Before revision: The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is: D (kN) = 9.81 x (Gross Vehicle Mass X Gross Trailer Mass )/( Gross Combination Mass).
After revision: The corresponding formula for a truck and trailer combination, used to determine the required D-value of a coupling, is: D (kN) = g x ((0.6 x T x R )/( T = Weight of towing vehicle including the vertical load on the fifth wheelR = Total weight of the loaded semi-trailerU = Vertical load on the fifth wheelg = Acceleration due to gravity (assumed to be 9.81 m/s 2 )