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A tire's maximum load is the most weight the tire is designed to carry. Since a tire's load carrying capacity is related to the tire's size and how much inflation pressure is actually used, maximum loads are rated with the tire inflated to an industry assigned inflation pressure.
Additionally, load ranges are used to separate tires that share the same physical size, but differ in strength due to their internal construction. "Higher" load ranges are used to identify tires that have a stronger internal construction, and therefore can hold more air pressure and carry more weight.
Each load range has a assigned air pressure identified in pounds per square inch (psi) at which the tire's maximum load is rated. Listed below are the air pressures at which maximum load is rated for popular P-metric and LT tires:
|P-Metric Passenger Vehicle Tires|
|Load Ranges||Abbreviated||Max Load Pressure|
|Light Load||(LL)||35 psi (240 kPa)*|
|Standard Load||(SL)||35 psi (240 kPa)*|
|Extra Load||(XL)||41 psi (280 kPa)*|
|*In an effort to internationally harmonize load ratings and ranges, recently introduced and future LL, SL and XL P-Metric sizes will use ISO/Euro-metric maximum load pressures of 36 or 42 psi|
|Euro-Metric Passenger Vehicle Tires|
|Load Ranges||Abbreviated||Max Load Pressure|
|Standard Load||(SL)||36 psi (250 kPa)|
|Extra Load**||(RF) or (XL)||42 psi (290 kPa)|
|**Reinforced and Extra Load nomenclature may be used interchangeably to designate heavy-duty tires|
|LT-Metric and Flotation Light Truck Tires|
|Load Range||Abbreviated||Max Load Pressure|
|Load Range B||(LRB)||35 psi (240 kPa)***|
|Load Range C||(LRC)||50 psi (350 kPa)***|
|Load Range D||(LRD)||65 psi (450 kPa)***|
|Load Range E||(LRE)||80 psi (550 kPa)***|
|Load Range F||(LRF)||95 psi (650 kPa)***|
|***Industry standards specify selected large LT tire sizes be designed with reduced maximum load pressures|
P-metric tires used on passenger cars and station wagons are rated to carry 100% of the load indicated on the tire's sidewall (or listed for the tire in industry load/inflation charts). However, if the same P-metric tires are used on light trucks, (pickup trucks and sport utility vehicles for example), their carrying capacity is reduced to 91% of the load indicated on the tire's sidewall. This reduction in load results in causing light truck vehicle manufacturers to select proportionately larger P-metric sized tires for their vehicles to help offset the forces and loads resulting from a light truck's higher center of gravity and increased possibility of being occasionally "overloaded."
For example, P235/75R15 P-metric sized, standard load tires used on cars and light trucks would be rated to carry the following maximum loads at 35 psi:
|Cars||Full Value||2028 lbs.|
|Light Trucks||9% Reduced Value||1845 lbs.|
Additionally, while a tire's maximum load is the most weight the tire is designed to carry, its load carrying capacity at lower inflation pressures is proportional to how much inflation pressure is used. For example, P235/75R15 P-metric sized, standard load (SL) and extra load (XL) tires used on cars would be rated to carry the following loads at the inflation pressures indicated:
|Air Pressure (psi)||20||23||26||29||32||35||38||41|
Note: 35 psi is the assigned "maximum load" pressure for standard load tires and 41 psi is the assigned "maximum load" pressure for extra load tires.
The above chart correctly shows that an extra load tire is not rated to carry any more load than a standard load tire when both are inflated to the same pressure (up to the standard load tire's "maximum load" pressure of 35 psi). This is because a tire's load capacity is a function of its size (which determines the size of the "air chamber"), its construction (which determines how much pressure can be held) and the actual air pressure used (which determines how many air molecules are forced inside the chamber). All tires with equivalent physical dimensions carry equivalent loads (until they reach their maximum load pressure).
The tire's maximum load is indicated in relatively small sized print branded near the tire's bead (adjacent to the wheel) indicating the appropriate value. Because tires are global products, their maximum load capacity is branded on the tire in kilograms (kg) and pounds (lb). These values can also be found in the industry's tire load & inflation charts.
NOTE: P-metric and Euro-metric sized tires' "maximum load" inflation pressure may be, and often are, different that the tire's "maximum inflation pressure."
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