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The design of ABS- or vehicle control systems by means of computer simulation needs adequate tire models. Recordings of the wheel speed during ABS control show oscillations caused by the rapid pressure changes in the wheel brake cylinder. Investigations in lateral tire dynamics show a phase shift between the slip angle and the lateral tire force. These transients can not be explained by simulation if the usual stationary tire input-output behaviour is supposed. Thus the investigation of the oscillations requires a different approach to the modelling of the tire. In a first step measurements with an experimental car equipped with a computer for data acquisition and control and with various sensors - e.g. a Rotating Wheel Dynamometer - were carried out. The measurement results showed a correlation between the oscillations in the wheel speed and the braking force caused by the pressure pulses as well as high frequency oscillations in the lateral tire forces.

High performance Antilock Braking Systems (ABS) are well known to allow for very rapid pressure changes in the wheel brake cylinders. Recordings of the wheel speed during ABS control show oscillations just after the rapid pressure changes. The oscillations can not be explained by simulation if the usual stationary brake force versus slip curves are used. Thus the investigation of the oscillations requires a different approach to the modelling of the tire. As a first step in the alternative modelling of the tire the forces and moments on the running tire were measured using an experimental car. During the measurement the pressure in the wheel brake cylinder was modulated stepwise. A new Rotating Wheel Dynamometer was used to take those measurements. The results showed that the oscillations which were observed in the wheel speed could also be found in the braking force on the tire. Contrarily, the corresponding oscillations could not be found in the braking torque.