A tire's temperature grade indicates how well the tire can dissipate heat under test conditions, assuming proper inflation and maintenance of the tire.  There are three possible traction grades: A, B, and C.  A rating of A is the highest possible temperature grade, while C is the lowest. 

 

Temperature grades are determined in a controlled test environment, where the tire repeatedly undergoes speed tests until it is destroyed.  Depending on how long the tire endures these tests, a temperature grade is assigned.  A temperature grade of C indicates that the tire meets minimum standards set by the U.S. government.