The tri-axle dump truck is a common workhorse in construction and material transport, employed for moving bulk materials like gravel, sand, and debris. Capacity is measured in cubic yards, a volumetric measurement indicating the physical space available within the truck’s bed. However, the actual amount of material a truck can legally carry is not a single, fixed number. Capacity changes based on the specific body dimensions and the physical properties of the material being transported.
Understanding the Tri-Axle Dump Truck
The designation “tri-axle” refers to the truck’s configuration, which includes a steering axle at the front and three axles clustered toward the rear of the vehicle. This setup typically consists of a tandem drive axle pair and a third axle, often a liftable “tag” or “pusher” axle. The primary function of this configuration is to distribute the total load across a greater number of tires and axle points.
This increased distribution directly relates to a higher allowed Gross Vehicle Weight Rating (GVWR) under federal and state regulations. By spreading the weight, the tri-axle setup significantly increases the maximum permitted payload compared to a standard tandem axle dump truck. This engineering choice allows the tri-axle model to be the preferred choice for maximizing material transport efficiency on public roadways.
Standard Capacity in Cubic Yards
When considering only the physical volume of the container, a standard tri-axle dump truck is typically designed to hold between 15 and 20 cubic yards of material. This range reflects the internal dimensions of the truck body, specifically its length, width, and side height. The capacity is calculated by multiplying these three dimensions to determine the total physical space available for carrying a level load.
For instance, a truck bed measuring 16 feet long, 8 feet wide, and 4 feet high holds approximately 18.9 cubic yards of material when filled level to the top. This volumetric measurement is most relevant when hauling materials that are relatively light and bulky. These materials include dry, shredded wood mulch, snow, light topsoil, or certain types of construction debris.
These lighter materials rarely utilize the truck’s maximum legal weight capacity, making the physical size of the truck body the limiting factor for how much can be transported in a single trip. For example, a cubic yard of dry, shredded mulch might weigh less than 500 pounds, meaning a 20-yard load would weigh only about five tons.
Volume vs. Weight: The Payload Constraint
While a tri-axle dump truck may physically contain 20 cubic yards of volume, the actual amount of material hauled is almost always constrained by weight, not space, when dealing with dense materials. Material density, measured in pounds per cubic yard, is the determining factor that translates the volumetric capacity into a legal payload. The truck’s maximum legal payload is dictated by its Gross Vehicle Weight Rating (GVWR) and, more specifically, the maximum weight allowed on each individual axle.
For example, a cubic yard of dry sand or gravel typically weighs around 2,800 to 3,000 pounds, which is substantially heavier than light topsoil or mulch. If a tri-axle truck has a maximum payload capacity of 20 to 22 tons, which is 40,000 to 44,000 pounds, it cannot utilize its full 20-yard volume when hauling heavy stone. A 20-ton limit would only allow for approximately 13 to 14 cubic yards of this heavy material before the legal weight is reached.
Exceeding these weight limits, even if the material fits within the bed walls, results in violations of Department of Transportation (DOT) regulations. These regulations are designed to protect public infrastructure, such as bridges and roadways, from excessive stress. A material like crushed concrete, which is exceptionally dense, will significantly reduce the effective yardage a tri-axle truck can carry. Haulers must calculate the material’s specific density to determine the safe and legal volume, often resulting in loads that are visually below the top of the truck body.