LT vs Passenger Tire Speed Ratings: What Differs

Passenger car tires and LT tires are defined by the federal rules

Federal standards draw the first boundary by vehicle weight. A passenger car tire is a tire intended for use on passenger cars, multipurpose passenger vehicles, and trucks with a gross vehicle weight rating (GVWR) of 10,000 pounds or less. An LT tire, by contrast, is a tire designated by its manufacturer as primarily intended for use on lightweight trucks or multipurpose passenger vehicles.

That wording matters more than the letter on the sidewall. It determines which federal standard applies, how the tire is tested, and how its load rating is calculated. New pneumatic radial tires for light vehicles are covered by FMVSS 139. Bias ply tires and T-type spare tires are covered by FMVSS 109. LT tires with a tread depth of 18/32 inch or greater, even when mounted on a vehicle with a GVWR of 10,000 pounds or less, are also covered by FMVSS 119.

Load range and speed symbol answer different questions

Load range is a shorthand for a tire's load-carrying construction. The federal strength tests use the tire's size and load range to set the required breaking energy, which is why LT tires are often sold with load range labels such as C, D, or E. The speed rating, in turn, is the part of the service description that states the tire's maximum speed capability.

These are separate markings, but they interact. A tire that is not in the right load range for your axle ratings is overloaded no matter what speed symbol it carries, and a tire with a low speed symbol is not the right choice for sustained high-speed driving even if its load range is ample. For the practical meanings of the speed symbols, see our tire speed rating guide. For the construction differences between tire classes, read what is tire load range.

Federal load rules explain why the tire class matters

FMVSS 110 limits how hard a passenger car tire can be loaded. For passenger cars, the vehicle normal load on a tire must not exceed 94 percent of the load rating at the vehicle manufacturer's recommended cold inflation pressure. The vehicle maximum load on the tire must not be greater than the maximum load rating marked on the sidewall. These margins exist because real-world loads shift, and a tire's load rating is tied to its inflation pressure.

The heavy-vehicle rule goes further. Under FMVSS 120, when a passenger car tire is installed on a multipurpose passenger vehicle, truck, bus, or trailer, the tire's load rating is divided by 1.10 before the axle load is calculated. That single derating is the easiest way to see the speed-and-load relationship: the passenger tire class is not treated the same as the LT class once it moves to truck duty.

The 10,000-pound GVWR boundary changes the test standard

FMVSS 119 is the tire standard for vehicles with a GVWR of more than 10,000 pounds, as well as for specialty tires and motorcycle tires. FMVSS 120 adds tire and rim selection rules for those vehicles. If you are shopping for a heavy pickup, a commercial van, or a trailer, the tire class has to line up with those standards, not just with the speed symbol.

The selection rule is practical: the sum of the maximum load ratings of the tires fitted to an axle must not be less than the gross axle weight rating for that axle. When a passenger car tire is used on a truck, bus, or trailer in this class, the 1.10 derating applies. For most heavy trucks, an LT tire in the right load range, or a commercial tire where the vehicle is over the threshold, is the safer match.

The purpose language of FMVSS 120 ties it together: vehicles must be equipped with tires of adequate size and load rating and with rims of appropriate size and type designation. In other words, the legal decision is based on load first and speed second.

Choose the tire class before you compare speed ratings

Start with the vehicle placard. It lists the original tire sizes, recommended cold inflation pressures, and axle ratings. A car, crossover, or SUV that stays near its factory load can usually keep a passenger car tire. A pickup that carries cargo, tows, or works off-road is often better with an LT tire because the LT class is built around higher loads and inflation pressures.

After you confirm the tire class and load range, compare speed ratings. The speed symbol still matters for highway use, but it does not override the load calculation. For an everyday car or SUV, start with our best all-season tires for cars and SUVs. For a mixed-duty pickup, look at the best light truck tires and match the load range to your axle ratings.

Speed rating mistakes to avoid

The most common mistake is shopping by speed rating before load range. Another is assuming an LT version of the same size will behave exactly like the passenger version. LT tires can carry a range of speed symbols, so read the service description on the sidewall instead of guessing.

Before you buy, decode the service description and the sidewall markings. For typical car fitments, the tire speed rating guide explains the symbols; for heavy commercial fitments, the commercial tire guide is a better starting point.

• Do not choose a tire only by the speed symbol if the vehicle label calls for an LT tire or a higher load range.
• Do not assume a passenger tire on a light truck carries the same load it would carry on a passenger car; the 1.10 derating under FMVSS 120 applies in truck, bus, and trailer service above 10,000 pounds GVWR.
• Do not use a higher speed symbol to avoid the 94 percent normal-load rule for passenger car tires.
• Do not overlook deep-tread LT tires: a tire with 18/32 inch or more tread depth can fall under FMVSS 119 even on a vehicle rated 10,000 pounds or less.

What to pick for your use

Questions

Can I put passenger car tires on a light truck?

Yes in some cases. Federal rules define a passenger car tire as a tire intended for use on passenger cars, multipurpose passenger vehicles, and trucks with a GVWR of 10,000 pounds or less. For a light-duty truck, the passenger tire class is allowed if the load limits in FMVSS 110 are met. For heavier truck service above 10,000 pounds GVWR, FMVSS 120 applies the 1.10 derating rule.

Do LT tires have higher speed ratings than passenger tires?

Not automatically. The speed symbol is part of the service description, and LT tires are available with a range of speed symbols. The more important difference is construction and load range. Read the sidewall on the specific tire and compare it with the vehicle placard.

Does load range affect speed rating?

They are separate markings, but you need both. Load range describes construction and load-inflation capacity for heavy service. The speed symbol describes maximum speed capability. Choose the correct load range first, then confirm the speed symbol matches your highway use.

What is the 1.10 rule for passenger tires on trucks?

FMVSS 120 says that when a passenger car tire is installed on a multipurpose passenger vehicle, truck, bus, or trailer, the tire's load rating is reduced by dividing by 1.10 before calculating the sum of load ratings on an axle. This rule appears in the standard for vehicles with a GVWR above 10,000 pounds, and it is why truck fitments need a tire class that matches the axle ratings.

Can a higher speed rating replace the right load range?

No. A higher speed symbol does not increase the tire's load rating. If the tire is not in the correct load range for the axle, the tire can be overloaded even if the speed symbol looks fast. Match the load range and load index first, then compare speed ratings.