Tractor Trailer Axle Weights
Tractor Trailer Axle Weights
William Thomas / January 2021
The Formula Governing Tractor Trailer Axle Weights in Towing Industry
The Federal Highway Administration devised a formula (the bridge formula) that defines the maximum load weight that a trailer with a given set of axles can carry when trucking through interstate highways and major road routes in North America. Ideally, the formula was enacted to limit the weight to length ratio of a loaded trailer and truck towing a load across a bridge. According to the length, the weight-to-length ratio can be achieved by increasing the distance between consecutive axles or the trailer having additional axles. The purpose of the weight-to-length ratio is primarily to protect the bridges since the closely spaced the axles are, the more stress a loaded trailer exerts on roads and bridges.
The overall gross weight on a set of two pairs or more consecutive axles, the number of axles, and the length (in ft.) between a set of two axles and the outer axle are the three principal variables used in the formula. With the bridge formula, you can use the dimensions, and gross weight of your trailer, to determine the weight limit compliance of a single or multiple axle trailer. The weight limit of a trucking vehicle does not stop with the bridge formula. The U.S Department of Transportation, through the Federal Highway Administration further establishes that; for a single axle trailer, its load limit is 20,000 lb, and trailers with tandem axles spaced between 40 to 90 in. has a load limit of 34,000 lb. The department further states that the gross weight limit for multiple axle trailer is 80, 000 lb. It’s important to note that the weight limit defined by the bridge formula holds as long a state law does not dictate a lower weight limit.
Understanding Tractor Trailer Axle Weights in Heavy Equipment Delivery
Understanding axle weights in the heavy machinery moving industry is the key to seamless trucking services. With a better understanding of the tractor-trailer axle weights, a towing company will always operate within the law as well as minimizing tear and wear caused by “poor” distribution of weight.
A standard trailer has steer axle, drive tandem, and trailer tandem axles. Other tractor trailer axle configurations include tri-axle, quad-axle, and single-axle. Each trailer axle configurations are heavily governed by the axle weight, axle spacing, gross weight, tire width, and the ratings as specified by manufacturers.
States Tractor Trailer Axle Weights Limits Regulations in Heavy Trucking
As mentioned above, all trucks towing heavy equipment on the interstate roadways must adhere to the federal bridge formula. Even though the federal government does not have the mandate to issue permits, any load that exceeds weight limits under the bridge formula must be issued with overweight permits. Since the federal government has allowed the states and provinces to enact their own set of regulations and restrictions, you need to find out the axle weight limits for each state so that you can plan well on distributing your load weight while trucking through each state’s highways. For instance, for a single axle trailer, a weight limit of 25,000 lbs. is permitted when crossing Texas highways. Luckily, our logistic team at Heavy Equipment Transport knows each state and province laws and are ready to help you move your heavy equipment anywhere across North America, Mexico, and Canada.
Factors Affecting Tractor Trailer Axle Weights When Trucking Heavy Loads
Although the gross weight does not depend on the weight transfer, the following factors will affect weight distribution across the axles of the trailer.
- Repositioning your trailer’s tandem axles.
- Sliding your trailer’s 5th wheel, either backward or forward
- Positions of the fuel tanks and the amount of fuel stored in the tanks
- The front-to-back lateral position of the load in the trailer
- The position of the center of gravity of the load in relation to the gross weight.