How to design a McLaren P1
The secret of the P1's downforce, then, is the diffuser. Or more specifically, how much space Frank and his team could create between the floor and the top of it. The more you can make the air expand as it comes out the back, the more it'll suck the car down. Which he why he used a double diffuser, the sort that caused trouble in F1 a few years back.
Those of you with eyes may've seen a difference between the P1 unveiled in Paris and the final production version shown more recently at Geneva. On the Paris car, the rear honeycomb effect - where the taillights normally sit - was filled in, but on the production car it was hollow. "The rear of the car is designed to get all the heat out," Stephenson says. "We want to get the maximum heat out of the car so we thought, ‘lets get rid of the taillights as they take up a big area'. But that forced us to make a very thin strip of lights along the trailing edge."