Replacement chains for bicycles are always longer than you need.
In this video we'll take you step by step through chain sizing.
Hello, Calvin Jones with Park Tool company.
If you're working on a bike with a single speed, or a bike with a Campagnolo derailleur,
we have separate videos that cover sizing for those systems.
Before we begin, let's define the chain types.
There are master link chains and connection rivet chains.
Master Link chains use two removable outer plates to connect the chain.
Connection rivet chains use a special rivet to connect the chain.
Tools needed for sizing are a chain tool to cut the chain,
and you'll need a master link pliers for chains with master links.
Lastly, if you'd like to learn other procedures and concepts related to chains,
be sure to check out our guide to chains for an overview of what we have available.
Before we remove the old chain, we need to confirm it's the correct length,
so we'll shift to the largest front and rear sprockets.
The chain should be able to make this shift, and it should have two slight bends, one at each pulley.
Next, shift to the smallest sprockets.
There should be no slack in the chain,
and the derailleur should not pull so far back that the chain contacts itself.
So in this example, the chain is sized correctly and can be used to size our new chain.
Now we remove the chain, and an option is to first remove the wheel.
This takes tension off the chain, and makes things a little easier.
Inspect the chain for a master link.
If a master link is present, use a master link pliers such as the Park Tool MLP-1.2 to disengage the link.
Alternatively, you could use needlenose pliers, but it's difficult at best.
And doing it by hand is extremely difficult.
If you have a chain tool, and your chain is worn out, you could ignore the master link
and simply break the chain the same way you would on a connecting rivet chain.
We'll walk through that process next.
Connecting rivets will appear visually different from the other rivets.
When selecting a rivet to break, be sure it is at least a couple links away from any connecting rivet already installed in the chain.
Install the chain tool, and bring the driving pin of the chain tool into contact with the rivet.
Ensure the chain tool pin is driving in a straight line into the chain rivet.
Turn the handle with force and drive out the rivet.
Remove the chain.
If the old chain is an acceptable length, lay it next to the new chain as shown.
Always line up ends with outer plates.
This example is incorrect because we have an end with outer plates being compared to an end with inner plates.
Insert the master link to get a true side by side length comparison.
In this other example, neither end of the chains have outer plates
so in this case we would line up inner plates at either end.
Next we line up the chains.
Take care to match them rivet by rivet, noting that old chains will lengthen as they wear.
This is the rivet that we will cut on the new chain.
...and the chain is sized.
See this other video for a full walk through of the installation process.
When we are not matching the length of an old chain, we use the largest cog and largest chainring method.
The vast majority of drivetrain manufacturers use this method.
There are some exceptions and considerations, and we'll cover those after we show you the process.
First, shift the front derailleur over the largest chainring, and the rear derailleur to the smallest cog.
We begin by wrapping the chain around the largest cog.
If the new chain has one end with an outer plate, it should be routed toward the front chain ring.
Pass the chain end through the front derailleur cage onto the largest front chainring.
Hold at about the 5:00 position.
If the chain uses a master link, install half of the master link.
This will account for the extra 1/2 inch the master link provides.
With this plate installed, the rest of the process is the same for master link and connection rivet chains.
Pull the lower section of chain snug, and engage it on the chain ring.
Make sure the chain is fully on the largest cog.
Note that we bypassed the rear derailleur altogether, and extra length will be added to account for this later.
Now we find the closest rivet where the two ends could be joined.
The inner plates on this link would match up with the outer plates on the other link.
Because they can be joined here, we'll call this our reference rivet.
From that rivet, we add an additional two rivets.
This is the cutting point.
In can occur that when we pull the lower section snug, an outer plate meets an outer plate.
This cannot be our reference rivet because it is impossible to join the chain here.
So me must add another rivet, making this our reference rivet.
From here, we would add two additional rivets.
This is our cutting point.
We cut the chain with our chain tool
and the chain is sized.
and that is the common largest cog to largest chainring sizing method.
For a walk-through on installation, see this other video.
There are a few exceptions to the rule of adding two links, as well as some other considerations.
If the bike uses a chain guide, be sure the chain is routed through the system before determining chain length.
Add the same 2 rivets as before to establish the cutting point.
The amount of rivets added is different if you have the following combination of components:
A SRAM derailleur with an 11 or 12 speed cassette. and a single front chainring with no suspension.
With this system, add four rivets from the reference point. This would be our cutting point.
The next consideration deals with rear suspension bikes.
The distance between the rear cogs and the front rings will change as the suspension moves for bumps.
To account for that, we disconnect the shock
and compress the linkage.
This is the maximum possible distance between front and rear sprockets.
With the suspension held in place, we use the same technique as before, adding two rivets for the cutting point.
Again this is for all bikes with rear suspension, including SRAM 11 and 12 speed 1X systems.
Thanks for watching this repair help video from Park Tool.
We're constantly adding videos and articles here on YouTube as well as our website at parktool.com
Please give this video a thumbs up if it helped you out.
and of course, subscribe for the latest content from Park Tool