Polishing a crank removes small imperfections, tiny surface scratches imperfections and cracks and reduces the amount of oil that sticks to it.
As the crank splashes in the oil the smoother it is the less drag is created.
Older discussion on this topic is here.
What have you discovered to be the benefits of a polished crank? What other crank mods are worth thinking about doing? What is a nightrided, knife-edged crank?
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