Ply Rating and Load Range
Ply ratings identify the load carrying capabilities of a tire in terms of plies. Ply rating originally referred to the number of cotton layers used to strengthen a tire's casing. Today, when tires are labeled 10-ply, they are not actually constructed of 10 individual layers of cotton, but offer the equivalent strength. Passenger tires are currently constructed from one or two body plies, while light truck tires consist of two to three, or one steel ply. Over time, steel ply and radial construction replaced cotton leading to a new distinction, load range.
Load range identifies the maximum amount of weight that can be placed on a tire horizontally, which varies depending on tire size and inflation limits.
- Load Range
- Ply Rating
Passenger tires are assigned numeric load ranges that correlate with the amount of weight the tire can accept. Most passenger tires are rated Standard Load P-Metric and feature either no indication on the sidewall or are branded 'Standard Load". Passenger Tires rated Light Load P=metric are labeled 'Light Load," and feature "LL" in their description (P285/35R19 LL). Extra Load P-metric passenger tires are branded as "Extra Load" and are labeled with an "XL" in their description (P235/75R-16 XL).
The Euro-metric system is similar to the P-metric system except in terms of load carrying capacity. Standard Euro-metric tires feature no sidewall load range indication. With Extra Load and Reinforced Euro-metirc tires, each tire's sidewall is branded and identified with "XL" or "RF" in its description (295/50R20 XL).
Light Truck Tires
Unlike passenger tires, light truck tires are labeled in ascending alphabetical order. The further the letter is located alphabetically, the greater the tire's strength and air capacity. LT Metric, Flotation and Numeric tires are branded with their load range ("Load Range B" or "LRB") or ply rating (6" Ply Rated") on their sidewalls and feature load range letters in their descriptions (LT235/75R-16B).
ST-metric tires have different load ranges and inflation ratings than cars or light trucks but have the same basic metric sizing. ST-metric special trailer service tires have an "ST" prefix in front of the size (ST235/80R16) and their load range is branded on their sidewalls.