A series of tire property tests have been performed at CALSPAN on the flat bed tire test machine. The tires used in the testing were inflated tires with the tread removed. Identical make/model/size tires in normal (tread not removed) condition were also tested. Three passenger car tires and one truck tire were tested. The purpose of this paper is to present comparative results of the testing and data analysis. The test results objectively demonstrate substantial differences in cornering properties. Grouping all tires together, the measured cornering stiffness of a modified tire was reduced on average to 36.1 percent of the normal tire measured properties (ranging from 24.1 to 49.4 percent; standard deviation was 7.7 percent). Overall the character of the modified tire cornering stiffness plots and other modified tire properties were demonstrated to be markedly changed.