Jim’s Tech Talk
By Jim Langley
A chain keeper, also called a chain catcher is a device added to bicycles with double-chainring derailleur drivetrains to prevent the chain from falling off. Chain keepers can be mounted to the front derailleur as with the popular K Edge model shown in the package here. Or as you’ll see in the photo here of my gravel bike, it can be mounted to the frame. Notice how close the chain keeper’s tip/tooth is to the chain.
Two Examples of Chain Keepers
What Chain Keepers Do
Chain keepers work by blocking the chain if it tries to come off the small chainring and fall to the inside. This is a great thing because if a chain comes off that way it’s possible for it to get jammed in-between the crankset and the frame. If a chain gets jammed down there it can be difficult and time consuming to extract it.
Worse, if you don’t realize what’s happening and continue pedaling it’s actually possible for the chain itself to bend or for the chain to gouge and damage your frame. If it’s a thin-wall metal frame this might dent it. If it’s carbon it could damage the carbon.
Note that for single-chainring (called 1X, say “one by”) bikes there are also chain guides, which are different from chain keepers/catchers. Because they cover the top of the chain and both sides. That’s because with a single chainring the chain may fall off to the inside and to the outside.
Why Did Chain Keepers Become a Thing
In this article we’re focusing on chain keepers/catchers on double-chainring setups. In days of old (up until about 2000) you didn’t need chain keepers because the front derailleur did the job of keeping the chain from falling off. And even today on modern 11-, 12- or even 13-speed drivetrains you might never drop a chain thanks to the front derailleur.
However, chain keepers have become more and more popular as road drivetrains have widened from 120mm to now as wide as 142mm. That extra width means a greater chain angle, which in turn means more likelihood of a chain coming off.
TIP: If your front derailleur keeps the chain on nicely, it will probably also shift it back on in the rare event the chain falls off. To do it, just pedal gently (no real force on the pedals) and operate the front derailleur gently as if you’re shifting from the small to large chainring. With any luck you will pedal the chain back onto the small chainring and never even have to get off your bike.
More a Problem for Racing and Hard Competitive Riding
Chains don’t usually fall off if you’re just riding along. Most of the time it happens from a shift under pressure or a bad bump while changing gears or especially from crashing. Chains are more likely to come off if you pedal backwards too.
Racers have the most dropped chains because they have to shift to get in the exact gear not to get dropped or to try to launch the winning sprint. If that gear change happens under massive pedaling pressure, it’s asking a lot of the entire drivetrain and sometimes things go wrong.
Even with Keepers Chains Come Off
Those two reasons are why chain keepers are on more and more bikes. The one on my new gravel bike shown above came installed on the bike.
But the key thing everyone with a chain keeper on their bike needs to know is that the chain may still fall off. The same things that make the chain come off without a chain keeper can throw it off with one.
Chain “Keepers” also Keep the Chain Off!
And if the chain comes off, guess what? The chain keeper will then keep you from being able to shift the chain back on with your front derailleur. And it will also make it very difficult to impossible to put the chain back on by hand. You won’t be able to do it unless the keeper is very loosely adjusted, which in most cases it won’t be.
Carry the Right Tool So That You Can Get the Chain Back On
This means that you could get stuck by the side of the road because you cannot put the chain back on. So if you have a chain keeper, I recommend that you carry the right tool to be able to move the chain keeper out of the way of the chain so you can put the chain back on by hand.
For the two keepers in my photos, all you need to carry along is the right allen wrench to loosen one bolt and you can then swivel the keeper a little further away from the chainring, lift the chain back on and then put the keeper back where it was and tighten the screw. That’s all there is to it. But you can’t do it without the right tool. So be sure to carry it.
Possible New Product Idea?
If you know of a chain keeper that can be opened and closed without tools please share it because that would be an excellent feature. I haven’t seen one. Maybe it’s an opportunity for a new product inventors!
Jim Langley is RBR’s Technical Editor. A pro mechanic & cycling writer for more than 40 years, he’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Tune in to Jim’s popular YouTube channel for wheel building & bike repair how-to’s. Jim’s also known for his cycling streak that ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.