Chain sizing and installation

Chain Sizing and installation

Normally when you change a chain on a bike you cut the new chain to match the one you are removing. In this case we do not have a reference to go by, so we must size the chain accordingly.

The best way to do this is by looking at the extremes. The shortest extreme is when the chain is on the the smallest chainring and the smallest sprocket on the cassette. Conversely, the longest requirement is when the chain is on the biggest chainring and the largest sprocket. We need to find a length that satisfies both of these conditions.

To begin with we are going to make a tool that will assist you in holding the chain while confirming the correct length.

Use a piece of wire (coat hangar or similar) and bend it as follows. Note that it is a little over two inches long and picks up the proper spacing of the chain.

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So lets look at the longest chain condition first. (chain on smallest sprockets)

Adjust the front derailleur to the smallest chainring and install the chain over the smallest chainring as seen below.


Adjust the rear derailleur to the smallest sprocket and thread the chain over the sprocket and though the derailleur as shown.


Now using your wire tool join the chain ends together and fashion the wire to hold the chain.


Now look at the arm on the derailleur. Confirm that the chain does not conflict with the derailleur arm. If it does make chain shorter by adjusting it in your wire tool. Adjust length till the chain has clearance from the derailleur arm as shown below. (Note: my chain satisfies this without the requirement of trimming any links)


Now let’s look at the shortest chain length requirement (chain on largest sprockets).

Adjust the front and rear derailleurs to the largest chain ring. You will have to lift the chain and move it to the big sprocket. If it’s too difficult you can remove the wire tool from the chain (record position) and rework the chain onto the large sprockets (front and rear).

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Confirm the rear derailleur arm is not fully extended. Meaning it still has a little swing left before it bottoms out. If so, then you are good to proceed to joining the chain at its current length.


The chain is joined using a pin and a chain break tool to push the pin in place. The tapered end of the pin is inserted first.

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Then use the chain break tool to press the pin into position. Pay close attention to how far you press this pin through.

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It should look like this when inserted.


Use a pair of plier on the tapered part of the pin sticking out on the backside of the chain. Wiggle the pin and it should snap off.


Check to make sure the link you just pinned rotates freely. If it’s sticky, you can bend the chain by hand (across the link) a few times to open up the tightness in the pin.



Test out the chain by turning the crank and shifting through the gears. Don’t worry, the derailleurs will get final adjustment in a later step.

Proceed to Brake line trimming

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