A rim assembly comprises a rim including a peripheral rim portion for the mounting of a wheel; a wheel cover affixed to the rim and configured to rotate about an axis of the rim; and an oscillator attached to the wheel cover and configured to move back and forth between a first position and a second position based on rotation of the wheel cover about the axis. The oscillator is configured to protract axially away from the wheel cover when moving from the second position toward the first position and to retract axially toward the wheel cover when moving from the first position toward the second position.