## 1 Introduction  
The exploitation environment of equipment designed for use in special conditions (e.g., forestry industry, power industry, mining industry, or the military) is changing rapidly due to, among other things, the availability of new technologies, the need to ensure higher comfort of work, and the need to meet new emission limitations. Currently-produced engineering objects are energy efficient, comfortable, relatively easy to use and eco-friendly. However, implementation of new solutions to such objects often results in higher purchase costs. Unit maintenance cost can be balanced by sufficiently efficient and failure-free operation of such objects, which is the effect of appropriate training of the operator and the suitability of the technical parameters of the object to the local conditions of use. Another way to improve efficiency ratings is to modernize existing equipment. New and modernized equipment is expected to be of consistently high quality and sufficiently long service life. This is evident in many industries, including special high-mobility wheeled vehicles designed for off-road use. With regard to vehicles manufactured in the 1970s and 1980s, their operation potential was planned for 30 years and the mileage for 200-250 thousand kilometers. However, at present, these expectations are changing in the direction of increasing the mileage to 500-600 thousand kilometers and decreasing the service life to 20 years [1]. The verification of assumptions about the maintenance profile demands appropriate changes in the field of vehicle production and in its equipment, with newer systems supporting the work of crews, e.g., [2, 3, 4], as well as in the testing and verification of operating parameters [5]. Invariably, great difficulties appear when evaluating the durability of such vehicles with respect to the target mileage [6,7]. Analysis and verification of the durability of a new vehicle is carried out in several stages, most often in accordance with the adopted design model, e.g., shown in Figure 1[8]. Three basic stages of the verification of design assumptions can be distinguished: analysis of computational models and virtual tests carried out with the use of dedicated computer software (Final Element Method--FEM, Multibody Dynamic Simulation--MBDS) [9,10]; stand tests of subassemblies and, if possible, of all vehicles [11,12]; and prototype tests of qualification mileage in normal and contract research conditions on proving grounds and test road sections [13]. The dynamic development of computers and software has caused vehicle manufacturers to increase the share of virtual testing in the process of preparing vehicle designs for serial manufacturing, allowing for the abandonment (or limiting) of physical testing of the prototype [14]. Significant progress has been attained in the use of test rig examination of subassemblies and vehicle systems over the last 20 years, and even of whole vehicles within the last 10 years. Examples of test rigs for carrying out vehicle durability tests by generating vertical excitations from the road profile (tire-coupled road simulator) and placing the vehicle in a complex load state (spindle-coupled road simulator) are shown in Figure 2.  
These tests usually concern the engine and drivetrain, steering, frame, cab, seats, suspension, hydraulics, and controls. However, the performance of such tests requires the establishment of test stand control signals (obtained by the compilation of the recorded road load data acquisition--RLDA) [5,15,16,17] and the satisfaction of the test stand requirements, which limit the possibility of testing vehicles with 6 \(\times\) 6 or larger chassis and over 6000 kg GVW [11]. Moreover, such stands are very expensive; for this reason, they are used by  
Figure 1: A model of the system design process based on a NASA V model [8]. Figure 2: Tire-coupled road simulator (**left**) and spindle-coupled road simulator (**right**) [11]. the largest vehicle manufacturers [18].