Preventing dropped chains: No ’cross drivetrain is foolproof

Days spent stretching, prepping, and gluing tubulars. More time each week washing and tuning bikes than actually training on them. Seeking, always seeking, that perfect, mechanical-free race. Then, on race day, the chain drops. Seconds and places flood past.

You’re not alone.

Sven Nys dropped his chain at the Milton Keynes World Cup, and based on how he rode the rest of the race, from last to eighth place, it may have cost him the win.

Cyclocross is unique, taking road equipment off-road in some of the worst conditions of any discipline. You pick up the bike, set it down, and ride it through bumpier sections than even the most blown-out downtown criterium. At the equipment level, cyclocross is akin to the cobbled classics. Prepare for the worst, and pray for the best. But unlike the cobbled classics, the cyclocross calendar lasts four months. The hairiest classics last for only 10 days in the spring.

Chain retention is a big problem made up of smaller problems. Address each of these and you have a solution — or at least a fighting chance.

Problem one: All chain watchers are not equal

In recent years, the chain watcher market has exploded. Since K-Edge launched its first chain watcher on the bike of Kristin Armstrong for the Beijing Olympic time trial, other brands have scrambled to imitate the K-Edge design.

That design, the Road Braze-On Chain Watcher, works great on the road but is not worthy of a cyclocross bike. It can flex under extreme loads, like that of a ’cross rider accelerating out of bumpy corner, and if said rider’s chain happened to bounce just off the inside of the small chainring, that acceleration can force the chain past the chain watcher and trap it in a bottom bracket prison, where the chain watcher goes all Benedict Arnold and acts as the guard to keep your chain derailed.

SRAM, Rotor, and Origin8 all designed chain watchers that are an imitation of K-Edge’s Road design. It’s not a poor design, but as the name of the K-Edge watcher says, they are for road use. You’d often be better off with no chain watcher at all than any watcher of this design.

Other potentially problematic chain watchers for ’cross riders are integrated into the frame. Nys rides a Trek Boone 9 with Shimano Dura-Ace Di2, which we featured in a gallery in September. The Boone has an integrated chain watcher, which is adjustable and removable with a single Allen bolt.

When not set up just right, the Boone’s chain watcher can be a dark abyss for jammed chains, which, according to Trek’s Matt Shriver, is what happened to Nys on Saturday. “Sven and another rider collided causing a miss-shift. When he jumped back on [the bike] it had shifted to the small ring. He went to pedal and lost his chain to the inside.”

The cause of the incident and subsequent time loss was three-fold: the collision with the other rider, the sensitivity of Shimano’s Di2 shifters, and the Boone’s chain watcher not being close enough or stiff enough to hold the chain on top of the small chainring when Sven tried to get it back on. The result was Nys chasing back from nearly last place.

There is an answer for the double-chainring cyclocross rider, like Nys, and it lies in K-Edge’s Cross Double XL chain catcher. Frankly, it is overbuilt and expensive, but in my time of using it with multiple bikes and drivetrains, it has never once let me down. It can be used on round seat tubes, as well as braze-on only frames, such as the Specialized Crux and Ridley X-Night. Additionally, K-Edge makes a Cross Single XL chain catcher for the single-ring crowd, but more on that later.

Problem two: Your chain needs insurance and a backup plan

While most pros riding a single-ring drivetrain are doing so without a chain watcher of any kind, that approach is not foolproof. For the average rider, those of us who will likely take a spill or two on a muddy day, a little extra money and weight spent around the crank will pay dividends.

A double-ring drivetrain already has an insurance policy: the front derailleur. The K-Edge Cross Double XL should be your backup plan. Remember, you need both. When both are in tune and set up properly, you have an impenetrable crankset.

So why abandon such a setup in favor of a single-ring?

SRAM’s CX1 drivetrain is good, but not great. It has its shortcomings, which we found while testing the Focus Mares CX 1.0 for this year’s cyclocross bike shootout. During a local short track race, our tester, seasoned elite rider and web editor Spencer Powlison, took a bumpy turn at speed and the chain derailed to the outside of the CX1 chainring while exiting the turn. We have heard of similar incidents, and at the first stop of the Bpost Bank Troffee I watched Telenet Fidea rider Thijs Van Amerongen dismount his bike and put his chain back on the ring after rounding a fast corner.

SRAM makes no claims that its CX1 system will never drop a chain, though a high-level of security is implied in its marketing. Hardly any riders are using any sort of chain watcher — so they have no insurance (derailleur) or backup plan (chain watcher).

Thanks to the narrow/wide chainring and roller clutch rear derailleur, dropped chains with SRAM’s 1x systems are sporadic. But for most racers, some sort of reassurance is needed for a foolproof system.

There are two approaches to insuring your single-ring drivetrain. The first is running a single-ring specific chain watcher. Mountain bike brand MRP offers its 1x chain watcher, but its compatibility is limited as it will only work on bikes with round seat tubes.

The answer for riders with braze-on front derailleur mounts comes in another K-Edge chain watcher, made specifically for SRAM’s CX1.

Sadly, this product is not yet on the market, though it has already earned multiple UCI wins under Danny Summerhill (K-Edge-Felt). The K-Edge chain watcher will be compatible with round seat tubes as well as braze-on front derailleurs and like all K-Edge products, is CNC’d out of aluminum in the USA. Availability date and pricing have yet to be determined.

The second option to insuring your single-ring drivetrain is to not buy a SRAM CX1 chainring, which limits the user to a single ring. Other narrow-wide tooth options on the market, such as those from Absolute Black and Wolf Tooth Components, can be installed with an outer ring guard. The SRAM CX1 chainring is partially brilliant because of the way it mounts to the outside of the crank and is offset toward the seat tube so that the teeth sit in the center of the chainline. Unfortunately, that means you cannot mount an outer chainring guard.

The outer bash ring keeps the chain from flopping to the outside, while a K-Edge Cross Single XL or similar chain watcher tends to the chain on the inside of the crank. K-Edge’s Cross Single chain watchers sport a machined tooth that hangs over the chainring, to keep the chain from bouncing up, and the burly design makes dropping a chain to the inside as close to impossible as we’ve seen.

The bottom line

For those of us not chasing UCI points, equipment is often recycled from our road bikes at the end of the season and repurposed for cyclocross. Pretending that the majority of the market will walk into their local shop and purchase two “cyclocross” drivetrains is folly. This is part of what I liked about SRAM CX1 — the Force CX1 rear derailleur could be used with any 10- or 11-speed SRAM shifters, meaning that all a rider needs is a new chainring, chain watcher, outer ring guard, and a chain.

In the real world, having a properly tuned bike is the largest factor to having an issue-free race. Though, as Nys showed us, having one of finest tuned bikes in the world does not mean it is chain-drop-proof. The solution that is best for you depends on your bike. It also depends on you, and whether you’re ready to make the jump to a single chainring.

A little extra weight is better than standing on the side of the course putting your chain back on by hand. Having multiple lines of defense against the dropped chain offers peace of mind, and perhaps a few places as well.