Indexing Gears With the Barrel Adjuster

Most hesitant or jumpy gear changes on a cable-operated bike come down to cable tension, fixed with the small knurled barrel where the cable meets the derailleur or shifter. Indexing means lining the derailleur up so each click moves the chain exactly one sprocket. If the chain is slow to climb onto bigger sprockets, turn the barrel counterclockwise to add tension; if it is slow dropping back to smaller ones, turn it clockwise. Work in small turns, testing the whole range each time. Recheck after fitting new cables, which can settle at first. Look at the derailleur hanger from behind first: a bent one makes good indexing impossible. Leave the limit screws, which stop the chain going into the spokes, alone unless you know they are wrong.