Macpherson strut has no upper a arm, just the lower suspension arm. Basically it is made of a spring over a damper pivoted on a ball joint on the sole lower arm. It is attatched to the vehicle at the top by a roller bearing. This has the advantage that the strut is the load bearing member as opposed to the shock absorber. Steering is achieved by attatchment either directly to the lower end of the shock absorber or to an arm off of the spindle.
Double wishbone has an arm on the top and bottom. Because of the additional control arm up the top the load bearing component is independant of the geometry control componet. This minimises effects like brake steer, unwanted toe changes under acceleration and cornering.
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HERE for an article on Honda double wishbone setups.
