P-Metric vs LT Tires: Car vs Truck Specs

What Are P-Metric and LT Tires?

The U.S. federal regulations draw a clear distinction between passenger car tires and light truck (LT) tires. Under 49 CFR 571.139, a passenger car tire is one intended for use on passenger cars, multipurpose passenger vehicles, and trucks with a gross vehicle weight rating (GVWR) of 10,000 pounds or less. P-metric tires are typically marked with a "P" before the size, such as P225/60R16.

A light truck tire, as defined in 49 CFR 571.110 and 49 CFR 571.119, is a tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles. LT tires use a different size format without the "P" prefix, like LT265/70R17. The distinction matters because the two types are engineered for different loads, pressures, and driving conditions.

While both types can be fitted to a pickup or SUV, the intended use and load capacity differ significantly. Knowing your vehicle's GVWR and axle ratings is the first step in deciding which tire type is appropriate, as explained in tire load range for light trucks.

Load Range and Load Ratings

LT tires are built to carry heavier loads. They often carry load range designations like C, D, E, or F, which correspond to the number of plies and the maximum load at a given inflation pressure. These ratings are defined in FMVSS 119, which includes strength and endurance tests that vary by size and load range.

P-metric tires use a load index number instead, a numeric code that represents a specific load capacity at a given pressure. The load rating is defined in 49 CFR 571.139 as the maximum load a tire is rated to carry for a given inflation pressure. For a given size, an LT tire generally has a higher load rating than a comparable P-metric tire.

One critical rule comes from 49 CFR 571.120: when a passenger car tire is installed on a multipurpose passenger vehicle, truck, bus, or trailer, its load rating must be reduced by dividing by 1.10 before calculating the sum of the load ratings on an axle. This derating means a P-metric tire used on a truck must be derated to account for the different dynamics and load distribution of heavier vehicles. For more on how load range and load index work together, see tire load index rating.

• LT tires are tested under FMVSS 119, which includes endurance and strength tests.
• P-metric tires are tested under FMVSS 139, which has its own set of requirements.
• When a P-metric tire is used on a truck, the load rating is reduced by a factor of 1.10 per FMVSS 120.

Inflation Pressure Differences

Inflation pressure is the other major differentiator. LT tires often require higher cold inflation pressures than P-metric tires to support their higher load capacities. The recommended pressure is always set by the vehicle manufacturer, not by the tire's sidewall maximum.

According to the U.S. Department of Energy's fueleconomy.gov, you should rely on the sticker inside the driver's door jamb or the owner's manual for the correct tire pressure, not the maximum pressure printed on the tire sidewall. Under-inflated tires can lower gas mileage by about 0.2% for every 1 psi drop in the average pressure of all tires, as noted on the same page.

LT tires have higher maximum inflation pressures than P-metric tires, but you should never exceed the vehicle's recommended pressure unless you are specifically adjusting for load. If you install LT tires on a vehicle that called for P-metric, the recommended pressure from the placard may not be sufficient for the LT tire's load rating. Conversely, overinflating a P-metric tire on a truck can lead to a harsh ride and uneven wear. Check tire pressure basics for a deeper look.

Intended Use and Vehicle Fitment

The core reason to choose one over the other is how you use the vehicle. P-metric tires are designed for cars, crossovers, and light-duty trucks that stay mostly on pavement and carry modest loads. They offer a smoother ride, lower rolling resistance, and better fuel economy, as explained in tire width and fuel economy.

LT tires are for trucks, vans, and SUVs that are used for towing, hauling, or off-road driving where extra capacity and sidewall stiffness are needed. Their heavier construction and higher load ratings make them essential when you regularly approach the vehicle's GVWR. The trade-off is a firmer ride and often slightly worse fuel economy on the highway.

The regulations in FMVSS 110 and 120 require that the sum of the maximum load ratings of the tires on an axle be at least equal to the axle's gross axle weight rating (GAWR). If you install P-metric tires on a heavy truck, the derating factor may make it impossible to meet that requirement, which is why many trucks come from the factory with LT tires. For additional guidance, see tire load index for towing safety and tire pressure for heavy SUVs.

What to Pick for Your Truck or SUV

The decision comes down to your typical load and driving conditions. If you drive a half-ton pickup or full-size SUV mainly as a daily commuter and only load the bed or hitch occasionally, a P-metric all-season or touring tire may be the better choice. It will give a quieter ride and better fuel economy, and the short-haul loads will not push the tire past its derated limit.

If you frequently tow a trailer, haul construction materials, or carry a heavy camper shell, switch to LT tires. Load range E (10-ply rated) and F are common choices for heavy use and are designed to maintain their shape at higher pressures. For light-duty use, load range C can work, but you need to confirm that the combined load rating meets your axle GAWR.

For off-road enthusiasts, LT all-terrain or mud-terrain tires provide the robust sidewalls needed for rock, sand, and trail work. See our best light truck tires and best all-terrain tires for size-specific recommendations, and read tire load range for pickup vs suv to match the rating to your vehicle.

What to pick for your vehicle use

Questions

Can I put LT tires on a passenger car?

You can, but it is not recommended. LT tires are heavier and stiffer, which will degrade ride comfort and fuel economy. The load capacity and pressure requirements are overkill for a car, and the handling will feel harsh. Unless you have a specific need for a heavy-duty tire, stick with P-metric tires for a car.

What does load range C, D, E, or F mean on an LT tire?

These letters correspond to the number of plies the tire is rated for under FMVSS 119. Load range C is typically 6-ply rated, D is 8-ply rated, E is 10-ply rated, and F is 12-ply rated. Higher letters mean higher load capacity at a given inflation pressure, allowing the tire to carry heavier loads.

Should I inflate LT tires to the pressure on the sidewall?

No. The sidewall shows the maximum permissible inflation pressure, not the recommended pressure. Always use the vehicle manufacturer's placard pressure or the adjusted pressure based on the actual load. Overinflating beyond the placard can reduce traction and cause premature center wear.

What happens if I overload a P-metric tire?

Overloading a P-metric tire can cause excessive heat buildup, leading to tread separation or a blowout. The derating rule in FMVSS 120 reduces the load capacity when used on a truck, so even if the tire appears to be rated high enough, the effective capacity is lower. It is safer to choose an LT tire for heavy loads.