1. A method for characterizing a road surface encountered by a driven wheel of a vehicle, wherein the vehicle includes a torque converter providing a fluid couple between an input shaft driven by an engine and an output shaft coupled to the driven wheel, the method comprising: determining a first measure based on a first value representative of a current rotational speed of the input shaft and a second value representative of a current rotational speed of the output shaft; determining a second measure based on successive values for the first measure, the second measure being representative of a rate of change of the first measure over time; generating a set of successive values for the second measure; and identifying the characteristic based on the set.