• The two main factors limiting vehicle weight are the “rated” gross value and the “allowed” gross value.
• Maximum gross weight allowed is seldom achieved because of the direct influence of other considerations.

The Federal Highway Administration (FHWA) sets weights that states must allow on interstate highways, including the maximum gross vehicle weight at 80,000 pounds (subject to the Federal Bridge Law), the maximum gross weight upon any one axle at 20,000 pounds, and the maximum gross weight on tandem axles at 34,000 pounds.

The FHWA also covers the relationship of tire width and axle ratings: “States may not limit tire loads to less than 500 pounds per inch of tire or tread width, except that such limits may not be applied to tires on the steering axle. States may not limit steering axle weights to less than 20,000 pounds or the axle rating established by the manufacturer, whichever is lower.” Adding additional uncertainty with the “mays” and “may nots” are grandfathering dates and other exclusions.

There are two primary limiters of weight: the first is the “rated” gross value, and the second is the “allowed” gross value. These two are not just applied to the vehicle(s); they are also applied to axle groups, axles, and tires.

Usually, the maximum gross weight allowed will be the state’s maximum allowed gross. Carriers must be careful, though, because unless a load is perfectly balanced across the axles and groups, the maximum is rarely met due to one of the other limits, or strikes, being reached first. These limits include:

• The allowed axle weight(s) based on the state or local statutes,
• The allowed axle group weight based on the bridge law (each combination of axles and distance is determined separately),
• The allowed weight per tire or inch of tire width,
• Each tire’s rating, and
• The registered vehicle weight.