Nowadays special tensometric wheel pairs are used for the wheel - rail system monitoring. In this work the task of unification of the tensometric wheel pairs and reducing of the expenses required for testing is considered. The equipment allowing realization of the measurements for the monitoring of wagon or locomotive system wheel–railing using ordinary standard wheel pair is elaborated. The objective of optimization is to find the shape of the equipment’s mounting disk with minimal weight constrained by specified displacement and stress levels. Dynamic excitations due to the rail irregularities and flat of wheel are taken into account. The strength calculations of the mounting disk are realized by FEM and are relatively time consuming. The conventional topological optimization as well as shape optimization using metamodels is discussed. Procedures of metamodel building by global and local approximations, as well as kriging are discussed in detail. The optimal curved shape of the cross-section of the ellipsoidal mounting disc is elaborated.