Internal combustion engine lubrication is essential for unwanted energy and material losses. As part of the experimental work, the lubricity of both new and worn motor oils of Society of Automotive Engineers (SAE) 15W-40 and SAE 10W-40 with different American Petroleum Institute (API) performance classifications, which were taken from various motor trains during maintenance or oil change, was assessed. A total of sixteen lubricant samples were evaluated. Lubricity, i.e., the load capacity of the lubricating film, was evaluated on the basis of the Reichert test. Viscosity, as one of the most important parameters of lubricants, was evaluated by the Stabinger Viscometer. Chemical degradation of motor oils (oxidation, nitration, sulfation), contamination of oils with fuel, soot, water, and loss of antioxidant zinc dialkyldithiophosphate (ZDDP) were monitored by Fourier-transform infrared (FTIR) spectroscopy. Of the fresh motor oils, OMV 10W-40 API SL/CF motor oil had the best lubricity. URANIA LD 15W-40 API CI-4 and M7ADS V 15W-40 API CI-4 CH-4/SL oils showed similar lubricity. M7ADS III 15W-40 API CF-4/SG motor oil showed the highest wear of wear surface, i.e., the lowest lubricity, of the tested new motor oils. Correlation analysis of the experimental data confirmed that the fuel content penetrated the motor oils significantly negatively correlates with the viscosity (R = −0.87). The low water contamination in motor oil does not cause a significant negative effect on lubricity. A significant correlation between the oxidation, nitration, and sulfation products of chemical degradation of the tested oils was confirmed (R ≥ 0.90). These degradation products improve lubricity due to their polarity, i.e., they have caused better lubricity of worn oils compared to new motor oils. Even the depletion of the antioxidant ZDDP did not affect the reduction in lubricity and anti-abrasion properties of chemically degraded motor oils. The experimental results of testing of worn motor oils taken from motor trains showed that current motor oils have excellent lubricity, which they maintain throughout their life.

Bringing the car into a skid is realised by the adhesion force decrease. This can be reached either by a coefficient of adhesion decrease or decrease of a radial reaction on the vehicle's wheel. For the purpose to the vehicle's behaviour change according to stability we chose the way of radial reaction change. To decrease the adhesion force transferred by the vehicle's wheels, the required part of radial reaction of a particular vehicle's wheel was transferred to the road, out of the vehicle's wheels, using additional auxiliary wheels. The auxiliary wheel units are connected to suspension arms. The article contains individual currently used ways for the adhesion force change and the unique way in the form of the system SlideWheel designed by the authors. The system SlideWheel, which was designed by the authors of this article, consists of three circuits. The first circuit is the mechanical part of the wheel unit, the second one is designed in the form of a hydraulic system and the third circuit is an electrical system used to control the wheel unit's lift through the hydraulic system. The system was designed to be used for experimental measurement purposes in education in order to experimentally simulate oversteer or understeer of the vehicle. The real measured data from a particular drive test are stated and evaluated in the conclusion. The measurement is implemented on a special experimental vehicle equipped with the SlideWheel system. Based on the experimental measurements, we have come to the conclusion that using the SW system, it is possible to change the adhesion force of a road vehicle.The paper deals with a new system for radial reaction change of vehicle wheels. This system has minimal added weight to the vehicle. At the same time, none of the components exceeds the ground plan of the vehicle. With the newly created system, it is possible to reduce radial reactions on any car wheel. The measured results are consistent with the vehicle's ride on sliding surfaces.

The article presents the results of simulations using the finite element method (FEM) aimed at examining the extent of damage to the wheel rim as a result of hitting an obstacle. The obtained results can be used as comparative data during the performance of expert opinions to give an answer as to how the damage occurred. The data obtained from the FEM simulation can also be used in the process of geometric optimization of the rim, which aims to obtain a rim resistant to this type of damage.

This paper deals with the optimization of the crossbars, parts of the existing frame of the experimental system of the Alternative SkidCar. This part plays a crucial role and is designed to enable and ensure reduced adhesion conditions between the vehicle and the road. To this end, its optimization targeted here is performed using both analytical calculations and simulations in MSC Adams software, wherein the loading forces and boundary conditions on the frame support wheels are obtained considering the static conditions, as well as the change of the direction of travel. The least favourable load observed was used, later on, as the input value for the strength analysis of the frame. The analysis was performed using the finite element method (FEM) in SolidWorks. Based on the linear and nonlinear analyses performed, the course of stress on the frame arms and critical points with the highest stress concentration were determined. Subsequently, according to the results obtained, a new design for the current frame was proposed and, thereby, warrants greater rigidity, stability and strength to the entire structure, while reducing its weight and maximizing the potential of the selected material. The benefit of the current contribution lies in the optimization of the current frame shape, in terms of the position of weld joints, the location of the reinforcements and the thickness of the material used.

The article deals with various ways of bringing a car to the stability limit in terms of adhesion conditions. The article deals with the possibilities how to reduce the adhesion force transmitted between the car wheels and the road. Subsequently, we evaluate the change in the behaviour of the car depending on the way the adhesion force changes. The measurement is carried out on a special experimental vehicle. The aim of the article is to find the differences in the car behaviour when inducing a limit situation. In the first case, by reducing the coefficient of adhesion and, in the second case, by reducing the radial response on the car wheels. The change of the coefficient of adhesion is done by means of a sliding surface (foil) sprayed with water. To reduce the radial response on vehicle wheels, we used a device called Alternative SkidCar. It is similar to a commercially available SkidCar device that is built for a particular experimental vehicle.The car behaviour in both cases was verified on the basis of driving tests in a direct direction. The actual test was carried out in the form of critical braking. Initial set of measurements was realized for dry road and separate vehicle. Subsequently, we proceeded to the experiment on the sliding surface. The coefficient of adhesion is reduced to a constant value on the sliding surface. The last set of experimental tests was performed with the help of Alternative SkidCar. We carried out the initial measurements for a situation where the car wheels transmitted a full radial response. In this way we found out to what extent the frame of the Alternative SkidCar influences the car behaviour. Furthermore, we reduced the radial response of vehicle wheels in three stages. Subsequently, we processed the measured values and, by comparison, we found differences from comparable tests. Due to the reduced adhesion force, a limit state in relation to stability at lower speeds can be induced on the vehicle. In this way, it is possible to achieve skid at a lower, so-called safe speed.