Bicycle Derailleur Shifting Issues Due to Limit Screw Misalignment

To diagnose if limit screws are the cause, shift the chain to the smallest cog and observe if the guide pulley is perfectly aligned beneath it; if the chain rubs or fails to drop, the High (H) limit is incorrect. Similarly, shift to the largest cog and check if the chain attempts to overshift into the spokes or fails to reach the largest cog, which confirms the Low (L) limit requires adjustment.