my chain being to short (I cut and installed) or the large chain ring is worn.

I will post a picture here in a little while showing at least a straight on shot of the chain ring..they look really warn to me. (I bought the bike recently and now I'm working with this issue).

Thanks for the help guys!!!

detail needed about ALL drivetrain components, you cannot omit anything. Any mismatched components, may they be chains, cassettes, cranksets or anything else can contribute to minor issues. I use a Campagnolo equipped bike, but I have been using KMC chains. Campagnolo claims that using KMC chains can result in chain suck in some conditions. Know what? they are right. Sometimes my bike that has a KMC chain experiences chain suck. My other bike with a Campy chain doesn't. When you ask a question, ALL details are important

Nope. Derailer adjustment has nothing to do with chain suck. Chain suck happens when the chain remains connected to the teeth and pulls the chain upward instead of chain being released at the bottom of the ring. This is due to a bent tooth or a burr on the tooth. The teeth on the ring can be bent back (maybe and very gently) or the burr can be filed off.

Huh, I always use small-small to see if the chain is too long and the large-large to see if it is too short...

Component Group Shimano 105
Chain length pics





Front shot of derailleur position



Chain rig teeth pics







Anything else I need to supply information wise??

Suggested possibilities from you guys:
1. Bent tooth and or burrs on the teeth. - Straighten and or file teeth
2. Worn chainring – Replace
3. Front derailleur out of adjustment. Not sure thing would cause chain suck but I supplied a pic of at least a picture of the derailleur. (Straight on shot). Side picture showing alignment vertically was impossible for me to get.
4. Loose, spider and the arms bolts.

So after zooming in on the teeth what your thoughts, bad or ok?? I know that’s hard to say but maybe pictures help a little.

Thanks a bunch guys!

That crankset has pretty much zero wear,shouldn't be a problem. One thing I notice is that the front derailleur looks as if it is set too low, could be the angle the pictures are taken from, or not. Worth checking out in any case. Thanks very much for all the additional information,very helpful.

"Zero wear", wow I was looking at the differences in the flat spot on the large ring compared to the small and thought is was toast. Large ring looks pointed compared to small. I guess I will look for burrs or bent teeth next.

Also if a link is stiff on the new chain. (BTW is this new chain which is for a "Ultegra CN-6701"group set and not a shimano 105 chain ok??



- Thanks for the tip on the front derailleur.

For the correct chain length check this Shimano document: https://si.shimano.com/php/download.p...001-13-ENG.pdf
Scroll down to page 16, section 3 <When largest sprocket is 27T or smaller>
There are also tips on aligning the front derailleur.

A stiff link would cause a jump each time it reaches a certain point in the cycle. If you have a stiff link then you may need to tweak the link with a chain tool until it moves freely.

Your chainrings aren't worn. The front derailer can't cause "chain suck". Your problem is likely due to a burr which we can't see in your picture. Burrs can happen on the first ride or the second or the 100th or... Most of the time they are caused by a bad shift. If you've ever shifted and your chain clatters rather then lifts up on the ring, that's when a burr can form. Just the action of the chain moving from on ring to another on a upshift can cause the problem.

As the chain lifts up onto or off of the rings, it can gouge an aluminum ring and leave a small raised bit of metal. Since 10 speed chains are very narrow, there isn't a lot of room and even a very small burr could cause the chain to stick on a tooth. Shift the chain off the ring and inspect each tooth for any kind of scrape marks or raised bit of aluminum. You may have to look very closely as the burr can be small.

Don't be fooled by teeth with different profiles. That's not a worn tooth but a design feature. The flatter top on some teeth is going to occur around the lift pin (it that little rivet in your last picture) and they aid in shifting. They make the shifts quicker and smoother.

Personally, I wouldn't say your derailer is low. It should have 2 to 3 mm of clearance over the teeth. That's about the thickness of a nickel. It doesn't look like you are far from that in your picture.

I really wanted to know what the correct chain length spec is so thanks a bunch!

Thanks for the verification concerning the chainring wear concern, I'm good there. Now I will check for burrs or bent teeth tonight. Also going to check the chain for a stiff link pin. I'm getting this thing narrowed down!!!

Ok. - This is good info to know, thanks!


Thanks