Load / Ply Ratings
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The load range or ply rating indicated on a
tire's sidewall helps identify its strength and ability to contain air
pressure. Load ranges are identified in ascending alphabetical order for
trailer tires (the further along the letter is in the alphabet, the
stronger the tire and the greater amount of air pressure it can withstand
and load it can carry). Before load ranges were adopted, ply ratings were
used to identify the relative strength of trailer tires with higher
numerical values assigned to tires featuring stronger, heavier duty
constructions.
Today's load range/ply ratings do not count the actual number of body ply layers found inside the tire, but indicate an equivalent strength based on early bias ply tires. Most radial tires have one or two body plies, and trailer tires, even those with heavy duty ratings (10-, 12- or 14-ply rated), actually have only two or three fabric body plies, or one steel ply. |