TURNING pairs.LESS friction and thus a long life.It is not a PERFECT mechanism as mathematically it is accurate at only 3 positions, middle and TWO extreme positions.The mechanism is on the back of front wheels.Mostly USED because the true rolling is achieved by the instantaneous center.Davis Steering mechanism:Has both sliding and turning pairs. (2 sliding and 2 turning pairs)Exact steering gear mechanism.Because of sliding pairs, more friction is generated and hence has less life.Mechanism is placed in front of wheels.