provided with slotted flaps of corresponding dimensions in fig5 is illustrated a possible construction of this kind in which the airfoil comprises three interconnected members 110 111 112 delimiting slots f 1 f 2 appropriate to define the desired flap in a conventional manner finally according to the invention the frontal plane of the airfoil can be either negatively or positively dihedral shaped a negative dihedral shaped airfoil will be employed to the end that the relative air speeds induced during turning i e tilting phases of the motorcycle are directed according to the half opening i e half span of the airfoil in this way the formation of rolling moments due to the aerodynamic action are prevented or are made capable of either contrasting with or adding to the motor vehicle tilting produced by the driver in order that said conditions are valid at each point of the airfoil the latter will show an arcuate frontal projection as illustrated by airfoil 11 39 in fig3 in such a case the camber or tilting center cc of the airfoil will coincide with the ground wheel contact center and the air relative speeds w r as induced by the rolling motion at each point of.