After pointing out that the operating temperature is a vital factor in the life of a pneumatic truck-tire, the author outlines an investigation that was conducted at the plant of the Goodyear Tire & Rubber Co. This sought to determine (a) the best means of measing tire temperatures; (b) the temperature effect of inflation-pressure, load, long runs, frequency of stops, and the sizes of the rim and the tire; (c) the temperature of various designs of tire; and (d) some suitable means of reducing large-tire temperatures. The main reason for the rise in the temperature of a tire is stated to be the generation of heat resulting from rapid flexing; and the various factors having to do with this generation of heat and its dissipation to the atmosphere are listed.The laboratory testing-machine and the methods and apparatus employed to measure the temperatures are described. One method was to measure the initial temperature and determine the rise by the increased pressure as shown by a gage fastened to the hub. The necessary corrections for air leakage and changes in the volume of the tire during operation were determined; the results are presented graphically. A type of tire thermometer was subsequently designed and used, but this was not satisfactory on account of the great differences between the thermometer readings and the temperatures as calculated by the pressure-volume method.Thermocouples placed inside the tubes were also tried and results that checked fairly well with those calculated by the pressure-volume method were obtained. Also a detachable type of thermocouple was placed in a hole drilled through the tread to the cushion or carcass as desired.The necessity of knowing that the air in the tubes was not saturated required the use of an air separator when inflating the tires. The effects of convection currents inside the tube on the thermocouples and thermometers are discussed. The theory as to the manner in which the temperature of a tire is reduced by using a small quantity of water inside the tube is given and convincing experimental evidence is presented to substantiate this theory.After summarizing his conclusions, the author expresses the belief that the study of pneumatic-tire temperatures is of much greater commercial importance and possibly of greater scientific interest than is generally realized. The rise in the temperature of a tire is a direct and sensitive indication of the waste of energy due to its operation. While this loss cannot be eliminated, it can be reduced by proper selection and combination of materials.