What happens if my bike chain is too short or too long & how to fix it?

Your bike’s chain is a key component of your bike that enables you to transmit power to the rear wheel. If your chain is improperly maintained, it could break while you’re riding, damage other components, or just make your rides noisy and bumpy. 

If your bike chain is too short, it will quickly wear out parts of the derailleur, or the chain itself might even break. If the chain is too long, it will often skip upon exerting ample torque, and it will also likely fall off the chainring and freewheel and will get jammed in your drivetrain.

Here’s a quick primer on how to make sure that your chain is properly sized, ensuring that you’re not causing unnecessary wear on your bike’s drivetrain or increasing your odds of dropping your chain.

What effects does a too short bike chain have?

A bike chain that’s too short will wear itself out more quickly. Bike chains naturally stretch over time, but having a chain that’s too short will cause your chain to undergo far more stress than it should. This means that your chain is likely to break while you ride, causing your ride to reach an abrupt stop.

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More importantly, however, bikes with rear derailleurs use a pulley mechanism to take the slack out of your chain as you switch gears. It’s important to leave enough slack in your chain for this pulley to rest gently within its designed range of extension. 

If your chain is too short, your derailleur pulley will be cranked to its limit, putting a lot of stress on both your chain and your derailleur. If you’re lucky, you’ll break your chain. If you’re unlucky, you could wear out components in your derailleur incredibly quickly or even snap part of the derailleur off.

How can I tell if my bike chain is too short?

To see if your chain is too short, shift your bike into the biggest gears in the front and back and look at the rear derailleur. The large cogs will stretch out the chain at both ends. 

If the rear derailleur pulley still has a bit of bend to it and causes the chain to travel in a slight “S” shape, your chain is not too short. If the pulley is stretched tight and the chain makes a straight or mostly straight line through it, however, your chain is too short and should be replaced.

What happens if my bike chain is too long?

When your bike chain is too long, you’ll likely experience issues with the chain ending up in places you don’t want it. This might mean odd shifts, the chain dropping off of the cogs at the front or rear of your bike, or annoying jams in your drivetrain. The chain will often skip when you exert significant effort and ample torque.

Additionally, without uniform tension across your chain, you’ll often load your chain unevenly and cause it to experience more stress than it should. Between this extra load and the wear your chain will experience from getting caught everywhere, it’s much more likely to break than a properly sized chain.

How can I tell if my bike chain is too long?

Just like with a short chain, shift your bike into the gears that will challenge your derailleur the most. In this case, since we’re troubleshooting a long chain, shift into the smallest cog in both the front and the rear. 

Examine your derailleur and look at the chain. If the derailleur can pick up the slack in the chain and the chain is mostly taut, your chain isn’t too long. However, if the chain is visibly sagging, or if it touches itself in the bend in your derailleur pulley, it’s definitely too long. You’ll need to remove some links or replace your chain.

What can I do if my bike chain is too short?

Most bike mechanics think the best way to fix a short chain is to replace the whole thing. Bike chains are fickle parts that don’t work very well when you replace individual links, so it’s usually not a good idea to add links to your existing chain. Instead, you’ll want to replace the whole thing.

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The good news is that bike chains aren’t super expensive. The bad news is that replacing a chain will involve some tools you might not have at home. It’s never a bad idea to outsource this task to a professional bike mechanic if you have any doubts.

What can I do if my bike chain is too long?

Unlike a short chain, the fix for a bike chain that’s too long is simple: remove some links. Bike chains are made up of links that are held together by rivets. 

With the proper tool (or a hammer, a pin, and a lot of patience and dexterity), you can pop out these rivets and make the chain as short as you’d like. This means that as long as you have a chain breaker and a connecting rivet, you’ll be able to knock out a few links, and you’ll be good to go.

While this might sound simple, changing out bike chains is never as easy as it sounds. You’ll need to figure out the correct length for your new chain, pop out a rivet in the right place, and then install a connecting rivet. 

If anything goes wrong, you might have to buy a new chain to fix your mistakes. Between the tools, measuring, and chance for error, it’s definitely not a bad idea to leave this operation up to the pros.

How do I size a chain for my bike?

If you fit a new chain to your bike, the chain will always come with extra links. Shift your rear derailleur to the smallest cog and shift the front derailleur to the largest cog. 

Thread the chain over the biggest cog in the back, then turn it around the biggest cog in the front until it reaches the five o’clock position. Next, pull the other end of the chain out from under your rear derailleur and bring it to the end of the other piece.

Your next step will be to figure out where you can meet the two ends of the chain. This means matching an inner shell to an outer shell on a connecting rivet chain or using half of your master link to connect with an inner shell on a master link chain. 

In either case, figure out where the two ends would meet. Next, move two rivets down the chain to make some slack for your derailleur. This is the place you’ll want to cut the chain on almost all bikes. Exceptions include SRAM 1x systems with big cogs in the back and no suspension and other unusual combinations of cogs and derailleurs.

Sam Benkoczy

Hi, I'm Sam. I own and maintain 6 e-bikes, 15 regular bikes (road bikes, folding bikes, hybrid bikes, city bikes among others). I learned about bikes from my local bike mechanic as well as from bike maintenance courses. I love being out there in the saddle, and using my bike as a practical means of transportation. You can also find me on my YouTube channel at youtube.com/bikecommuterhero Say hi to me at sam@bikecommuterhero.com.

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