Vehicle dynamics is today of great importance in automo- tive industry. Indeed, over the past few years, automo- tive engineering has been characterized by rapid growth in active systems. Many research works have therefore been devoted to the control of such active subsystems, as braking, steering or suspension actuators. In particular the control of suspension systems still remains of interest since this subsystem in uences comfort and road handling as well [1, 2, 3]. More recently the use of di erent actua- tors (braking, steering, suspension ...) has shown to allow for emergency situations such as rollover, too large lateral and yaw accelerations, slipping .... [4, 5, 6]. However, as emphasized by Matteo Corno and Sergio Savaresi much less work have been devoted to motorbike control, in particular in sport industry. The aim of the paper is then to bring some contribution for Traction Con- trol applications. Indeed some new methodology for ex- perimental identi cation of engine-to-slip dynamics is pro- posed, leading to the analysis of the interest of throttle or spark-advance actuators for slip control respectively. First, the authors present two algorithms that can be used for wheel speed measurements. It is emphasized that both solutions lead to some estimation delays, which de- pends on the type and chracteristics of the sensor. The core of the paper concern the identi cation of engine-to- slip dynamics using as input variable, either the throttle position, or the spark advance. First it has been shown in this paper that the modelling of the throttle-to-slip system can be approached by a switch- ing system with two modes, since it better approximates the full "harmonics" model. Then the delay issue has been discussed and the im- portance of taking into account the time-delay in con- trol design has been emphasized. It appears that some recent methodologies in observation and control of time- delay systems, could be planned, as the ones proposed in [11, 12, 13].