The present invention relates to a roller brake testing dynamometer (P) for vehicles whose braking forces are to be ascertained, wherein there is provided at least one roller (L) which is driven by way of a drive (A) in order in turn to drive a vehicle tire (R) bearing against the roller (L), and wherein the dynamometer (P) has at least one contact-less sensor unit (S) for detecting the position of the tire (R) relative to the at least one roller (L).