A cyclist writes in – they have a problem with their bike chain falling off.

Do you have a similar situation? (I know it’s happened to me before!) I’ll show you how to fix a bike chain that keeps falling off.

“Why does my chain keep falling off?”

Dear Levi,

First of all I want to thank you for the Weekly Wrench. I’ve learned a lot from this site about basic bike repairs.

I want to ask you about my problem. Every time I ride my bike and bumps into something – like speed bumps – my chain keeps on falling from the big chain ring to the middle chain ring and from the middle to smallest chain ring. I have a Truvativ firex GXP crankset, a shimano deore xt shifter (M760) and an xtr front deralleur. Are these three compatible with each other? Is it my derailleur or my shifter that is causing this problem?

Also, I noticed a rattling sound in my front shifter everytime the indicator is on the middle, but the sound disappears when the indicator is either on the top position (big chain ring) or lowest position (small chain ring).

Thank you. Hope you can shed some light into my problem.

Bump

Hi Bump,

I’m glad my site has helped you so far! Hopefully I can help with this…

The good news is that the problem isn’t uncommon – chains are always dropping off the rings. It happens on rough trails even with a perfect setup, but it shouldn’t happen on smaller impacts like speed bumps.

Based on the symptoms you shared, you probably just need a quick front derailleur adjustment or a change in chain length.

But there are many potential reasons this happens, so for the sake of a thorough answer, let’s see how to fix a bike chain that keeps falling off.

Reasons why your chain keeps falling off

Here are the potential causes, followed by how to remedy the issue.

Your chain is too long.

The chain might be too long. If it’s not pulled tight enough around the rings, it could drop more easily.

Here’s a helpful guide to chain length from Park Tool.

Your front derailleur needs adjusted.

The front derailleur might need adjusted. The lower limit screw might be allowing too big of a gap on the inside of the ring, which is allowing your chain to keep falling to the inside.

Be sure both limit screws are adjusted properly so your chain does not fall to either side of the chainrings.

Here’s a helpful guide to front derailleur adjustment from Park Tool.

Your drivetrain is worn out or incompatible.

Adjustments won’t help if your drivetrain is worn out. A worn out or damaged chain or chainring could certainly cause issues like this.

Have a trusted shop check the condition of your chain, chainrings, and rear derailleur hanger.

New drivetrain? Make sure your chain is compatible with the rest of it.

Poor gear selection.

It’s possible you are using a gear combination that puts the chain in a delicate position. If you are in the big ring and a big cog (cross-chaining), it’s likely that the chain will drop like this. Maybe not when you’re just riding along, but as soon as you hit a small bump, that’s enough to push the chain over the edge.

Try to keep the chainline as straight as possible (i.e. big ring and smaller rear cog) and see if that helps. Here’s my guide to proper chainline.

You can also learn more about shifting technique in my guide, A Complete Beginner’s Guide to Bicycle Gears & Shifting.

You need to ride smoother.

Maybe you are hitting bumps too hard! It’s unlikely this is an issue, but riding smoother always helps! 🙂

As for the noise in the shifter, if the shifter still shifts fine, I wouldn’t worry about it. The rattling is probably just the indicator itself and not part of the shift mechanism. If you checked to make sure no bolts are working themselves loose, you’re probably good. But I can’t diagnose the rattle virtually so you’d be best served by a local bike shop.

This article was originally published on March 25, 2008. It was updated and republished on July 25, 2020.

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By on July 25, 2020   /   Bike Repair, Road Cycling Articles   /   Leave a comment
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