Almost all bike riders have experienced a chain being thrown off the inside of the inner chain ring during shifting. Regardless of how well your derailleur is adjusted, or how good your shifting technique, it is almost inevitable that you will throw your chain at some point. Just ask Andy Schleck, he arguably lost the Tour de France because of this. The causes of thrown chains are varied, from a misaligned derailleur, to trying to shift into the small chain ring under high torque and at a low cadence. However, there is a way to almost completely eliminate this problem, using a device called a chain catcher. The idea is so simple that it falls under the “Why didn’t I think of that!” category.
The idea of a chain catcher is that, well, it catches your chain if it tries to come off on the inside, forcing the chain back onto the inner chain ring. Chain catchers come in two basic forms. For those of you with a traditionally-shaped (meaning round) seat tube on your bike, you can use a very basic design, like the “Dog Fang” by Deda Elementi. This is an inexpensive, plastic device that wraps around the seat tube. It has a protrusion, in the shape of a fang (hence the descriptive name!). The device is rotated so that when the chain is on the small chain ring in front and the largest sprocket in the rear, this “fang” is almost, but not quite, contacting the chain. I use a business card, folded in half, to measure this gap. The screw is then tightened, clamping the device in place, and viola! Since I put one of these on my Parlee Z2 three years ago, I have not once thrown my chain off inside.
There are also alloy chain catchers that can be used on round tubing, such as the K-Edge Clamp-On Chain Catcher, but alloy catchers are also available for non-round/”braze on” equipped seat tube designs as well. This type of catcher mounts under the bolt that attaches the front derailleur to the bike and the chain catcher hangs down behind the small chain ring. As with the Dog Fang, this extension is adjusted so that it is two business cards away from the inner chain ring when the chain is in the small ring and the largest cog in back. There are several designs available on the market, but we particularly like the K-Edge Road Chain Catcher, because of its functionality, and because of the high standard of design and manufacturing that is a hallmark of all K-Edge products. The design is available for use on road and mountain bikes.
In addition to the inconvenience of having a chain fall off, the chain coming off can actually damage your bike, and not just cosmetically, particularly if the frame is carbon fiber. The chain can scratch or gouge the carbon fiber frame in the area of the bottom bracket. Working on as many bikes as I do, I have seen this damage all too often. Some manufacturers are beginning to recognize this. For example, Guru Cycles provides a chain catcher with the Guru Photon frame, and not using a chain catcher will void the frame’s warranty. As Guru has recognized, chain catcher will provide the best protection against this damage and inconvenience.
Drivetrain manufacturers are also realizing the advantages of chain catchers as it simply makes sure that people have fewer shifting problems and that reflects positively on rider experience with their products. SRAM’s Yaw front derailleurs, introduced in the summer of 2012, come with an ingenious chain catcher incorporated into the design. While most aftermarket chain catchers mount on the bolt holding the front derailleur and thus can only be adjusted by loosening the same bolt that holds the position of the derailleur (necessitating careful readjustment of the alignment of the derailleur) the SRAM design allows for independent adjustment of the chain catcher without changing the front derailleur adjustment. Very slick. Campagnolo is also offering a chain catcher as an accessory to its EPS electronic shifting system.
Chain catchers are not perfect, however. It is possible to “beat them” if you do something seriously wrong, such as trying to shift into the small chain ring, under very high torque and/or while pedaling at a slow cadence. There is no replacement for good technique. For best shifting performance, anticipate those times when you may need to shift into the small chain ring, and do so before you need to.
My personal opinion is that any carbon fiber bicycle should be equipped with a chain catcher as protection for the frame. A chain catcher is also good idea for any bike, regardless of construction, because it protects your painted finish, and it keeps you climbing up that hill rather than standing on the side of road, frustrated and getting your hands dirty as your cycling mates ride away.
The most basic “Dog Fang” type chain catcher starts at $10.00. The alloy versions by K-Edge start at $30.00. Cheap insurance and available at Fit Werx!