Method for determining the axial wheel tyre thickness of a rubber-sprung railway wheel of a rail vehicle which comprises a disc wheel body, a wheel tyre made of steel and an elastomer ring, as an elastomer part and elastomer suspension element, arranged in a prestressed fashion between the latter, wherein - over the course of the driving operation the wheel tyre thickness gradually decreases, as a result of material erosion on the wheel tread, up to a predefined wheel tyre minimum thickness at which a safe wheel tyre running distance has ended and replacement has to take place, wherein - the method is carried out with a device which is arranged on the rail vehicle and has the purpose of indirectly determining the wheel tyre thickness, in which device the elastomer ring, in addition to its function as an elastomer suspension element, is a component of a sensor system of the device, which comprises the elastomer ring as an elastomer temperature source, at least one elastomer temperature sensor (14, 15) which is assigned to the elastomer material, and at least one ambient temperature sensor and a measuring and evaluation unit which is directly or indirectly connected to the sensors (14, 15, 17), and - the elastomer ring is dimensioned in such a way that a safe, failure-free elastomer ring running distance with largely identical deformation properties is longer than the safe wheel tyre running distance which makes exchange necessary as a result of wear on the wheel tyre, characterized in that the device is used to detect, as a measuring condition, both the occurrence of a predetermined respectively identical driving operating state which repeats with staggered timing during the driving operation as well as a balanced temperature state with a constant elastomer temperature and ambient temperature, - in that when the measuring condition is detected a measurement process is started, and/or when a measuring condition is constant a plurality of measuring processes are started in succession, and during a measuring process the difference temperature (ΔT) between the elastomer temperature which is higher as a result of flexure work and the lower ambient temperature is measured, - in that every difference temperature (ΔT) which can be measured during the measuring process is assigned an empirically determined wheel tyre thickness, and this assignment is stored in a characteristic diagram in the device and/or predefined by means of a stored computing operation, and - in that after a measured difference temperature (ΔT) the assigned wheel tyre thickness is read out of the characteristic diagram and/or is determined by means of the computing operation and is available as a wheel tyre thickness measurement signal for further use. - over the course of the driving operation the wheel tyre thickness gradually decreases, as a result of material erosion on the wheel tread, up to a predefined wheel tyre minimum thickness at which a safe wheel tyre running distance has ended and replacement has to take place, wherein - the method is carried out with a device which is arranged on the rail vehicle and has the purpose of indirectly determining the wheel tyre thickness, in which device the elastomer ring, in addition to its function as an elastomer suspension element, is a component of a sensor system of the device, which comprises the elastomer ring as an elastomer temperature source, at least one elastomer temperature sensor (14, 15) which is assigned to the elastomer material, and at least one ambient temperature sensor and a measuring and evaluation unit which is directly or indirectly connected to the sensors (14, 15, 17), and - the elastomer ring is dimensioned in such a way that a safe, failure-free elastomer ring running distance with largely identical deformation properties is longer than the safe wheel tyre running distance which makes exchange necessary as a result of wear on the wheel tyre, - in that when the measuring condition is detected a measurement process is started, and/or when a measuring condition is constant a plurality of measuring processes are started in succession, and during a measuring process the difference temperature (ΔT) between the elastomer temperature which is higher as a result of flexure work and the lower ambient temperature is measured, - in that every difference temperature (ΔT) which can be measured during the measuring process is assigned an empirically determined wheel tyre thickness, and this assignment is stored in a characteristic diagram in the device and/or predefined by means of a stored computing operation, and - in that after a measured difference temperature (ΔT) the assigned wheel tyre thickness is read out of the characteristic diagram and/or is determined by means of the computing operation and is available as a wheel tyre thickness measurement signal for further use.