Abstract: The quality of the tread of profile of railroad wheels is measured in a contactless manner by illuminating the circumferential wheel surface with a light or radiation source directing its radiation at least approximately in a radial direction onto the wheel surface to form a light intersection image or a light edge image of the wheel profile or tread. A sensor or sensors such as cameras, scan or sense these images by receiving light reflected by the wheel surface to produce analog signals representing the quality of tread or profile. These analog signals are digitized and supplied to a central processing unit for evaluation to provide information regarding the wheel quality. The illuminating and sensing can be performed while the wheel or wheel set is stationary or while it rolls through a measuring station, whereby it is not even necessary to remove a wheel from its vehicle for inspection.