In this brief, a robust braking controller is proposed for motorcycles. Its aim is to control both longitudinal slips of the vehicle to optimal ones using a sliding mode controller. The robustness of this controller is proved with respect to change of road adherence, load transfer, and lateral movements. The optimal target slip is computed thanks to perturb and observe algorithm which is inspired from the extremum seeking algorithms. The objective of this algorithm is to seek the appropriate longitudinal braking forces and to avoid rear wheel's loss of contact. Simulations on a multibody simulator are given to enhance the performances of the controller.