Fuel consumption, NO and NOx were monitored using on board apparatus during road driving at constant speeds, for a gasoline passenger car with TWC. Exhaust gas concentrations (ppm) of nitrogen oxides were translated into mass emission values (g/km) by methods previously reported [1, 2, 3 and 4]. In addition to standard vehicle configuration, the experiments included driving with studded tyres, trailer, roof-rack and ski-box. Also, the influence of windy conditions was studied.Generally speaking the use of extra equipment, and also higher speed, entailed raised fuel consumption. The NOx emissions, however, did not exhibit a corresponding dependence. Calculated NO2/NOx ratios (v/v) varied between 0.01 and 0.03.