Assembly comprising a vehicle (13, 13a-c) having a plurality of wheels (2), each of the wheels (2) arranged to support a weight of the vehicle (13) against an underlying surface (5); a sensor (10) operable to measure a force between one of the wheels (2) and a body of the vehicle (13, 13a-c); and a processor (15) configured to receive measurement data from the sensor (10). There is also provided a method for measuring conditions of a drive surface (5) and a method of operating vehicles (13, 13a-d) on a road (5).