Temperature grades represent a tire's resistance to heat and its ability to dissipate heat when tested under controlled laboratory test conditions. The grades from highest to lowest are "A","B" and "C". The grade "C" corresponds to the minimum performance required by federal safety standards. Therefore, the "A" tire is the coolest running. However, even though the "C" tire runs hottest of the three grades, that does not mean it is unsafe. The temperature grade is established for a tire that is properly inflated and not overloaded.