If you do all your own bike maintenance, or if you run into mechanical problems out on a ride, at some point you’ll probably have to shorten a chain.
Unless you have some prior knowledge about chains, it’s impossible to know what the optimum chain length should be. As well, it’s easy to weaken the chain if you shorten it the wrong way. So, how do you go about it?
This article tells you how to shorten a bike chain, when you’ll need to do it and the tools you’ll need for the job.
Why Would You Shorten a Bike Chain?
There are a few instances where you might want to shorten a bike chain. Shortening a bike chain is less complicated than lengthening one, so it helps to get it right first time. Below are the common reasons.
New Chain is Too Long
When manufacturers sell chains, naturally they sell them in standard lengths. These lengths are always going to be on the long side, so you buy a chain and cut it to the size you need.
A typical chain length is 116 links. That’s the type of size you’ll see on most boxes, though there might be significantly fewer links depending on bike type.
Read more: How much are bike chains?
Link & Size Definitions
Manufacturers usually count the distance between chain pins as a link, which isn’t strictly correct. There is one inch between each “proper” link on a bike chain and only half an inch between pins.
You only need remember the above if you see a chain length that seems too short in links. A real link comprises two half-links. Thus, it’s counted with every two pins and not every one. Mostly, you’ll see the pin-to-pin measurement method.
A mechanical emergency could force you to shorten your chain out on a ride. That’s when it’s useful to carry a chain tool, otherwise you’ll need a lift.
On bikes with derailleurs a wonky front mech may damage the chain, particularly when shifting to lowest and highest gears. You’d have to remove the damaged chain section and potentially ride the middle gears until you straightened things up.
As part of your repair kit out on the road or trail, it’s helpful to carry bicycle chain “master links” or “quick links”. You can reattach a chain without these, but chains that are sold with them are likely to need one for the safest repair.
Another time you might shorten a chain is if you switch to a cassette with a much smaller biggest sprocket.
For instance, if you moved house and no longer needed a super-easy gear for steep hills, you could change from an 11-34t cassette to an 11-28t or 11-25t cassette.
The benefit of reducing the cassette range is that the sprockets are closer in size to each other, making gear changes smoother.
If you make a small cassette change like a 34t to 32t, you may get away with using the same chain. The consequences of having a chain too long are not as serious as having one too small.
Cutting a chain too short can wreck a rear derailleur when you try to hit the biggest sprocket on the back whilst also on the big front chainring. You’d only cut a chain too short on purpose if it enabled you to get home in an emergency.
Read more: Compact vs standard cranksets
Shorten a Stretched Chain?
You’ll often hear people say that bike chains stretch. They don’t. They elongate as their parts wear. The tensile strength of a bicycle chain is far too great for a cyclist to stretch it by any means.
A bike chain does not need to elongate much to be considered worn, and it’s worn when it rides too high on the sprockets and begins to destroy them.
If a chain is 0.5% to 1% longer than when you bought it (depending on how many gears the bike has), it should be replaced.
One common method of measuring chain wear is with a 12-inch rule. If you place the zero mark up against the center of a pin, the 12-inch mark should be no more than 1/16” (1.57mm) past the center of the corresponding pin.
The above method is fraught with risk if you do it while the chain is still on the bike—it’s hard to trust accuracy—so a chain measuring tool is easier for many people.
How to use a measuring tool:
If both the 0.5 and 0.75 percent sides of the tool do not fit, then the chain has not stretched and is fine to ride with.
If the 0.5 percent side does fit inside, but the 0.75 percent does not, then you should think about replacing the chain soon, but it’s not urgent.
If both the 0.5 and 0.75 percent sides of the tool do fit inside the chain, you should replace the chain immediately.
To answer the original question, you wouldn’t ordinarily shorten a “stretched” chain.
The sensible course of action, especially if replacement cassettes and chainrings are expensive, is to monitor chain wear and buy new chains regularly.
A rough rule of thumb is that you might get through three chains before needing to replace a cassette. The front chainrings wear down much more slowly than cassettes (at least 3x), particularly if the cyclist avoids the lateral force of “cross-chaining”.
Before You Start: Tools You’ll Need
Having identified a need for shortening your chain, what tools will you need? Out on the road, you’d need a chain tool on a multitool as a bare minimum. (Be aware that the pins on these tools tend to be more fragile, so inspect them after use.)
Let’s assume you have the luxury of being able to shorten your chain at home. This is what you’ll need:
- Chain tool
- Master link (aka quick link – various proprietary names)
- Master link pliers
- Chain hook / installation tool
The master link pliers are useful because It’s not always easy to disengage quick links by hand. Out on a ride, you can use a piece of cable to pull the link inwards and achieve the same thing.
A chain hook is useful for holding the two ends of a chain in place and under tension if you’re working on the chain in situ.
If you don’t have a chain tool, you’ll need the following:
- Master link
- Small nail or punch
- Pliers or a piece of wire
You’ll also need a firm surface to hammer on, be it a bench worktop or piece of wood.
How To Use a Chain Tool to Shorten a Bike Chain
A dedicated chain tool is a useful thing to have at home or even on rides, though more comprehensive multitools often include them.
Below is a step-by-step guide on how to shorten a chain with a chain tool.
Step 1. Calculate the Correct Chain Length (for New Chains)
If you’re repairing a chain out on the road, you won’t need to calculate required chain length. You’ll just remove as few links as possible to make the repair.
With a new chain you have a few options for calculating required length. You can use a chain-length calculator and count the links one-by-one. You can lay it alongside your old chain and remove any extra links that are evident.
A third way to ascertain chain length is to measure it whilst wrapped around your biggest rear sprocket and largest chainring on the front. The process is carefully described in the Park Tool video below.
Video: How to Size a Bike Chain
Step 2. Locating the Master Link (or not)
It’s easier to break the chain and join it with a master link, but most of them are not “officially” reusable. Thus, when you’re shortening a chain for whatever purpose, you’ll do it with a chain breaker and use a new master link to rejoin it.
If the master link is, in fact, reusable, you can locate this before disconnecting the chain and removing part of it. This doesn’t apply to a repair unless it happens to be adjacent to the master link.
Step 3 Break the Chain
Once you’ve located the point at which you must break the chain, you lower the chain over the furthest support on the tool so it is braced against the end.
Then, screw the handle of the tool slowly clockwise until the punch rests on the center of the chain’s pin. Continue turning clockwise to drive the pin (or rivet) out of the far side of the chain. The chain is broken.
Important: if this is an emergency repair and you have no master link on you, you must not drive the chain pin completely out. When you meet with resistance the second time, with a small part of the pin still protruding inside, stop and leave the pin where it is. You can still break the chain with a little coaxing.
Video: Using a Chain Tool to Break a Chain
Step 4. Remove Chain Link(s)
If this is a new chain, you only need break it once to shorten it. But if you’ve taken it off your bike, you’ll need to break it again.
When shortening the chain, you must pay attention to the ends. If you’re using a master link, you’ll need them both to be narrower inner half-links, because the master link acts as an outer-plated half link joining two inner links together.
Shortening a chain without a master link or with a Shimano replacement pin, you’d need asymmetrical chain ends.
Step 5. Reconnecting the Chain
The easiest way to reconnect a chain with a master link is to position it precisely over the pin ends and tighten the chain by rotating the pedals.
To complete the emergency repair discussed in step #3:
Having cut off a damaged section of chain and joined asymmetrical ends together, you must push the half-removed pin back from whence it came. You’d do this with your chain tool, placing the chain over the nearest support to the punch.
Gradually move the displaced pin back through the hole on the far outer plate. Don’t overdo this, as the pin should only protrude slightly.
If you perform this repair on a fully peened, non-reusable chain pin, you will weaken the chain and should replace it as soon as possible.
How To Shorten a Chain Without a Chain Tool
If you are working with a new chain, you’ll first have to work out the ideal length. See step #1 above for that.
There are a couple of ways to brace the chain during this process. You can use a vice, but this is the everyman method:
Step 1. Look For a Master Link
If the chain is still on the bike, you ideally need it to have a master link so you can easily remove and later rejoin it. Without a master link, you’ll still be able to break and shorten the chain, but joining it again will be trickier.
Use a pair of narrow pliers or a piece of cable to open the master link if there is one.
Step 2. Break the Chain
Position the nut on a firm striking surface. Identify which pin you want to knock out, and position it over the nut. Place a nail or punch directly over the center of the pin and hammer it out.
Do not hammer the pin completely out if the chain is incompatible with master links.
Step 3. Remove Chain Link(s)
If you’re reconnecting this chain with a master link, again you need the chain ends to be identical narrow segments. With a new chain, that means you’ll be removing two half-links (1 full link) at a time to shorten it.
Join the chain again by pushing on the pedals to click the master link into place. Without a master link, you’ll need to hammer the pin back into position.
And We’re Done…
Knowing how to fix a chain is an important skill, especially out on a ride. It’s a different ball game to swapping out a tube.
We hope this article may have armed you with enough confidence to try chain installations and repairs on your own. Chain work can be a messy process without gloves, but if you keep your calm there’s no reason why you can’t do it yourself.
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