This paper presents selected results from a full-scale test program aimed at development and validation of test procedures for evaluating car/trailer handling and braking performance. The results described herein pertain to the observed effects of hitch load, load leveling (via weight distributing type hitches), and tow car tire inflation on modifying the tow vehicle understeer gradient and its sensitivity to lateral acceleration. Abrupt reductions in understeer were observed which increased the tendency for jackknife. Front/rear tire pressure differentials (front lower than rear) have a significant beneficial influence when the hitch load is high. Effects of these hookup variables on trailer swing mode stability and combination vehicle stopping distance are also presented.