GRedner

In accordance with Murphy's Law, I had my first encounter with the phenomenon of "chain suck" at the farthest point on my ride today. Fortunately it happened at extremely low speed (I was making a U-turn on a two-lane road).

I was pedalling slowly around, and suddenly the pedals locked and refused to turn forward. I immediately stopped and got off the bike, and I saw that the chain had not disengaged from the chainring, the part of the chain that was supposed to be leaving the chainring was folded up under the part that was arriving, and the jockey wheels of the rear derailleur were pulled as far forward as they could go.

I turned the pedals backwards about 1/4 turn, and the chain disengaged and everything snapped back into place. There was no visible damage to the chain or drivetrain. I rode home, and everything seemed OK.

Are there steps I should take to avoid the possibility of this happening again, at higher speed?

MudPie

Chain suck, well basically sucks. You might want to check the teeth on the chainring from which it sucked. Often, a tooth could be bent and not allowing the chain to release.

Chain suck can be caused by many events, such as "improper" shifting, dirty/unlubed chain, or just the overall design of the bike (clearance between chain stay and chainring).

Sheldon Brown makes a reference to the following site: https://fagan.co.za/Bikes/Csuck/

Retro Grouch 

Check the teeth on your granny gear for any sign of burrs on the sides of the teeth. The burr catches the chain and can pull slack the bottom chain run up on the back side. The cheap fix is to wire wheel the chainring to remove the burrs. The better fix is to replace the chainring. I prefer stainless steel granny rings because they wear much more slowly and, consequently, are much less subject to chain suck.

GRedner

Well, here's the weird part - the suck happened on the middle chainring, and try as I might I can't see any burrs, aberrations or damage on it. The chain has about 400 miles on it, and the chainrings and cassette a couple thousand. The chain was just cleaned and re-lubed, and both derailleurs re-adjusted.

MudPie

What brand bike/chain/crankset do you have? I have a Gary Fisher Cake 2DLX and those are notorious for chainsuck. I've read many reviews and many have complained about chainsuck. However, I am not using the stock Shimano chain, rather I've replaced it with a SRAM from day one. I "only" had one or two chain suck events in the past 2.5 years. Not a bad rate, as mountain bikers tend to suck chain more frequently than roadies, since we tend to panic shift and often shift under load while bouncing through a rut. I assume you have a road bike.

A friend had an early Fisher mountain bike and his came with a "anti-suck" device, a bolt on piece of hardware that prevented the chain from getting between the chain ring and chain stay. He said it really worked and did ride without it only to get chain suck. I surmise someFisher designs are more prone to chain suck.

Another reason for chain suck could be a statistcally improbable condition of one bad link and one bad tooth with just the right pedaling force. The mating of that particular tooth and link might be a potential chainsuck condition, and to add another variable, it may suck only if that tooth and link mate as well as how hard you're pedaling. I assume one can calculate how often a link will mate with that one tooth.

Al.canoe

True chain suck as opposed to the chain just jumping off a ring, is due to too much force on the pedals when downshifting. The solution then, is to ease up more when you shift to a smaller ring.

Al

GRedner

It's LeMond road bike. I don't know offhand who makes th casette and chainrings - they're the original ones that came with the bike. The chain is an SRAM 9-speed.

This particular chain had a stiff link in it that I'm pretty sure I completely freed up - perhaps it's not as 'fixed' as I thought. Either way I'm going out for another ride this evening, hopefully with no suckage!

GRedner

When it happened I wasn't shifting, and was barely applying any force to the pedals at all. I was leaned over pretty sharply to the left, though - I wonder if the chain shifted to the side and got caught?

mlts22 

When I saw this post, I first thought "my chain sucked", as in it wasn't well made, rather than an occurance of chainsuck... and was going to maybe mention a Shimano chain + master link, or a SRAM chain (which includes a master link for chain removal easier than yanking out a chain breaker) as a possible alternative.