A heavy-truck tire sidewall carries nearly everything you need to spec a replacement correctly, printed in a code that fits in a few inches of molded rubber. For a Québec fleet manager comparing options, learning to read that code is faster than calling a supplier for every unit and more reliable than guessing from the old tire’s worn tread. The markings tell you dimensions, construction, load capacity, speed tolerance, and how the tire is meant to be used.
What the Numbers Mean
Start with the main size string, which on a steer or drive tire often looks like 11R22.5 or 295/75R22.5. The first number is the section width, either in inches (11) or millimetres (295). When a two-number format appears, the second figure is the aspect ratio: 75 means the sidewall height is 75 percent of the width. A lower ratio gives a shorter, stiffer sidewall.
The letter R stands for radial construction, which is standard on virtually all modern highway trucks. The last number, 22.5, is the rim diameter in inches. Match that number exactly to your wheels, because a 22.5 tire will not seat on a 24.5 rim no matter how close the other figures look.
Elsewhere on the sidewall you will find the tread depth in 32nds, the DOT code with the week and year of manufacture, and the ply or load range letter. The DOT date matters in Québec’s climate, where tires that sit in a yard through long winters age even without rolling.
Load and Speed Ratings
After the size comes the load index and speed symbol, printed as something like 146/143L. Those two numbers cover single and dual applications: the higher figure applies when the tire runs alone, the lower when it is mounted as part of a dual set, where each tire carries slightly less. Convert the index through a standard load chart to get the actual weight in kilograms per tire, then multiply across the axle to confirm the assembly can legally carry your loaded configuration.
The letter after the load index is the speed symbol. On heavy highway tires you will commonly see L, which corresponds to 120 km/h, well above the posted limits on Autoroute 20 or the 40, but the margin accounts for sustained high-speed running in summer heat. Do not treat the speed symbol as a target; it is a ceiling tied to the tire’s construction and inflation.
Inflation pressure is where many of these ratings come to life, because the stamped load capacity assumes the tire is inflated to its rated cold pressure. Underinflated tires on a fully loaded trailer lose capacity quickly, run hot, and wear unevenly. Suppliers such as long-haul road treads can help cross-check the index against your typical axle weights so you are not reading the chart in isolation. Getting the pairing of load and pressure right is the single most important safety step in spec work.
Matching long-haul road treads
Beyond the raw numbers, the sidewall and tread pattern tell you the intended service. Highway steer and drive tires carry different tread designs than regional or on/off-road units, and some are marked with symbols for severe snow service. In Québec, where winter regulations require winter-rated tires on certain vehicles during the mandated period, that marking is not optional reading. Look for the three-peak mountain snowflake where it applies to your class of vehicle.
A long-haul fleet running mostly between Montréal, Québec City, and points south benefits from low-rolling-resistance rib patterns on the steer and closed-shoulder drive tires that favour even wear over aggressive traction. A fleet doing regional pickup and delivery with frequent stops will scrub tread differently and may need a more durable casing. Reading the full sidewall lets you match the tire to the duty cycle rather than defaulting to whatever was on the truck before.
Next step: pull one tire from each axle position on a representative truck, photograph the complete sidewall, and build a short spec sheet from those codes so every future reorder starts from verified numbers instead of memory.