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Torsional stiffness of the car’s body is an important parameter used when creating the technical design of the car. It plays an important role in both passive and active safety of the car. Driving characteristics of the car going through a corner depend among others on the distribution of vertical load of individual wheels. Distribution of vertical load is closely connected with the car’s body roll. If the body’s torsional stiffness is low, then its torsion can influence the wheel vertical loads in a different way compared with loads that were to be achieved by original design. However, as changes of shapes during torsional twist are very small, it is difficult to measure the deformation by common mechanical systems.
The car’s body deformation is measured by optical scanners Tritop and ATOS available in the Institute of Automotive Engineering laboratory. Position of reference points are measured when different torque levels are applied. These points are then used to calculate the deformation.
In order to calculate torsional stiffness, applied torque must be determined using strain gauge scales that analyze reactions occurring under the wheels. This torque is induced by lifting one part of the car. Other parameters that have to be known include deformation (torsion angle) that is obtained by TRITOP from the change of measured position of the points placed on the car’s body during each applied torque level..
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