FIA CLOSED REAR DIFFUSER LOOPHOLE USED BY SOME F1 TEAMS

Mercedes GP rear diffuser

McLaren, Mercedes GP, Renault and Force India will have to make modifications to their rear diffuser designs in time for the Australian Grand Prix, after FIA reconed that as going against the spirit of the article 3.12.7:

"A single break in the surface is permitted solely to allow the minimum required access for the device referred to in Article 5.15."

There is no specific definition of what the 'minimum' size is though - so some teams have been using exotically shaped starter motors to allow themselves to feature wide-shaped holes in the diffusers. This concept was pioneered by Brawn GP in 2009.

Such a hole in the diffuser helps create another tunnel for air to flow through - which as well as helping to produce more downforce, also ensures such downforce is more consistent throughout a lap - especially under braking, when the rear of the car rises up and the airflow can stall.