Loading and axle weight glossary
Updated October 18, 2026
The terms you meet when planning a load, explained simply. French equivalents, used in Quebec and on some scale tickets, are given in brackets.
Coupling
- Kingpin (pivot d’attelage)
- The pin under the trailer nose that locks into the tractor’s fifth wheel. Part of the trailer’s weight goes through this point.
- Fifth wheel (sellette d’attelage)
- The tractor plate that receives the kingpin. On many tractors it slides: moving it forward puts more weight on the steer axle.
- Slider or sliding tandem (chariot coulissant)
- The frame carrying the trailer axles, which moves along rails, usually in 6-inch holes. Its position splits the weight between the trailer and the tractor.
- Wheelbase (empattement)
- The distance from the tractor’s front axle to the center of its drive tandem.
Axles
- Steer axle (essieu directeur)
- The tractor’s front axle, which steers the vehicle.
- Drive axles (essieux moteurs)
- The tractor axle group that delivers power, usually a tandem.
- Tandem
- A group of two closely spaced axles joined by a suspension that equalizes the load between them.
- Tridem
- A group of three evenly spaced axles. Its load limit depends on the spread, the distance from the first to the last axle.
- Dual tires and wide-base tires
- Two tires mounted side by side at each end of the axle, or one wide tire (445 mm or more) that replaces them.
Weights
- Tare
- A vehicle’s empty weight, with its equipment and fuel.
- Payload (charge utile)
- The weight of the freight carried.
- Gross weight (masse totale en charge)
- The total weight of the loaded combination: tractor, trailer, fuel and freight.
- Axle load (charge axiale)
- The weight an axle or axle group puts on the road.
- GAWR (PNBE)
- Gross axle weight rating: the maximum axle load set by the manufacturer, shown on the vehicle’s plate.
Regulations
- Spring thaw, frost laws (période de dégel)
- The spring period when allowed loads drop because roads are weakened. See Quebec spring thaw.
- Bridge Formula
- The US federal formula that limits the weight on a group of axles according to their number and spacing. See Axle weight limits.
- KPRA (kingpin to rear axle)
- The distance from the kingpin to the center of the rear axles, limited to 40 feet in California. See The 40-foot rule.
- Certified scale
- A scale inspected and approved for trade, whose ticket is official.
More guides
AxleLoad 53 user guideHow to plan a load in AxleLoad 53: regulations, equipment, pallets, reading the gauges and saving loads.Axle weight limits in Canada and the United StatesSteer, tandem, tridem, gross weight and the Bridge Formula: the limits that apply to a tractor with a 53-foot semi-trailer.Balancing a 53-foot trailer: slider, fifth wheel and palletsHow pallet weight splits between the kingpin and the trailer axles, and how many pounds each slider hole or fifth-wheel notch moves.Quebec spring thaw: zones, dates and load reductionsWhy allowed loads drop every spring in Quebec, how the thaw zones work and how to plan your loads.California’s 40-foot kingpin-to-axle ruleWhat California’s 40-foot KPRA rule measures, how to check it on a 53-foot trailer and how it changes your axle weights.Weighing your truck on a certified scaleHow to weigh axle group by axle group, read a scale ticket and measure your tares for more accurate calculations.AxleLoad 53 frequently asked questionsAnswers about the calculation, accuracy, regulations, spring thaw, accounts, the subscription and privacy.About AxleLoad 53 and contactWho builds AxleLoad 53, where the load limits come from, and how to reach us.
This guide is for information only. Legal limits change and depend on the road, the season and your permits: always check with the competent authority. Certified scale weights govern.