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The Importance of Axle Ratings and Gross Vehicle Weight
When transporting heavy machinery like excavators or loaders, understanding the relationship between axle ratings and gross vehicle weight rating (GVWR) is essential. Axle ratings refer to the maximum weight each axle can safely support, as determined by the manufacturer. For example, a Kenworth W900 semi tractor may have a front axle rated at 13,200 pounds and rear tandems rated at 46,000 pounds, totaling 59,200 pounds.
However, this figure does not represent the total weight the truck can legally haul. GVWR includes the combined weight of the truck, trailer, and payload. It’s influenced not only by axle ratings but also by suspension design, tire capacity, and—most importantly—state and federal bridge laws.
Bridge Law and Legal Load Distribution
Bridge law governs how weight is distributed across axles based on spacing. In most U.S. states, the legal gross weight without special permits is 80,000 pounds. This includes:
Permits and Specialized Equipment
To move such loads legally, operators must obtain oversize/overweight permits. These vary by state and may require:
Lift Axles and Load Management
Some dump trucks and tractors use lift axles to increase legal carrying capacity. These are auxiliary axles that can be lowered to distribute weight when on pavement and lifted when off-road. A dump truck with 20,000-pound front axle, 46,000-pound rear tandems, and two 8,000-pound lift axles might have a manufacturer-rated capacity of 82,000 pounds. However, bridge law may only allow 60,500 pounds depending on wheelbase and axle spacing.
Real-World Example and Practical Considerations
A contractor operating in Oregon used a Kenworth T800 with a Truckweld dump trailer and three 22,500-pound axles. With proper spacing, the legal bridge load was 105,500 pounds, allowing the transport of 33 tons of gravel. In contrast, a Peterbilt tractor with a Trail King TK70 lowboy and no lift axle was limited to 80,000 pounds, barely enough to haul a 43,000-pound John Deere 690D excavator.
Conclusion
Axle ratings provide a mechanical ceiling, but legal hauling limits are governed by bridge law and state regulations. Operators must consider not just the truck and trailer specs, but also route restrictions, permit requirements, and load distribution strategies. Understanding these factors ensures safe, legal, and efficient transport of heavy equipment—whether moving a compact backhoe or a full-size excavator.
When transporting heavy machinery like excavators or loaders, understanding the relationship between axle ratings and gross vehicle weight rating (GVWR) is essential. Axle ratings refer to the maximum weight each axle can safely support, as determined by the manufacturer. For example, a Kenworth W900 semi tractor may have a front axle rated at 13,200 pounds and rear tandems rated at 46,000 pounds, totaling 59,200 pounds.
However, this figure does not represent the total weight the truck can legally haul. GVWR includes the combined weight of the truck, trailer, and payload. It’s influenced not only by axle ratings but also by suspension design, tire capacity, and—most importantly—state and federal bridge laws.
Bridge Law and Legal Load Distribution
Bridge law governs how weight is distributed across axles based on spacing. In most U.S. states, the legal gross weight without special permits is 80,000 pounds. This includes:
- Tractor weight
- Trailer weight
- Payload (e.g., excavator or loader)
Permits and Specialized Equipment
To move such loads legally, operators must obtain oversize/overweight permits. These vary by state and may require:
- Route planning to avoid restricted bridges
- Escort vehicles
- Travel time restrictions (e.g., daylight hours only)
Lift Axles and Load Management
Some dump trucks and tractors use lift axles to increase legal carrying capacity. These are auxiliary axles that can be lowered to distribute weight when on pavement and lifted when off-road. A dump truck with 20,000-pound front axle, 46,000-pound rear tandems, and two 8,000-pound lift axles might have a manufacturer-rated capacity of 82,000 pounds. However, bridge law may only allow 60,500 pounds depending on wheelbase and axle spacing.
Real-World Example and Practical Considerations
A contractor operating in Oregon used a Kenworth T800 with a Truckweld dump trailer and three 22,500-pound axles. With proper spacing, the legal bridge load was 105,500 pounds, allowing the transport of 33 tons of gravel. In contrast, a Peterbilt tractor with a Trail King TK70 lowboy and no lift axle was limited to 80,000 pounds, barely enough to haul a 43,000-pound John Deere 690D excavator.
Conclusion
Axle ratings provide a mechanical ceiling, but legal hauling limits are governed by bridge law and state regulations. Operators must consider not just the truck and trailer specs, but also route restrictions, permit requirements, and load distribution strategies. Understanding these factors ensures safe, legal, and efficient transport of heavy equipment—whether moving a compact backhoe or a full-size excavator.
