3.5 drivetrain

Chain Sizing (New Chain Length)

Chain Sizing (New Chain Length). Step-by-step procedure for bike maintenance — tools, time, and what to watch out for.

Difficulty ★★☆ moderate
Time ~15 min
Applies to All bikes

Tools

  • New chain
  • chain breaker
  • master link

Procedure

  1. Remove the old chain

    (note its length by counting links if possible).

  2. Bypass the rear derailleur

    — drape the new chain through the front derailleur, around the **largest chainring** and **largest cog**, but not through the rear derailleur cage yet.

  3. Pull the chain ends together

    until they meet snugly around the big-big combo (no slack, no stretch).

  4. Add 2 full links (1 inner + 1 outer pair)

    beyond the meeting point. This accounts for routing through the rear derailleur.

  5. Mark the link

    where you'll cut.

  6. Break the chain

    at the marked point with the chain tool.

  7. Route through the rear derailleur

    (over the upper jockey wheel, around the lower jockey wheel cage tab, under the lower jockey wheel).

  8. Join the chain

    with a quick link or by pressing the pin (see 3.6).

  9. Verify by shifting through all gears

    — chain should not bind in big-big and should not have noticeable slack in small-small. If it slaps or sags in small-small, it's too long; remove a link. > For 1x setups, "biggest chainring" means the only chainring. Same procedure otherwise. > Chains with a clutch derailleur: turn the clutch off (or push the cage forward against spring tension) when sizing, then back on after. ---

Procedure (large-large method, most reliable):

  1. Remove the old chain (note its length by counting links if possible).
  2. Bypass the rear derailleur — drape the new chain through the front derailleur, around the largest chainring and largest cog, but not through the rear derailleur cage yet.
  3. Pull the chain ends together until they meet snugly around the big-big combo (no slack, no stretch).
  4. Add 2 full links (1 inner + 1 outer pair) beyond the meeting point. This accounts for routing through the rear derailleur.
  5. Mark the link where you’ll cut.
  6. Break the chain at the marked point with the chain tool.
  7. Route through the rear derailleur (over the upper jockey wheel, around the lower jockey wheel cage tab, under the lower jockey wheel).
  8. Join the chain with a quick link or by pressing the pin (see 3.6).
  9. Verify by shifting through all gears — chain should not bind in big-big and should not have noticeable slack in small-small. If it slaps or sags in small-small, it’s too long; remove a link.

For 1x setups, “biggest chainring” means the only chainring. Same procedure otherwise. Chains with a clutch derailleur: turn the clutch off (or push the cage forward against spring tension) when sizing, then back on after.