The research revealed that rolling of wheels of misaligned semi-trailers axles is identical to rolling of slip wheels under the influence of lateral forces, which leads to a discrepancy between the rotation and rolling planes of the wheel. As a result, there are additional lateral and longitudinal forces and increased rolling losses, and as a consequence, the tractor-trailer truck performance, in particular, fuel efficiency, deteriorates. Note that even with the same technical condition of the running gear of the truck tractor and the semi-trailer during their manufacture, different degrees of wear of tires, suspension elements of axles of the truck tractor and the semi-trailer can be revealed after a certain period of operation, as the wear rate depends on axle angles, wheel load, lateral forces, tangential forces (traction and braking) and air pressure in tires. In quantitative terms, these factors are not identical for each axle of the tractor-trailer truck. So, if there are different axle angles and different wear rates of the tread, it is possible to speak about changes in the rolling resistance and fuel consumption of the tractor-trailer truck. Thus, in case of misalignment of one semi-trailer axle by 0.57 degrees, the rolling resistance coefficient increases by 12 %; by 1.25 degrees – 17.8 %; by 2.11 degrees – 26.2 %. An increase in the rolling resistance coefficient leads to the growth of fuel consumption. As an example, it was shown that in the highway driving cycle of the tractor-trailer truck, an increase in the rolling resistance coefficient is doubled from 0.01 to 0.02, fuel consumption in the cycle increases by 43 %, and under the three-time change from 0.01 to 0.03 – by 95 %. This necessitates the design and research works aimed at reducing the axle misalignment of semi-trailers and tractors in the process of manufacture and operation