What are speedrings? why do I need them?

The speed rings are installed between the nut and bearing and the bearing and hanger, giving them more tolerance, also, the spacers allow you to tighten your wheels fully (so they don't jiggle). They will help keep your bearings from being damaged by horizontal forces (sliding, landing perpendicular). You have to tighten them properly, otherwise they do nothing. Speed rings even be stacked on top of each other to widen your hanger width. (if there is still space for the axle nuts).  Modern bearings van come with built-in rings