The numerator represents the static weight on the front axle, due to the weight of the van diminished by the vertical load of the trailer on the hitch (the hitch load decreases the front axle load, and hence the grade ability). The second term in the denominator reflects the effect of longitudinal transfer of load from the front axle on a grade due to the elevated position of the CG on the van. The terms in parentheses in the denominator represent the effects of the trailer. The first term in parentheses is the direct effect ofthe added weight of the trailer. The next term arises from the longitudinal transfer of load off of the front axle due to the towing force at the hitch. The last term is the effect of the change in vertical load on the hitch due to the tow force.