These are first quality, unshielded ball bearings with minimal rolling resistance and excellent lateral stability. Why should I choose shielded versus unshielded bearings? Is one better or faster than than the other? As with all such questions there really is not a simple answer. The racing surface of a track has some degree of worn tire material and dust present. A shielded bearing helps to keep this material out of bearing for as long as possible. An unshielded bearing picks up foreign materials much easier that can combine with bearing lubricant to increase the rolling resistance. Unshielded bearings require very regular cleaning and lubrication. Shielded bearings not so much. In both cases you need to use a high quality lubricant and use it sparingly.