Bicycle Chain Skipping or Slipping While Pedalling
The most common cause is a worn chain or worn sprockets. Check the chain with a chain wear indicator tool – replace it if elongation exceeds 0.75%. Clean the chain and lubricate it with chain oil. Check the derailleur limit screws (H/L): the chain must not jump beyond the smallest or largest sprocket. Tighten the derailleur cable tension slightly if the chain slips under load. If the sprockets are heavily worn (shark-tooth-shaped teeth), they must also be replaced – ideally as a set together with the chain.