Jim’s Tech Talk
By Jim Langley
One of the “new” trends in cycling is the 1X (say “one-by”) drivetrain. On these there is only a single (one) chainring. This makes for easy, uncomplicated shifting. Need a lower, easier gear to fight a headwind or top a climb?
No problem. Each shift onto each larger cassette cog on the rear wheel makes the pedaling a little easier. To get the easiest pedaling gear, the lowest one, shift all the way to the top/largest cog.
And to shift into harder gears, 1X drivetrains are shifted in the opposite direction – from the larger cogs down to the smaller ones. The smallest cog is the highest gear, perfect for when you’re flying downhill or enjoying a ripping tailwind. So, basically, all 1X riders do is shift one lever back and forth to access the entire gear range.
This is especially attractive to anyone who has never ridden a multi-speed road bicycle before. Because now, any gear fear of having to learn how to operate two levers and actually find the “right” gear, is tossed out the window. Shifting a 1X is a no-brainer, which is one of the reasons road bikes with them have caught on.
One Minor Drawback
While, if you’re lucky, you might never experience it, there is one issue with 1X drivetrains to be aware of. It’s chain drop, the possibility of the chain falling off the single chainring on rides.
The chain can also drop on 2X and 3X (double and triple) drivetrains. But, with these drivetrains, it’s usually possible to shift the chain back on rather than having to stop and lift the chain back on (what’s required with 1Xs). Because 2X and 3X drivetrains have front derailleurs that act as chain keepers.
Chain Retention Features
Most modern 1X drivetrains have features built into the chainring to help keep the chain on. Some have taller teeth, others have wavy teeth or alternating thick/thin teeth to cradle and keep the chain in place.
Similarly, some brands and types of chains are directional and designed to only work when installed a specific way.
Chain Drop Solutions
1: Check that your chain is installed correctly on the bicycle and on the chainring, too. Checking the instructions that came with the chain (you can find them online, too) will explain how to tell if it has a direction and if so, what to look for to make sure it’s on right. For the chainring, look for chain alignment directions stamped into the ring near the teeth. It should be self-explanatory.
2: If the chain suddenly start falling off, a likely cause is a worn-out chain. Since the chainrings need to have a good grip on the links, when they’re too loose from wear and tear, the ring can’t hang on as well and the chain can fly off. So, with any 1X drivetrain, it’s a good idea to check chains for wear frequently with a good tool, such as Park Tool’s CC-2 Chain Checker ($27.95) , which has a wear gauge on it making it easy to monitor your chain’s condition over time. A worn out chain should be replaced.
3: Like the worn chain, a chainring can be worn out, too, and that’ll let the chain drop. It’s hard to see chainring wear, but you can tell if the chain links fit loosely on the teeth and the teeth become hooked. You can also keep track of your mileage and riding conditions and learn through experience how soon you wear out 1X rings. You might even want to keep a spare on hand.
4: A bent chainring can throw chains. It’s easier to see a bend in a ring after lifting off the chain. Just turn the crank by hand slowly as you look down at the ring from above. If it’s wobbly enough to throw the chain every now and then, you’ll be able to see it. It takes a little care, but it’s not that hard to straighten bent rings. It can be done with an adjustable wrench with the jaws set to just slip over the ring. You can then hold the handle and gently pull/push on the ring at the wobble to get it straight again. If you start gently and work little by little never trying to bend it too far at one time, you should be able to straighten it enough that the chain stays on.
5: Most newer 1X drivetrains come with rear derailleurs with clutches in them. The clutch is a device that prevents the derailleur cage that holds the chain from swinging excessively over bumps. This helps keep the chain on. So, if you have a 1X bike that does not have a clutch rear derailleur, upgrading the rear derailleur to a clutch one can fix the problem.
6: A loose bottom bracket can cause the chain to come off occasionally. The bottom bracket is the bearing mechanism inside the bicycle frame that the crankset spins on. If the bearings or cups become loose, it allows the crankset to rock side to side a little. This rocking is amplified at the chainring and if the chainring rocks enough, the chain can derail and fall off. You can feel for BB play by holding both crankarms and pushing and pulling sideways. There should be zero side-to-side play. To remove the play could be a simple adjustment or you might need a new BB, which isn’t usually all that expensive.
7: On some 1X bicycles there’s another fix for chain dropping. It’s adding a chain retention device called a chain keeper. These attach to the frame and have a small cage that encircles the chain and keeps it in place on the ring. If anything begins to dislodge the chain and cause it to drop, the links instead bump into the sides of the chain keeper and it pushes the chain back onto the ring so it can’t come off.
If you ever have chain drop on your 1X I hope these tips help you fix it for good.
Ride total: 9,389
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.