## 6 Results of Research and Discussion  
In order to estimate the vibration characteristics of the cars, a previously described mathematical model was applied. The calculations of the displacement and acceleration of both the sprung and unsprung masses were performed. With the aim of comparing suspension characteristics during technical inspections of vehicles (which are supposed to be diagnostic in character), a simplified model was chosen. The parameters characterizing both vehicles selected for comparison were used for the calculations. Therefore, the first vehicle (vehicle 1) was fitted with standard equipment that conformed to the specifications of the manufacturer, as described earlier. Shock absorbers with sport-like damping characteristics were mounted on the second vehicle (vehicle 2). Calculations were made for the wheel vibrations of the vehicles corresponding to the operation of a vibration exciter control device for car shock absorbers at a frequency of 25 Hz and an amplitude of 6 mm. The results obtained from the calculations were juxtaposed graphically for each vehicle in Figures 7-10. Figure 8: Sprung mass displacement characteristics for different values of stiffness obtained from calculations. Figure 7: Unsprung mass displacement: characteristics for different values of stiffness obtained from calculations. In the case of unsprung mass for both vehicles, we observed that both displacement and acceleration had the same pattern. This was understandable due to the identical conditions of movement excitation applied to the wheels of both vehicles. As can be seen from the juxtapositions, damping changes resulting from modification of the suspension components were visibly evident in the case of unsprung mass vibrations. For resonant frequency, i.e., about 12 Hz, the acceleration of the unsprung mass was more than 0.6 m/s\({}^{2}\) higher for the vehicle with a modified sport suspension. In the case of this modified suspension, the displacement of the sprung mass was also higher, and the differences increased with decrease in the vibration frequency. At low frequencies, which are responsible for discomfort resulting in travel sickness, the differences could be almost three times higher. Vibrations experienced by vehicle users can be divided into two main categories. The first category includes vibrations classified as general vibrations, which have an impact on humans through the lower limbs, pelvis, and back. Local vibrations, which have an impact on humans through the upper limbs, belong to the second category. The vibrations on the driver's seat and on the steering wheel were analyzed. Acceleration measurements of the vehicles during the entire test are presented in Figure 11. As shown, in the phase of exciting vibrations, the observed accelerations had values higher by 30% for vehicle 2. In addition, as can be seen in the second phase of the test, in the case of vehicle 2 there was a decrease in these values related to the damping of vibrations. The comparison of the obtained results highlights the differences in the suspension characteristics of the tested vehicles. Figure 10: Sprung mass acceleration: characteristics for different values of stiffness obtained from calculations. Figure 9: Unsprung mass acceleration: characteristics for different values of stiffness obtained from calculations. Vertical acceleration measurements of the driver's seat surface are presented in Figure 12. As shown, the maximum values recorded during the whole test differed by more than 100%. The differences were most clearly visible in the phase of exciting vibrations, as well as in the final phase of the test, when we observed fading vibrations. Following the immobilization of the exciter plate, the differences could be seen. Analogous dependents could be indicated in the case of vibrations observed for the steering wheels, as shown in Figure 13. Here, the noticed differences were smaller. The maximum acceleration values registered during testing for the vehicle with standard shock absorbers reached 2.5 m/s\({}^{2}\).