Truck tires are more than “where the rubber meets the road.” Understanding truck tire sizes, tire load ratings, why ply no longer matters, and more is important for today’s fleet managers.

The load index is a number that generally ranges from 75 to 105; the higher the number, the more weight the tire can support. The speed rating is expressed with letters, and there are several.

Speed rating: This letter denotes the maximum sustainable speed and is found directly after the load index. For S-speed-rated tires, it’s 112 mph; for T, 118 mph. Speed ratings for other tires ...