garbage! the biggest reason cars don't over take is because they can't get the slip stream that F1 cars of old do. most of the aerodynamic parts of the car are not there to aid downforce but to spoil the airflow as it comes off of the rear of the car. the diffuser is the worst offender in this as the steep angles used allows the air being extracted from the underside to be thrown up at high velocity. the cars travelling along behind then have to cut through this wall of turbulance. this is why invaribly the lead car will always pull away from the pack as this car has clean air to cut through. if you don't believe me then look at any race held in the wet. all that spray doesn't come off of the tyres alone does it.