Weight that is rotating while the bike is moving, particularly referring to the wheels. Weight near the perimeter of a wheel has about twice the stored energy of non-rotating weight on a bicycle when moving. Rotation of cranks, wheel hubs, and other parts are of little significance because the radius and speed of rotation are small. Rotating weight resists acceleration (or deceleration), so lighter wheel rims, spoke nipples, and tires allow slightly quicker acceleration. There is no significant difference between rotating and non-rotating weight when at steady speeds or for hill climbing.