A method for determining the conditions of an underlying surface during unbraked or braked travel of a vehicle by a wheel-specific characteristic variable which is derived from a change over time in the wheel speed detected at at least one vehicle wheel. According to invention there is provision that a) a jolt signal is formed by double differentiation of the wheel speed, b) in order to form the characteristic variable the difference between the absolute value of the jolt signal and a tolerance value is summed or integrated over time, and c) the condition of the underlying surface is determined by comparing the characteristic variable with an oscillation signal threshold value.