Check chain wear and replace an e-bike chain

Park Tool lists two signs of a worn chain: it slips when you pedal hard, or it hangs onto the chainring when you shift under load. Before blaming the chain, make sure the shifting is adjusted and the chain is clean and lubed (Park Tool). See adjust the rear derailleur and clean and lube the chain.

A three-point checker is pushed onto the chain while you keep the chain under tension, then you read where the tip sits. A two-ended drop-in checker is hooked on and you see whether the far end drops in (Park Tool).

Line up a rivet with zero on a ruler and count 24 more rivets. The last one should sit on the 12 inch mark. If it is more than 1/16 inch past, Park Tool says the chain is worn out. This is a rough check (Park Tool).

Park Tool's general guide: 0.5% wear for 11-speed and up, 0.75% for 10-speed and below, and 1.0% for single speed. The chain maker's own spec comes first (Park Tool). iFixit suggests replacing the chainrings and cassette together with the chain (iFixit). Park Tool's approach is to replace the chain on time, and to replace the cogs if a new chain skips (Park Tool).

Shift to the largest chainring and largest cog. The chain should show two slight bends at the derailleur pulleys. On the smallest cogs it should have no slack and not touch itself (Park Tool).

For a quick link chain, find the link with the different side plates and open it with master link pliers. For a pinned chain, push out a rivet a few links away from any old connecting rivet with a chain tool, keeping the pin straight (Park Tool). Shimano says not to reuse a quick link once it has been removed (Shimano).

If the old chain was the right length, lay the two side by side and match them rivet by rivet, keeping in mind the old one has stretched. Otherwise, for rear cogs of 36 teeth or fewer, wrap the chain around the largest chainring and largest cog, find the shortest point where the ends can join, and add two rivets. For 1x setups with a 42 tooth or larger cog, Park Tool routes the chain around the ring and largest cog without the derailleur and adds four rivets (Park Tool). Shimano says not to cut a chain at the quick link (Shimano).

Any logos on the chain face outward on the drive side. Thread it through the rear derailleur, following the cage tabs, then through the front derailleur if you have one (Park Tool).

Use a new quick link made for your chain. Shimano says to fit it with the arrow pointing in the direction the cranks turn (Shimano). Seat it with the pliers, or set it on the top run, hold the rear brake and press on the pedal. For a pinned chain, use the connecting rivet made for that chain and follow its instructions (Park Tool).

Pedal backward and watch for a tight link, then flex it sideways to free it (Park Tool). Shimano says to check the chain and quick link for cracks, bends or skipping before you ride (Shimano). If a new chain skips, the cassette is likely worn too (Park Tool).