Fiat 500L 2015 Owner's Manual page 424

422 IF YOU NEED CONSUMER ASSISTANCE
The grade C corresponds to a level of performance,
which all passenger car tires must meet under the Federal
Motor Vehicle Safety Standard No. 109. Grades B and A
represent higher levels of performance on the laboratory
test wheel, than the minimum required by law.
WARNING!
The temperature grade for this tire is established for
a tire that is properly inflated and not overloaded.
Excessive speed, under-inflation, or excessive load-
ing, either separately or in combination, can cause
heat buildup and possible tire failure.