## 1 Introduction  
Due to its simpler structure and lower manufacture/service cost, Macpherson suspension with the functions of vibration isolation and steering has been widely used in light mining trucks [1; 2; 3; 4; 5]. The steering arm is a key component in the steering mechanism integrated with Macpherson suspension, and its strength is very important for the security and reliability of the trucks. However, recently it has been frequently fractured in a kind of mining truck, which seriously threatened the driver's security and caused the damage to property. Generally, a complete design process for a steering arm or other similar parts is as follows [7; 8; 9; 10; 11; 12]. First, a full vehicle model, also called a virtual prototype model, is established based on multi-body dynamical software such as Adams, RecurDyn, SIMPACK, and so on. Second, forces on the steering arm are obtained under different roads and manipulation conditions, according to the established model. Third, the forces, particularly those under extreme conditions, will be used to optimize the geometry or shape of the steering arm considering the motion interference by using a professional finite element analysis (FEA) software, such as ANSYS and ABAQUS. This digitized method, which shortens the design cycle and reduces the design cost, has been widely used, compared with the traditional method based on experiments. Surely, the full vehicle model should be comprehensively verified by experiments. However, it is not easy to accurately determine all parts' characteristics, particularly those of the tires and roads in surface mining, although the 3D geometric model of a mining truck can be established according to its engineering drawings. For example, when selected as a tire model in the Adams environment, PAC 2002 has up to 200 parameters that should be determined for a dynamic simulation [13; 14; 15]. For a tire that has not been completely measured by experiments, it is hardly possible to obtain these parameters, which causes a large difficulty in the dynamic simulation. In addition, determining the dynamical parameters of the full vehicle model and verifying its simulation results may spend much time on experiments, which reduces the efficiency of a new replacement part to some extent. Due to the complex characteristics of key parts, road surfaces, and tires, there are many design methods for the strength design, fatigue test, and life prediction of the steering arm according to the theoretical forces or accelerations [16; 17; 18; 19]. In general, these methods did not consider the features of the vehicle, arrangement of each structure, and the assembly which may cause kinematic interference, and then the obtained results are often limited. In fact, the complete design method is beneficial to a company in the long run, but a fast and effective design will be the engineers' emphasis in the short term for the problem that only a few parts are broken in the vehicles. In this current stage, it is urgent to present a fast calculation method which can partly consider the characteristics of the road and tire for improving the steering arm. Therefore, a fast calculation method for improving the steering arm of mining trucks with Macpherson suspension is proposed in this paper. This method can avoid establishing a full vehicle model and only analyse the left steering mechanism, increasing the efficiency of improving the steering arm. In this method, after the force analysis on the tire, the torque on the steering arm is calculated by using the empirical values of the rolling resistance coefficient and friction coefficient allowed to be limited in the two ranges; the rigid-flexible coupling model for the left steering mechanism in ANSYS environment is established and solved to obtain the distribution stress on the steering arm under extreme conditions. Then, the stress test is carried out to verify the reliability of the simulation results based on the fast method.