On the Interstate, the federal axle weight limits are 20,000 pounds on a single axle, 34,000 pounds on a tandem axle group, and 80,000 pounds gross, with the bridge formula capping weight on every group of axles in between. The steer axle is handled differently: federal rules do not set one fixed steer figure, they set a floor on what a state may enforce. Off the Interstate, each state sets its own limits, and they can be lower.

This guide covers the federal limits, how to read them against a scale ticket, and how three states differ. For the formula that sits underneath them, see the federal bridge formula, explained.

The federal limits at a glance

These come from 23 CFR 658.17 and apply to the National System of Interstate and Defense Highways and reasonable access to it.

  • Single axle: 20,000 pounds on any one axle, including any one axle of a group.
  • Tandem axle: 34,000 pounds on a tandem group.
  • Gross vehicle weight: 80,000 pounds, or less where the bridge formula gives a lower figure for the truck's axle spacing.
  • Steer axle: no fixed figure, but a floor on state limits. See below.

All four have to pass at once. The lowest answer wins.

What counts as a single axle or a tandem

The definitions are in 23 CFR 658.5, and they are about axle centers, not about what the axles are called.

  • A single axle weight is the total weight carried by all wheels whose centers fall between two parallel vertical planes 40 inches apart.
  • A tandem axle weight is the total weight carried by two or more consecutive axles whose centers can be included between parallel vertical planes spaced more than 40 inches and not more than 96 inches apart.

So two axles 52 inches apart are one tandem group with a 34,000 pound limit, not two single axles with 20,000 pounds each.

The steer axle is a floor for states, not a cap

The federal rule does not say a steer axle may carry 12,000 pounds, or 20,000 pounds. It says what a state may not do. Under 23 CFR 658.17(f), a state may not limit steering axle weights on the Interstate to less than 20,000 pounds or the axle rating set by the manufacturer, whichever is lower.

In practice, a state must allow a steer axle at least the manufacturer's axle rating or 20,000 pounds, whichever is lower. North Dakota and Wisconsin, for example, tie it to the manufacturer's rating with a 20,000 pound cap. Check the rating on the axle before you load.

Tires work the same way. A state may not limit tire loads to less than 500 pounds per inch of tire or tread width, and that limit may not be applied to tires on the steering axle.

How to read a scale ticket

A scale ticket splits the truck into axle groups. Check each one:

  1. Steer axle: under the manufacturer's rating, and under the state limit where it applies.
  2. Drive group: under 34,000 pounds if it is a tandem, and no single axle over 20,000 pounds.
  3. Trailer group: the same test for the trailer tandem.
  4. Gross weight: under 80,000 pounds.
  5. Bridge formula: every group of two or more consecutive axles, including inner groups, not only steer to last axle.

The limits include all tolerances. The only enforcement allowance is for portable scales, and it cannot exceed 5 percent. Separately, 23 CFR 658.17(n) allows up to 400 extra pounds for a vehicle with a certified idle-reduction unit. Fine schedules that charge nothing up to a threshold are treated as tolerances, which federal law does not authorize.

Use the bridge formula calculator for steps 4 and 5.

When one axle is over

Moving weight between axle groups changes the split but not the gross. Moving the load or the fifth wheel shifts weight between the steer, drive and trailer groups, and one axle can come into limits while another goes out. Weigh again after any change.

If the gross itself is over, the only fix is to take weight off. A load that cannot be divided may qualify for a permit instead: 23 CFR 658.17(h) lets states issue special permits without regard to the axle, gross or bridge formula requirements for nondivisible vehicles or loads. Start at the oversize and overweight permit pages, and see how to read a state oversize permit for what the conditions mean.

State limits and how the wording differs

The federal limits set a floor on the Interstate. States also set their own limits, and the wording differs. Three examples from the states' own sources:

  • North Dakota: the Highway Patrol's weight limitations chart says the weight on the steering axle is determined by the manufacturer's axle rating and may not exceed 20,000 pounds on the Interstate or on Defense Highways (Defense Highway travel is for Department of Defense loads).
  • Wisconsin: on class A highways, the steering axle of a truck tractor may not exceed 13,000 pounds unless the manufacturer's rated capacity of the axle and the tires is sufficient, and never more than 20,000 pounds (Wis. Stat. 348.15(3)(b)).
  • Michigan: axle loads depend on axle spacing. For axles 9 feet or more apart on high pressure pneumatic or balloon tires the maximum is 18,000 pounds, and wheel load may not exceed 700 pounds per inch of tire width (MCL 257.722). Michigan also reduces allowable axle loads in spring, with exceptions, so check the current season.

These are examples, not a full list. Check the state's own rules for the road you plan to use.

Grandfathered limits

The federal limits do not override every older state limit. Under 23 CFR 658.17(i), the single axle, tandem axle and gross limits do not apply to weights that state law legally authorized on July 1, 1956. A state can keep an older, higher limit that it had at that date.

Check your own numbers

Run the axle count and spacing through the bridge formula calculator, then compare the result with the state's own limits on the permit pages.

Related guides

Sources