Abstract One of the outstanding weaknesses of GR-S rubber in tire-tread formulations is a pronounced tendency to crack in road service. In general cracks originate at the bottom of cuts or of moulded grooves in the tread, but spontaneous cracking may originate from local weak spots in the interior of the tread. Properly formulated natural rubber stocks are not susceptible to this type of failure, and usual laboratory and plant criteria and test methods developed by long experience for natural rubber formulations have been proved inadequate and misleading with respect to the evaluation of the susceptibility of GR-S rubber to this type of failure. These considerations have led to the development of the compression-tear test for susceptibility to cut growth which is the subject of this paper. The underlying principle of the test is to develop, under static easily controlled laboratory conditions, the type of strain which is the normal resultant of impact shocks of indeterminate severity under road service conditions. When pressure is applied at the surface of a cut or groove in a tire tread, the usual result is to pinch the walls of the cut together at the surface and to force them apart midway of the cut, thus producing a shearing force on the rubber under compression at the bottom of the cut. The U. G. I. compression-tear test is designed to set up a shearing force under conditions of high compression at elevated temperatures at the bottom of a standardized cut, and to measure the rate of cut growth with time.