Load Ranges and Ply Ratings are important indicators of tire strength and behavior under load. Ply Ratings are especially important if you tow, go off road, carry heavy loads or drive at competitive speeds, such as on a road course at a private club. On truck tires, Ply Ratings are also known as Load Ranges.
Most passenger tires are Standard Load, which can be inflated to 35 psi. Standard Load is designated by the letters SL — or, more typically, by no letters at all. So, a passenger tire that’s sized 235-60R15 is Standard Load — the same as if it were labeled 235-60R15SL.
Extra Load passenger tires are designated XL. They are found most often in high-performance lines. XL tires, which can be inflated up to 42 psi, are better at handling heat and cornering forces.
Light Load passenger tires are rare and are designated LL.
Load Ranges and their corresponding Ply Ratings have become more important as more drivers buy trucks, including pickups, SUVs and full-size vans. A higher Load Range may benefit you if your truck is doing real work, such as towing a boat, camper or trailer; carrying heavy loads; making job site deliveries, or traveling far off road where conditions can harm lower-strength.
Tires with higher Load Ranges can be inflated to higher pressures. They also flex less, so they are more stable under load.
The higher the Load Range — an E Load Range is higher than a D, which is higher than a C, and so on — the higher the Ply Rating.
Ply Ratings used to refer to the actual number of plies — rubber layers with fabric cords — that made up the casing of the tire and were cured under pressure and heat during manufacturing. More plies made a tire stronger. Today, few tires have more than 3 plies, with heavy truck tires occasionally having 4. Instead the tires have a Ply Rating, which indicates stiffness equivalent to a higher number of plies. Passenger tires almost always have a Ply Rating of 4.
For light truck tires, each Load Range has a corresponding Ply Rating and maximum inflation pressure:
|Load Range||Ply Rating||Maximum PSI|
Load Range B is the same as Standard Load. As letters and numbers climb, you’re getting a stronger, stiffer tire. Stiffer tires are less likely to squirm under load. And for serious off-roading, you’re putting a stronger tire against the greater hazards of unpaved surfaces, including rocks and ruts.
There’s a tradeoff for the stronger, less pliant sidewalls of high Load Ranges: They are likely to generate a stiffer ride. That may not matter if your truck or van is a true work vehicle. But it may matter on an everyday driver, such as an SUV. You may experience a somewhat less comfortable everyday ride by adding stronger tires to tow a recreational vehicle or go off-road only a couple of times a year.
Higher Load Range, besides changing ride characteristics, can affect handling. It’s best to match Load Range when buying tires if you’re replacing just one or two tires.
And don’t confuse Load Range letters with Speed Rating codes. Speed ratings (T, S, V, W, Y and Z are seen most often) have nothing to do with load-carrying capability.