In simplest terms, siping adds many hundreds of biting edges to the tread. The tread blocks flex under load, when they encounter an obstacle, and even when the tire simply turns. This flex exposes the biting edges that add traction and also squeegees water away to reduce hydroplaning. The same dynamic occurs during braking. Offroad Design's Stephen Watson reports better traction even on Moab's dry slickrock. The owner of this CJ-5 preferred adding sipes for icy roads instead of installing ice studs.