Chain Wrapping Up On Itself When Changing To The Smallest Chainring: Any Ideas?

Lovacott

Senior Member
This has never happened to me before, but on the way home on Monday night, my drivetrain seized solid as I changed down to the smallest chainring on the way up a very steep incline (I changed down whilst I had good momentum so I wasn't loading the drivetrain).

I walked the bike the rest of the way up the hill and popped the chain back onto the middle ring and completed my journey.

When I got in, I suspended the rear wheel and went though every gear combination trying to figure out what had happened.

The only gear combo which gave a hitch was small front to small rear which caused the chain to wrap around and back up the front chainring until it jammed against the section of chain feeding into the top of the chainring.

I've tried everything this week to put it right.

I've re-indexed both the front and back from scratch, thoroughly cleaned and oiled everything, checked the chain for deformities, checked the alignment of everything.

What puzzles me is that I have never had this problem before, I had ridden without incident for the ten miles into work and most of the way home, but then this suddenly happened?

Over the last four days I have put quite a few hours into this and last night, I thought I'd cracked it. But, lo and behold, the same thing happened tonight on the way home.

One thing I have noted is that when the chain is on both of the small rings, there is a noticeable sag in the chain and I wondered if maybe my rear mech is not providing enough tension to the chain, therefore allowing it enough slack to ride up the front chainring?

Any thoughts would be welcome.
 
Last edited:

Gunk

Veteran
Location
Oxford
Sounds like the chain could be too long, have you recently changed it?
 
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roley poley

Senior Member
Location
leeds
You are running a triple. Small to small will always be a problem. Effective chain length is too long so you are getting chain suck.
You shouldn't be in that gear - ever. And certainly not going uphill.
Sorry, but your technique is wrong.
was told big to big or small to small caused too much chain deflection and friction but am willing to be corrected by my elders
 

Darius_Jedburgh

Über Member
Not having seen the bike I'm guessing a bit, but my suspicion is that small to small means there is more slack in the chain than the rear mech can tension. So the chain is running slack, same as if it is too long, so chain suck occurs.
You can get away with small to small on a double, but not with a triple. Anyway, there is no need to be in that gear. That ratio is available elsewhere in the settings and shouldn't give any problems. As I said - technique is wrong.
 
OP
Lovacott

Lovacott

Senior Member
You are running a triple. Small to small will always be a problem. Effective chain length is too long so you are getting chain suck.
You shouldn't be in that gear - ever. And certainly not going uphill.
Sorry, but your technique is wrong.
I use that combo on a couple of sections because it works well for me (I've tried every permutation of gears but small to small works best for me on those sections).

I've never had the "chain suck" problem before Monday this week (after more than 2,500 miles of commuting).

The chain is only three weeks old, the freewheel is also only three weeks old. The crank set is four months old.

The chain and freewheel are like for like replacements for what was there before (make and model).
 
OP
Lovacott

Lovacott

Senior Member
Not having seen the bike I'm guessing a bit, but my suspicion is that small to small means there is more slack in the chain than the rear mech can tension. So the chain is running slack, same as if it is too long, so chain suck occurs.
You can get away with small to small on a double, but not with a triple. Anyway, there is no need to be in that gear. That ratio is available elsewhere in the settings and shouldn't give any problems. As I said - technique is wrong.
There are a couple of 25% inclines on my route which turn into mega slopes near the peak and I find it better to change down on the front when there is not too much load on the drivetrain. If I leave it late, I have too much loading and the front won't shift down.

So I shift to the smallest on the front as I start the incline and then work my way down at the back as the hill gets steeper.

Like I said in the OP, I've never had this problem before so I am looking for possible causes.
 
OP
Lovacott

Lovacott

Senior Member
Is this what you meant?

View attachment 569105

It's called chain suck.

I have only experienced a minor case of chain suck - and it was remedied by cleaning the chainset - try this page for a fuller explanation and solutions.
https://www.mtbr.com/threads/workbench-how-to-un-suck-your-chainsuck.1169608/
Not a perfect solution, but the cable tie idea in the article works a treat. I've just tried and tested it.

It limits the "suck" to the height of the chain stay and prevents the chain wrapping in on itself.

Worth doing as a safety measure at least.
 
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