Chainsuck, its cause, and how to prevent it in the first place
Worn chainrings and a grimy chain is a recipe for chainsuck—a condition that can not only ruin your ride, but your bike as well.
Whomever coined the word “chainsuck” deserves a pat on the back. Not only is the phrase quite descriptive, it sounds appropriately miserable—it can halt your ride in an instant and, in extreme cases, cause costly damage to your frame and componentry.
Just what is chainsuck?
Chainsuck happens when the bicycle chain fails to disengage from the teeth of a chainring—usually during a shift—and wraps back up and around the chainring. Here’s a classic visual:
Chainsuck usually occurs during a shift when the chain does not disengage completely from the ring it is shifting from. It can occur down-shifting from a bigger ring to a smaller one, or when up-shifting from a smaller ring to a larger one. If conditions are just wrong, it can also happen simply when pedaling.
Sometimes the suck is so bad, as illustrated in the image above, that the chain wraps and travels up into the front derailleur a second time. Other times it’s just temporary and the chain pops off as it comes up and contacts the chain stay. Though you can feel this pop and it usually does no damage, you should take notice and solve the problem before the chainsuck worsens and becomes expensive. A bad incidence of chainsuck can do significant damage, from scraping paint off the chainstay to causing structural damage. It can also bend or break the front derailleur cage.
What chainsuck is not
We’ll address some common causes and techniques to prevent this malady, but first let’s talk about what chainsuck is not. The term “chainsuck” is commonly misused to describe all sorts of chain related problems.
The chain falling off the front chainring is a bummer for sure, but not chainsuck. The chain getting jammed between the small ring and the bottom bracket shell is super annoying but not chainsuck. The chain getting stuck between a tire and the chainstay, well, that totally sucks, but it’s not chainsuck either.
The first two issues are likely overshifting caused by a maladjusted front derailleur. The latter is usually the result of freehub drag. All subjects worthy of another conversation, but for now we’ll stick to actual chainsuck and how to remedy it.
The causes of chainsuck
“Chainsuck occurs primarily when downshifting under load from the middle to the smallest chainring,” wrote the late bike repair guru Sheldon Brown. “The bottom run of the chain may not immediately disengage from the middle ring, and can get carried upward until it wedges betwixt the chainwheels and the right chainstay. This jams the crankset.”
Brown discusses this in context of the “middle to the smallest chainring,” but it can actually occur between any two rings. That said, it seems more common for 1) smaller chainrings because of the tightness of the radius; and 2) for chainring sets with a big difference in size, because of the tight chain transition needed to make a shift.
Brown also denotes chainsuck as occurring “when downshifting under load”—and he’s right about that being a primary cause. It takes energy to bind the chain onto the teeth, which comes from pedal pressure.
Below is a list of contributing causes. Not all have to be present for chainsuck to occur, but often it’s one or more of these circumstances that causes the problem. These factors are listed in a generalized order of importance:
Chainsuck contributors and solutions
1. Shifting under load—particularly down-shifting
Shifting while pedaling hard puts added stress on the chain and chainrings. It forces the chain to bend tighter than normal, and pulls the chain tightly between the teeth as it’s trying to transition away from those teeth. Down-shifting under load has the greatest tendency to bind the chain onto the teeth. When high pressures are applied while it tries to release, the chain can be pulled too tightly on the teeth. Normally, a chain will not bend that tight, but if forced, it can twist and “stick” to the teeth.
Solution: Don’t shift under a heavy pedaling load. Soft pedal just as the shift occurs, then resume the hammering. Rings with technology like WickWerks increase the speed of the shift so the amount of soft pedaling is reduced.
2. Damaged chainring teeth or chain
Damaged drivetrain parts can also be a big contributor to chainsuck. If a chainring tooth gets bent or mashed just a little, it can act as a hook, keeping the chain on the tooth—or more problematically—acting as a broad point where the chain can bind. A bent or twisted chain link can also cause a similar problem.
Solution: If you damage a chainring, repair it with pliers or file, or replace it. If you damage a chain, replace it. Chains are relatively cheap and easy to change so when in doubt, replace it. With damaged components you usually have some warning signs—a ticking, weird noises, a thumping in the pedaling, or shifts that don’t feel right. Don’t ignore these signs. Get things fixed before they end up costing you even more money.
3. A dirty (especially gritty) chain:
It can be a blast to ride in dirty and muddy conditions, however, grit and dirt in and around the links of a chain can significantly contribute to chainsuck. It’s theorized that dirt particles close the narrow space between the teeth and the chain links to create a binding effect when shifting. Many chainrings that shift perfectly under normal conditions can chainsuck when ridden in the mud.
Solution: Proper lubricants for the conditions—in the above described case, a wet conditions lube—helps this problem considerably. But even more importantly, adjust your shifting technique so there is little pressure during the shift. It takes energy to bind the links onto the chainring teeth, so removing that factor greatly reduces the possibility of chainsuck.
4. A very dry chain (needing lubrication):
The story on dry chains is similar to that of muddy conditions. When the chain is particularly dry or lacking lube, especially when conditions are really dusty, chainsuck is more common.
Solution: Again, proper lubrication—a dry condition lube—helps this problem considerably. And, like above, so does adjusting your shift technique to reduce the load on the drivetrain.
5. Worn chainring teeth:
Worn chainrings can develop a hook shape that makes them more likely to snag and suck the chain. Worn teeth start to look like a shark’s dorsal fin, while good teeth are symmetrical with an even pitch on both sides.
Solution: Identify then replace worn parts. The potential of doing greater damage in other areas makes the cost of replacing worn parts an easy decision.
6. A worn, stretched or damaged chain:
Over time bicycle chains eventually grow longer or “stretch” from use. Not only does a stretched chain increase the odds of chainsuck, it shifts poorly and wears sprockets at an accelerated rate. Aside from being more likely to break, a damaged chain is more likely to bind to chainring teeth and cause chainsuck.
Solution: Check chain for wear and damage often and replace it when necessary.
7. Burrs on the teeth of new chainwheels, mismatched wear:
The last item is mentioned here, not so much because it’s a significant problem, but because when new rings are put with a used chain, burrs or sharp edges on the new rings can create problems. The same is true when a new chain is placed on older chainrings. Normally this results in “skipping” more than chainsuck, but it can certainly be a side issue of wear-mismatched components.
Solution: Consider replacing your chain each time you change your chainrings or cassette. Wear-matched components simply work much better and a new chain is the cheapest drivetrain element to replace.
Some closing tips and tricks
- Shift fast and with a minimal load on the drivetrain. This can’t be emphasized enough.
- Keep the drivetrain as clean as possible and lubricate the chain frequently.
- Finally, if you’re worried about chainsuck messing up your beautiful paint job or carbon chainstay, add a “peeler” to knock the chain loose if it ever tries to wrap back up and around. Zip-ties can do this pretty easily. (See the photo below.) Position them as close to the chain ring teeth as practical so that they can catch the chain before doing damage.
Editor’s note: This is an edited version of an article written by WickWerks Lead Engineer Eldon Goates.