Derailleur Alignment
When it comes to rear derailleur performance, alignment is key. Cassette cogs are barely more than half the width of a chain apart from one another—preventing chain jumps across cogs under power and maintaining proper indexed shifting requires that the derailleur pulleys remain in perfect alignment with the cogs. No amount of barrel adjustment and limit screw fiddling will correct for a misaligned derailleur hanger—any shop worth their service tag knows that the first step in most any derailleur adjustment is checking the derailleur hanger alignment.
