Light Truck Tire Load Index: LT vs P Metric Numbers

LT and P metric tires are different classes

A light truck (LT) tire is defined by federal regulation as a tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles. A passenger car tire is a tire intended for use on passenger cars, multipurpose passenger vehicles, and trucks that have a gross vehicle weight rating (GVWR) of 10,000 pounds or less. This distinction matters because the two tire classes are engineered with different load capacities and inflation pressures. For a deeper look at how load ranges differ, see tire load range for light trucks.

P metric tires, such as P245/70R17, are built for passenger cars and crossover SUVs. LT tires, such as LT245/70R17, are built for pickups, vans, and heavy SUVs. The load index on the sidewall is a numerical code that corresponds to a specific load carrying capacity, but the meaning of that number depends on the tire class and the inflation pressure it is rated for. LT tires generally require higher inflation pressures to achieve their rated load, and they often use load range letters (C, D, E, F) instead of a single load index. To compare the two construction types, check P metric vs LT tires.

How load index works

The load index is part of the tire service description, for example 115/113R. It tells you the maximum load a tire can carry at its maximum rated inflation pressure. However, the load index alone does not tell you the tire's load range, which describes the ply rating and the corresponding maximum inflation pressure. For LT tires, load range is a more meaningful comparison because it directly relates to the tire's structural strength. Learn more about reading the tire service description and how load index and inflation interact.

When comparing P metric and LT tires of the same physical size, the LT version will usually have a higher load index and a higher maximum inflation pressure. Federal standards limit the maximum permissible inflation pressure for passenger car tires to a set of values, while LT tires are subject to a different standard and can be inflated to higher pressures. Always check the sidewall for both the load index and the load range, and verify that the combined load rating of the tires on an axle meets or exceeds the vehicle's gross axle weight rating.

• Load index: a number that corresponds to a specific maximum load capacity.
• Load range: a letter (C, D, E, F) that indicates the ply rating and maximum inflation pressure.
• Inflation pressure: the load rating is only valid at the stated cold inflation pressure.

What the federal standards say

Federal Motor Vehicle Safety Standard 571.110 defines both light truck tires and passenger car tires, and it applies to vehicles with a GVWR of 10,000 pounds or less. Standard 571.139 covers new pneumatic radial tires for light vehicles, and it clarifies that light truck tires with a tread depth of 18/32 inch or greater are subject to the more demanding requirements of Standard 571.119, which also applies to tires for vehicles with a GVWR over 10,000 pounds.

If you install a passenger car tire on a truck, the load rating must be derated. Under Standard 571.120, for a multipurpose passenger vehicle, truck, bus, or trailer, a passenger car tire's load rating is divided by 1.10 before comparing it to the gross axle weight rating. This 10% reduction accounts for the higher loads and inflation requirements of truck applications. In practice, this means a P metric tire may be acceptable for light-duty pickups or vans when the vehicle is not heavily loaded, but for frequent towing or hauling, an LT tire is the more robust choice. For more on towing loads, see tire load range for towing.

The load rating definitions in the federal standards are consistent: load rating is the maximum load a tire is rated to carry at a given inflation pressure, and maximum load rating is the rating at the maximum permissible inflation pressure. LT tires are designed to operate at higher loads and higher inflation pressures than standard passenger tires, which is why they are commonly recommended for work trucks and camper vans.

Picking for your pickup or van

The decision between LT and P metric tires depends on how you use your vehicle. If you only carry passengers and light cargo, a P metric tire with an appropriate load index may be sufficient, especially if the vehicle manufacturer recommends it. But if you regularly tow trailers, carry heavy loads, or drive on rough roads, LT tires offer a higher safety margin because they are built to handle higher inflation pressures and heavier loads. Explore our best light truck tires and best all-terrain tires for options.

When selecting tires, check the vehicle's placard and owner's manual for the original equipment size and load rating. The sum of the maximum load ratings of the tires on an axle must be at least equal to the gross axle weight rating. For a light truck, that calculation uses the LT tire's rated load at the recommended inflation pressure. For a P metric tire, you must apply the 10% derating before comparing.

For most half-ton pickups and full-size vans, an LT tire with a load range C or D is a good middle ground. For heavy-duty models, load range E or F is common. Do not exceed the rim's rated capacity when choosing a tire. For a popular LT size, see our best LT265/70R17 tires comparison.

What to pick for your use

Questions

Can I use P metric tires on my light truck?

Yes, but federal rules require reducing the load rating by 10% when a P metric tire is installed on a truck. Check that the derated capacity meets your axle's gross axle weight rating and your actual loads. For more, see P metric vs LT tires.

What is the difference between load index and load range?

Load index is a numeric code that corresponds to a specific load capacity at a given inflation pressure. Load range is a letter that indicates the ply rating and the maximum inflation pressure; it is a better guide for comparing LT tires. Learn more about LT load ranges.

Do LT tires require higher inflation pressures?

Yes, LT tires are designed to operate at higher inflation pressures to carry heavier loads. Always use the vehicle manufacturer's recommended pressure for the specific tire, not the maximum printed on the sidewall. See tire pressure basics.

How do I know which load range I need?

Start with the vehicle placard and the gross axle weight rating. Estimate your maximum axle loads when fully loaded, then choose a tire whose rated load at the recommended pressure meets or exceeds that number. For regular towing or heavy cargo, choose a higher load range. Check load range for towing.