## 1 Introduction  
The reduction in the number of road accidents and, in particular, their serious consequences is one of the European Union's key objectives for improving road safety, as set out in the EU Road Safety Policy Framework 2021-2030 document--Recommendations on Next Steps Towards \"Vision Zero\". We identify two ways to achieve this vision: either by improving the drivers' skills of car control or by improving road safety and cars' autonomy to utilize artificial intelligence (AI). Nevertheless, it is not excluded that the combination of the human factor (portrayed by the driver) and autonomous vehicles on real road traffic can be of great help in a condition that carries a significant risk of collision [1]. Therefore, it is necessary to develop new or to improve existing car control systems [2, 3, 4, 5, 6, 7, 8], with the help of both existing data, and the theories and tools at our disposal, and proceed with the verification and validation of results compared to those obtained experimentally in laboratory conditions. This applied approach results in a rapid development while maintaining financial efficiency, unlike in cases in which fundamental research requires substantial financial resources. However, before any system is put into real operation, it is worth recalling that it must pass a homologation process that is conditional on the satisfactory completion of the experimental tests. It is precisely the testing of prototypes under real conditions for car manufacturers that carries a great risk of damaging the vehicle, or there is a growing risk of espionage from competing manufacturers. Therefore, simulated conditions are increasingly used in prototype testing. This includes testing cars on skid surfaces [9; 10; 11]. The disadvantage of the sliding surfaces is that the adhesive force changes in step, either for all wheels or for the wheels on the same side of the car. As an alternative to surfaces with reduced adhesion, an additional frame can be used to supplement the car. These frames are delivered in the commercial sphere under the designation SkidCar (SC) [12]. The operating principle of the frame is as follows: with the help of two pairs of wheels, SC can transfer part of the weight of the vehicle through these wheels. In this way, a similar reduction in the adhesive force on the wheels [13] is achieved as on the skid surface. By using the variation in the adhesion force on any wheel, it is possible to simulate an oversteer skid, the asymmetry of the adhesion conditions with the longitudinal axis of the vehicle and other boundary situations that can occur in real operation compared to the sliding surfaces. Since SkidCar is designed to teach drivers in the so-called anti-skid schools, it is designed as a solid and durable device wherein weight does not play a significant role. The motivation of this work is to help SkidCar manufacturers to deliver a reliable frame for a given group of cars [14], which is, of course, significantly limited. Thereby, a prototype of an Alternative SkidCar (ASC) [15] has been compiled, with the advantage of possibly being used on an individual vehicle construction, that is to say, an experimental vehicle [16]. The frame has been designed to verify and confer the usability for vehicle stability. During the construction, the frame is made of commonly available materials with which the minimum construction cost is decisive. Since the alternative SkidCar proved very successful during the driving tests, it has been optimized. This research improves the alternative SkidCar design used for the determination of the driving stability of the experimental car in experimental tests. The design and material optimization of the frame can provide an effective device for obtaining more accurate measurement data from experiments than the current design. The initial step of optimization is the design of the structure modification, for the sake of increasing the rigidity and reducing the weight of the frame as a whole.