The inherent result of cooperation of elements in a wheel-rail set is the existence of friction between a wheel flange and a lateral surface of a rail head, happening mainly on track curves. Due to the occurrence of large lateral forces when vehicle runs over track curves, it is possible to measure the magnitude of the forces at the wheel-rail contact for various vehicle's bogie structures. The new system described in this paper is based on non-direct measuring lateral forces in bogie elements. As a part of project development there where numerical calculations and experiments on a vehicle carried out. As a main issue, there where investigated stress signals from extensometers mounted on guiding elements of wheelsets. The article also presents a method of further processing of the obtained analog signal in order to eliminate the disturbances present from the useful signal. The measurement method presented in the article was used in the tests of rail vehicles.