Tire operating temperature is of vital concern to tire engineers because it relates to both service life and power loss in a tire. It may also affect performance in areas such as traction and cornering ability. Operating temperature is a limiting factor in the choice of construction material for truck tires, which run at much higher temperatures than do automobile tires. Adhesion failures are generally believed to be caused by excessive heat. Yet White was unable to produce separation by heat alone, even though he held a tire at 300° F for two hours, then tried to pull the components apart. In high speed operations the high temperature developed may weaken the ply bonds in a tire, which can then be separated by a combination of centrifugal force and fatigue. If the temperature reaches 350 to 400° F, however, tire separations will occur before fatigue type failures are evident. In fact, a rough relationship has been established between attained tire temperature and the type of failure in road tests. Failures more directly related to fatigue are also hastened by high temperatures. Natural rubber softens or reverts, while SBR tends to harden and become brittle under the same conditions. With the exception of groove cracking a typical fatigue failure starts from an inhomogeneity as a small internal crack and grows by heat and mechanical action. The torn surfaces usually rub against each other to cause heat degradation. In this case heat is the result rather than the cause of failure. Tread sections lying at the side of superhighways are evidence that the tires from which they came were overworked. Temperature build-up restricts use of thicker treads, of longer wearing high-grip tread compounds, and the speed potential of any tire. Tread wear is sharply reduced by an increase in temperature, whether ambient or work-induced. So many tire properties are adversely affected by high temperature that heat has been called the great enemy of tires. The two principal purposes of this review are to examine some of the causes and results of tire temperature build-up and to discuss some of the methods which have been used to measure or compute temperatures in various tire regions.