the curve are of equal magnitude for a given steering input the associated steering angle u03b1 can be derived therefrom and consequently the steering input for the steerable wheels 3 4 5 6 can be inferred furthermore it is possible to ascertain by way of the revolution counts n 1 and n 2 or n 3 and n 4 of the two wheels 1 2 respectively and their respective revolution count changes u03b4n 1 u03b4n 2 or u03b4n 1 u2032 u03b4n 2 u2032 whether one of the two wheels 1 2 is slipping if as in the example illustrated in fig5 the revolution count changes u03b4n 1 u03b4n 2 or u03b4n 1 u2032 u03b4n 2 u2032 of the two wheels 1 2 are equal in magnitude within each pair no slip is occurring if with the same steering angle u03b1 their magnitudes differ within the pair slipping is taking place in the same way the gradients u03b2 1 u03b2 2 u03b2 1 u2032 u03b2 2 u2032 of the revolution count progressions of the wheel 1 on the inside of the curve and those of the wheel 2 on the outside of the curve can make it possible to determine whether there is slipping between the.