McLAREN LOOKING FOR THE WINNING EDGE
Besides its front wing, McLaren also modified the endplates of its rear wing. The horizontal endplate slits, which aim at balancing pressure on both sides and are usually cut within the endplates, now extend outward all the way to the edge of the upper endplate (see bottom picture). This solution, which was first devised by Toro Rosso, had already been copied by Mercedes and Sauber at Silverstone. What makes the McLaren layout stand out is the length of the slits.
We have already discussed the purpose of these horizontal louvre: these serve to balance the pressure on both sides of the endplate by allowing the high-pressure air through and towards the low-pressure area. The pressure differential is thus curbed, which weakens the vortex generated in the area where the endplate and upper flap meet with the ultimate goal of reducing drag.
One can surmise that having ‘open’ slits instead of ‘closed’ ones further decreased the pressure differential because as soon as the airflow reaches the louvre it is vented to the outside. And the MP4-31 cannot afford having too much drag, given the fact that its Honda engine remains one notch behind the competition. This power deficit also limits the aerodynamic load that can be generated by the car.