In this paper a pair of two rail-wheels which is submitted to degradation due to the unbalanced vibration and wear during long time running is studied. The pair of wheels works under the minimum allowable value of flange thickness and tread diameter. The thickness of flange and the diameter of wheel tread are dependent on each other by maintenance action, referred as reprofiling in this study. In order to keep the thickness of flange above a given value for the sake of safety, when the thickness of flange decreased, the diameter of the tread will be reduced by reprofiling (rotary cut) so as to increase the thickness of flange.The natural degradation of thickness of flange and the diameter are modelled by Wiener process. The dependence between two wheels is based on the wheel diameter difference. The inspection of the wheels is period and perfect. When the thickness of flange degrades under the given threshold, or when the diameter of anyone of the pair of the wheels degrades under the given threshold, the system is regarded as failed. When the difference of diameters between two rail-wheel pairs is greater than the tolerance or the thickness of the flange reduces over the preventive maintenance threshold, a preventive maintenance activity is planned. Hence the preventive maintenance threshold and the maintenance period are optimized by simulations.