Teach you how to determine the chain length of a bicycle

Methods to determine chain length

Method #1: Size to old chain (count links)

If your old chain was sized correctly, it can be used to determine the length of your new chain. To check if it was the correct size, shift the bike to the smallest sprockets and check the chain for any slack. There should be no slack in the chain, but the derailleur should not pull back far enough for the chain to make contact with itself.

Next, shift to the the largest front and rear sprockets. The chain should easily make this shift, and have two slight bends at each pulley.

Once you’ve determine your old chain was sized correctly, remove the chain and lay it out on a flat hard surface. You can either lay out the new chain next to the old one (ensuring that it is lined up link by link to eliminate any disparity due to chain wear) or simply count the links on the old chain, and cut the new chain to match the number.

Method #2: Largest cog and largest chainring method

The easiest way to determine bike chain length is the largest cog to largest chainring method.

1. Once the old chain has been removed, shift the front derailleur to the largest chainring, and the rear to the smallest.
2. Wrap the new chain around th the largest chainring (at the rear), making that if the chain has an outer plate, it is routed toward the front chainring.
3. Pass the chain through the front derailleur cage and onto the largest front chainring.
4. Hold chain at the 5 o’clock position.
5. If you are using a masterlink chain, install half the masterlink onto the front end of the chain to account for the extra half link the master link provides.
6. Pull the lower section of the chain stug towards the front chainring, bypassing the derailleur altogether.
7. Find the closest rivet where the two ends could be joined and add 2. This is your cutting point.

Method #3: Chain sizing by equation

It is possible to determine chain length from a simple equation before you even take your new chain out of the box. Remember, you can only join the inner plates to the outer plates of a chain, so you can only calculate to whole inch increments.