Dealing With a Chain-Dropping Problem on a 1x Drivetrain

By Stan Purdum

In my recent article, “Riding Your Ebike with Cyclists on Regular Bikes,” I mentioned that I had installed a chainring from Wolf Tooth that corrected a chain-dropping problem I was experiencing on my ebike, which has only a single chainring on the crank and no derailleur. 

(In bicycle lingo, a single ring on the crank is often called a “1x” drivetrain — with 1x pronounced as “one-by.” In my case, since I have an 11-speed cassette, my drivetrain is a 1×11. My old touring bike with three chainrings and a 9-speed cassette was a 3×9. The single-speed bike I had as a kid was, technically speaking, a 1×1.)

Since several readers responded to that mention of the dropped chain problem with thoughts and suggestions, both in the comments section below the article and in direct email to me, I have decided to explain the situation further, thinking my experience may be useful to some of you should you have a similar problem. I do so with this caveat: I am not a professional bicycle mechanic; most of what I have learned has come from dealing with problems with my own bikes over the years, including breakdowns on the road and running components without realizing that their useful life was over, and by working for a few years as a volunteer in a charity bike shop refurbishing old bikes.

One other caveat: I am not writing this to drive business to Wolf Tooth, but only to explain why their chainring solved my problem.

A couple of you stated your assumption that one-by drivetrains were less likely to drop their chain than systems with two or three chainrings, and both stated that their experience with their single chainring bikes seemed to support that assumption. I don’t doubt their experience, but from what I have now learned, I suspect they are beneficiaries of recent technological advances.

Those advances came because of realities in the world of mountain biking, where 1x systems are often preferred but where the irregularities of surfaces on which mountain bikers typically ride were often causing their chains to self-derail. The bike-component industry responded with two advances: clutches on rear derailleurs that minimize the movement of the derailleur arm when not shifting and a new tooth profile on chainrings. That profile, called “narrow-wide,” features rings with a wide tooth/narrow tooth/wide tooth/narrow tooth etcetera pattern around the whole ring to match the narrow/wide plate openings between the rollers on the chains.

The best way to see this is with this video, which shows not only the wild gyrations of the chain as a bike lurches over a stony single track, but also how a derailleur clutch and a narrow-wide chainring together help to prevent chain drop, with the chain ring being the most effective of the two in an either-or situation but best prevented when both advances are present. 

My thanks to the readers who suggested the clutch to me. But in fact, I was already aware of the clutch and had it engaged on my Shimano GRX derailleur. It simply did not, by itself, prevent the chain drop. (In case you have a derailleur with a clutch, be sure to disengage it if you are removing the rear wheel, as trying to reinstall the wheel with the clutch engaged is much more difficult. The video mentioned above shows how to engage and disengage it.)

My steed is a 2021 Specialized Turbo Creo SL Comp E5 Road Ebike. To its credit, the chain drop problem did not occur when riding it with the original cassette and chain, but after replacing those due to wear over a few thousand miles, the problem presented itself. I stated in the “Riding Your Ebike with Cyclists on Regular Bikes” article that the chain dropped twice when riding with friends, but it also happened a few times while riding solo, usually when shifting rapidly. Naturally, it occurred to me that perhaps the new chain was the problem. The original was a Shimano HG601, but when replacing it, I upgraded to a higher-level chain, also from Shimano. Having no inexpensive way of testing whether that was the problem, I looked at the chainring.

That ring was a Praxis Forged/M30 Spindle Interface, and it also occurred to me that perhaps it was worn and should have been replaced with the chain and cassette, but on past bikes, chainrings have outlasted three or four chain replacements — but then my past bikes had triple chainrings, which mean the wear was distributed over the three rings and not all on one. 

But I pressed on with the original chainring, which has a narrow-wide profile, and once the chain started dropping, I found that to get the benefit of the narrow-wide teeth, one had to mount the chain so that the outer plate openings were on the wide teeth and inner plate openings on the narrow teeth. The Praxis ring even has a graphic on it to show the correct placement.

This was logical, but the problem with that is twofold: First, when on the road, it’s almost impossible to see the graphic without turning the bike upside down. The graphic is stamped on the side of the ring that faces the bike, so the only way you can see it without turning the bike over is by laying yourself flat on the ground so you can be eye level with the graphic (there’s not enough visual difference between the narrow and wide teeth to do it merely be looking at the teeth themselves). Thus, just plopping the chain on the ring without viewing the graphic means there was only a 50% chance of getting it aligned right.

Second, even when I did all that was necessary to get the chain mounted on the right teeth, the chain eventually dropped off the ring anyway.

Finally, I found a Reddit page devoted to my model ebike, where the participants discussed this problem and the primary recommendation was to swap out the original chainring for a “drop-stop” ring from Wolf Tooth, which I did, though it was not inexpensive, especially since I had to buy new bolts from Wolf Tooth since their ring did not have the threads in the bolt holes as the Praxis ring did.

Jim Langley is the professional bike mechanic who writes weekly for RBR, and for several years, he was a quality control engineer at Praxis. He tells me that the different technologies are typically protected by patents, so other companies either invent their own or pay royalties to use someone else’s in order not to get sued. SRAM invented and patented the narrow-wide chainring specifically for mountain bikes in the early 2010s, making the 1x drivetrain feasible. 

In exploring the Wolf Tooth website, I learned that “Drop-Stop” is Wolf Tooth’s patented take on the narrow-wide technology but that their version of it doesn’t require the user to figure out which chain plate openings go on which teeth. Rather they have made the wide teeth fat enough that they simply will not allow the inner plate opening to settle onto them. When installing the chain, if it will not drop into place, you just slide it to the next tooth, and the chain settles easily into proper alignment.

The Drop-Stop technology also aims to clear mud and debris from the chain — a feature especially important to mountain bikers but not unimportant to road riders. As Wolf Tooth explains its ring tooth profile, “… the wide side of the tooth has maximum contact on the drive side which spreads the load and improves chainring life. The narrow side allows clearance for mud and debris which reduces friction. [The] alternating wide/narrow tooth pattern prevents chain derailment.” See a graphic here.

No doubt the Wolf Tooth ring is not the only solution to a chain-drop problem. One reader who emailed me said he solved his chain-drop problem on a bike similar to mine simply by swapping his Praxis ring for a different model ring from Praxis, one that, like the Wolf Tooth model I purchased, has teeth too fat to go into the narrow plate opening, guiding the rider to place the chain properly. Another reader with a bike similar to mine swapped his original ring for a larger tooth-count one from Wolf Tooth. And I notice that on its newest ebikes, Specialized is now using a chainring from SRAM (though that may simply be because they got a better price on the SRAM ring.)

In the end, I don’t know why my original ring from Praxis started dropping my chain after I replaced the chain, and I don’t know why ensuring that I had the new chain installed on the right teeth didn’t solve the problem, though maybe the ring was too-far worn by then. But the Wolf Tooth ring solved the problem, and it’s gotten me back on the road.

These days, 1x systems are showing up more and more on new bikes, both regular and electric, and not just on mountain bikes. So this long ramble about my chain-drop problem may be useful if you encounter that on your bike.

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Stan Purdum has ridden several long-distance bike trips, including an across-America ride recounted in his book Roll Around Heaven All Day, and a trek on U.S. 62, from Niagara Falls, New York, to El Paso, Texas, the subject of his book Playing in Traffic. Stan, a freelance writer and editor, lives in Ohio. See more at www.StanPurdum.com.