3.15 Aerodynamic influence :
With the exception of the cover described in Article 6.5.2 (when used in the pit lane), the driver adjustable bodywork described in Article 3.18 and the ducts described in Article 11.4, any specific part of the car influencing its aerodynamic performance :
– must comply with the rules relating to bodywork ;
– must be rigidly secured to the entirely sprung part of the car (rigidly secured means not having any degree of freedom) ;
– must remain immobile in relation to the sprung part of the car.
Any device or construction that is designed to bridge the gap between the sprung part of the car and the ground is prohibited under all circumstances.
This is just a statement and exact method of tests follow in Article 3.16. The problem is that the tests(3.16) are not enough to satisfy the spirit of the rules(3.15)