the usual form of coupling connecting the tractor and trailer units of an articulated vehicle combination permits an increasing amount of trailer roll as the articulation angle increases, a defect which can be avoided by inverting the coupling. tests have been carried out to assess the benefits from this modification in the case of road tankers of relatively stable design (low centre of gravity). in the tests the speed at which the vehicles negotiated s-shaped curves was gradually increased until either the vehicle could go no faster or it became unstable in roll. with the normal coupling, unstable roll arose at a centrifugal acceleration in the region of 0.41-0.42g. with the inverted coupling unstable roll had not developed at 0.44g. the highest centrifugal acceleration achieved (a limit set by the power of the vehicle). the advantage from inverting the coupling would be expected to increase as the height of the centre of gravity of the loaded tanker is increased. (a)

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