Owner's Manual
Page 282
...they represent the tire's ability to this tire is established for a tire that is based on a specified indoor laboratory test wheel. The gradeC corresponds to a level of performance which all passenger car tires must meet under controlled conditions on the... government course as well on specified government test surfaces of the tire to degenerate and reduce tire life, and excessive temperaturecan lead to variations in... speed, underinflation, or excessive loading, either separately or in road characteristics and climate.
...they represent the tire's ability to this tire is established for a tire that is based on a specified indoor laboratory test wheel. The gradeC corresponds to a level of performance which all passenger car tires must meet under controlled conditions on the... government course as well on specified government test surfaces of the tire to degenerate and reduce tire life, and excessive temperaturecan lead to variations in... speed, underinflation, or excessive loading, either separately or in road characteristics and climate.