Abstract: Many studies have shown that the impacts of nonlinear factors on the actual mechanical properties of an inerter can't be ignored. In order to investigate the inerter nonlinearities and their influence on ISD (inerter-spring-damper) suspension performance, the ball-screw inerter was chosen as the study object. A nonlinear mechanics model with friction in a ball-screw pair and an elastic effect of screw was built based on the mechanism of nonlinear factors on the force flow process of the inerter. The mechanical property testing of the inerter was carried out using a CNC hydraulic servo exciting test-platform, and the test results truly reflected the impact of friction on the mechanical properties of the inerter. At the same time, it could be determined by the test results that the amplitude of friction didn't vary with the change of inertance, and that the amplitude of friction could be determined to be 60N. On this basis, the friction was removed from the output force of the inerter and the output force model of an inerter without friction was built. The transfer function between the output force of the inerter and the relative acceleration between the two ends of the inerter was established. After discretization of the transfer function and derivation of the least squares format of the system, the parameters of the model were identified through the recursive least squares algorithm. The inertance obtained by the identification was very close to the actual value, which fully vindicated the identification results. According to the identification results, the equivalent stiffness and damping of the screw were respectively determined to be 1270 and 4100 Ns/m. The mathematical model of ISD suspension with a nonlinear inerter was built and the performance of four different structures of ISD suspension was analyzed and compared by Matlab/Simulink and vehicle vibration models with two axles. It was shown from the simulated results that the RMS of body vertical acceleration and body pitch acceleration of a three-element parallel ISD suspension were respectively increased by 9.03% and 9.33%, the RMS of body vertical acceleration and body pitch acceleration of a two-stage series ISD suspension were respectively increased by 3.81% and 4.68%. In addition, compared with a three-element parallel ISD suspension, a two-stage series ISD suspension had better performance, the RMS of body vertical acceleration, body pitch acceleration and tire dynamic load were respectively reduced by 36.2%, 40.7% and 33.5%. In summary, the vibration isolation performance of an ISD suspension was degraded to some extent by considering inerter nonlinearities, but the maximum degradation was no more than 10%, and the impact of inerter nonlinearities on the performance of a two-stage series ISD suspension was less than that of a three-element parallel ISD suspension. The conclusion provides an important reference for the influence evaluation of inerter nonlinearity on an ISD suspension performance and the structure selection of an ISD suspension.