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Torsional stiffness is important parameter of chassis that affect the handling performance of chassis. Torsional stiffness can be determined using Finite Element Method (FEM) in early stage design of its. In order to validate the FEM result, experimental work needs to be done. The fixture has been design in simpler stucture, flexible for any kind of chassis and using a simple measurement’s equipment such as dial indicator and load cell. Twist fixture has been designed for measuring of torsional stiffness of TATA cab chassis indirectly. The fixture measured the deflection caused by torsion subjected to the chassis. The torsional stiffness was calculated based on measured displacement of chassis. The result of comparison shows that the experimental results in agreement with the simulation results. Therefore, the simulation results of TATA cab chassis model are valid.

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This thesis deals with a study on the torsional stiffness of existing truck chassis and some others improved models by using finite element method. The objective of this study is to improve the torsional stiffness by design and to provide simulation of the deflection on the chassis. The problem on the chassis is the deflection on the chassis whereas higher displacement will affect the torsional stiffness of the truck. ABAQUS was used as it is a powerful engineering simulation tool based on the finite element method. The magnitude of torsional stiffness for existing and modified models were calculated based on data of deflection of each models which were obtained from the finite element simulation. The multi holes model was choosen as the best proposed model due to the highest of torsional stffness as comparison result among existing and modified models.Keywords: torsional stiffness, finite element method, truck chassis 1.Introduction Transportation industry plays a major role in the economy of modern industrialized and developing countries. The predominant goal for the design of a commercial vehicle for the economy during its use from acquisition until disposal (minimal life cycle), and it is important to know that more than ¾ of the cost do not include the purchase. However requirement of safety, handling and ride comfort are also to be satisfied. It is universally recognized that torsional stiffness is one of the most important properties of a vehicle chassis. This is a measure of the stiffness of a frame or chassis in twist. When driving on uneven road surfaces, the chassis frame is exposed to large torsional forces. The front section behind the cab is torsionally flexible, while the rear section at the rear axle or bogie is torsionally rigid. This torsional flexibility provides the chassis with good mobility at the same time as ensuring adequate strength. This term can be obtained by measurement or by computer simulation.Many researchers carried out study on truck chassis. O'Neal Arant. M [1] had conducted study on effected of chassis torsional stiffness on the accuracy of the heavy vehicle. The aim of the study is to represent all the trailer models to extreme ends of the range of chassis torsional stiffness. The primary goal of the analysis was to assess the accuracy of rollover simulations, sublimit under-steer test were also performed to assess the sensitivity of vehicle simulation result to chassis flexibility. According to Michael O'Neal result, it clearly shows that the torsional flexibility of the chassis can significantly affect the accuracy of vehicle dynamics.Another case study was presented by Sampo et.al [2], they analyze the chassis torsional stiffness that influence the vehicle dynamic. The objective of the paper is to introduce two analytical vehicle model that constitute an efficient tool for a correct evaluation of the main effect of the chassis torsional stiffness on vehicle dynamic. The modal takes account of chassis torsional stiffness for the evaluation of the lateral load trans...