Blade Grooves (Nokian WR A4) The inner shoulder’s fan-like rib pattern with functional tread blocks and Blade Grooves efficiently routes the snow and slush away from the contact surface. The sipes staggered at different angles provide effective longitudinal grip and acceleration grip on snow, in particular. Wide longitudinal grooves offer lateral grip. The excellent winter grip is further improved by the block pattern that is shaped on the inner shoulder side of the centre rib. It is partially equipped with hinges and sipes. The small, heavily siped tread blocks are grooved so that every other sipe is attached on the left and every other on the right.