Your chain keeps coming off and jamming up your bicycle’s drivetrain. You’re probably wondering why it keeps happening and how you can fix it.
Your chain might get stuck in your derailleur due to a misadjusted, misaligned, bent, or rotated derailleur, or a dirty, worn-out, or too-long chain. Sometimes it might be due to bent or broken teeth on the chainring or the sprocket or too much tension on the cables.
Why Does My Chain Keep Dropping?
We’ve all been there; you’re riding along peacefully, and suddenly, your pedals lurch unexpectedly, and you hear a clamor come from your drivetrain. Congratulations, your chain has just slipped off.
It’s called chain drop when your bicycle chain falls off your gears while pedaling. Most commonly, it happens on the front chain ring by slipping between the crank and the frame though you can drop your chain in both the front and the rear on either side of the gear.
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The most common reason I see chain drop is because of improperly set up derailleurs on a bicycle. Although, it can happen because you have a dirty or worn-out chain.
Chain Suck Sucks
Nothing annoys me more than a squeaky chain. I’ve often thought about carrying a bottle of chain lube with me on rides and offering it to particularly noisy offenders. However, a dirty, dry, or worn-out chain will present more problems than a boisterous ride.
A lubricated chain is a happy chain for a number of reasons. Your chain is comprised of many links, and you’ll notice that it snakes around your gears at some pretty complex angles, so these links need to be free from binding. Regularly lubing your chain keeps the chain from binding and allows it to move as freely as it needs to.
If you have a chain that is starting to bind up at the links, what will eventually happen is it won’t disengage from the chainring as it goes around. That’s why it’s called chain suck because the chain gets sucked down and around the chainring.
When this happens, it can cause a lot of damage to your drivetrain because it pulls the rear derailleur forward, potentially pulling it out of alignment or into your spokes.
If you take care of your chain and maintain it well, it still gets old, worn out, and requires replacement. Chains stretch over use, and the increased slack on your chain will cause shifting issues or a dropped chain. The same applies to a chain that is too long.
Derailleur? More Like Derailment
Two derailleurs usually guide your bicycle’s chain—one on the front and one on the rear. If you have a 1x setup common on modern mountain bikes, you’ll only have a rear derailleur. If you have a single-speed bicycle, you’re better than us and don’t need this article.
The main job of your derailleurs is to guide the chain as it changes gears and to keep it on said gears. However, when your derailleur becomes misaligned, it can jam up the works and cause incorrect shifting or chain drop.
When I’m experiencing chain issues, I first check that my derailleurs are correctly aligned. The most common way a front derailleur is attached is the clamp-on style, and occasionally the clamp may loosen or take a hit and become misaligned or bent.
If that happens, your chain will rub against one side of the cage. You may only experience chain rub when you’re cross-chaining (big gear up front and small in the back or vice-versa), but if the
chain rub is excessive, it causes the bicycle to change gears unexpectedly or drop the chain, then it needs addressing.
The front derailleur is easy to align, and you can usually do it by sight. The way I do it is I shift the bike to the outermost chainring up front and the outermost sprocket on the back. I then align the right side of the cage parallel to the chain. This will fix most alignment problems.
The rear derailleur is slightly more complicated if it’s out of alignment. Most rear mech attaches to your bicycle’s frame on a derailleur hanger. What I see a lot of times is that the hanger is bent which is causing the rear mech to be out of whack.
If you’re comfortable and careful, you can bend your hanger back in place, but if it’s not something you’re up to, take it to a trusted bike mechanic to have them take a look at it.
Set Your Limit – Screws
Both the front and rear derailleur on your bicycle have limit screws. These tiny little screws do something extraordinary. They limit your derailleur. More precisely, they limit how far your derailleur can move inward or outward.
Usually labeled “H” and “L” for “High” and “Low,” respectively, these screws provide a mechanical stop for the movement on your derailleur. Having your limit screws set appropriately is crucial to stopping chain drop and can potentially save you from a severe repair bill.
Derailleur Limit Screws
I consider the rear derailleur to be the more important one to have the limits appropriately set on because if you get inside chain drop, that means the chain, and probably your derailleur arm, is about to get chewed up by your spinning rear wheel.
If that happens, you’ll be lucky to be able to salvage the rest of your ride, but what is more likely is that you’ll damage your wheel’s spokes and your derailleur while you’re at it.
The H-limit screw on a rear derailleur stops movement at the smallest cog. If your H-limit is set improperly, your chain is liable to drop off the smallest cog to the outside edge of the frame.
The L-limit screw is the one that prevents movement past the largest cog. If this limit is set incorrectly, you’ll potentially have an issue with your chain or derailleur going into your spokes.
The front derailleur is a touch less mechanically complicated than the rear mech, but it still has our old friends, the H- and L-limit screws.
The orientation of the limit screws up front is the same. The L-limit stops the derailleur from moving too far inside the frame, and the H-limit prevents it from moving too far outside the frame.
Adjusting the limits and angle of the front derailleur is essential for preventing chain drop and chain rub.
With adequately set limit screws on your bike’s front and rear mech, you will eliminate the most common cause of chain drop.
Other Causes of Chain Drop
If your chain is dropping like me on a group ride (constantly), and you’ve already checked out the most common culprits, there are a few more things to look at.
While not super common, the teeth on your chainrings or sprocket can get bent, usually from a crash, and this will cause the chain to jump or slip off. More common is that the teeth on your gearing get worn down from use. As the teeth wear down over time, shifting may get sloppier, and the gear will lose the chain.
Another sneaky cause of chain drop is having too much tension on your cables. From my experience, this presents itself by shifting too far when you click up or down a gear. If your limits are correctly set, they should stop your chain from dropping, but too much tension can push the chain too far, especially shifting into the largest sprocket or chainring.
