How to Size a Bicycle Chain, by Park Tool on YouTube. 8 min 10 s.
- Video length
- 8 min 10 s
- Time to do it
- 20 minutes
- Difficulty
- Medium
- Steps
- 8
What you need
Steps
Put the bike in a repair stand or lean it so you can turn the cranks freely. Shift the rear derailleur to the smallest cog and the front to the smallest chainring.
Check whether the old chain was the right length. With the chain on the smallest cog and smallest chainring, the rear derailleur cage should still have some tension and not fold fully onto itself.
If the old chain was correct, lay it flat beside the new chain with both ends aligned. Mark the new chain at the same pin as the old one, counting inner and outer plates to match.
To size from scratch, thread the new chain over the largest front chainring and the largest rear cog, bypassing the derailleur. Pull the ends together until the derailleur cage is nearly stretched straight.
Add two links to that point, counting one inner and one outer plate as a pair. This extra length gives the derailleur room to move through its range.
Mark the pin where you will cut. Use the chain tool to push the pin out and remove the excess length.
Join the chain with the master link or by pushing a pin back in, depending on your chain type. Check the link moves freely.
Shift through every gear combination and check the derailleur does not overstretch. On full suspension bikes, compress the rear travel to confirm the chain still has slack.
Tips and common mistakes
Always size the chain on the largest cog and chainring, not the smallest, so the derailleur is not damaged by a too-short chain.
Count links twice before cutting. A chain cut too short cannot be lengthened without adding a new section.
Bikes with chain guides or small chainrings may need a different length, so check the manufacturer's spec.
Push the pin out slowly and keep the chain tool straight so you do not bend the side plates.
Questions
Can I just copy the length of my old chain?
Yes, if the old chain shifted well and the derailleur had proper tension. Lay both chains side by side and match the pin positions before cutting.
How many links should I add with the largest cog method?
Add two links, meaning one inner and one outer plate, past the point where the derailleur cage is nearly straight.
Do I need special tools to size a chain?
A chain tool is needed to push out the pin. Master link pliers help open and close quick links, but many chains can be joined with the chain tool alone.
This guide was drafted from the video's details and general task knowledge. It has not been checked against the full video. Check the video and relevant product instructions before following a procedure. Report a correction.
