What Is Tandem Axle in Trucking?
Also called: Tandem Axle Weight, Dual Axle, Drive Tandem, 34,000 Pound Axle Limit
A tandem axle is a group of two or more axles whose centers are more than 40 inches and not more than 96 inches apart. On the Interstate, federal law caps the weight on a tandem axle at 34,000 pounds. A single axle may carry 20,000 pounds and the whole vehicle 80,000 pounds. Axles farther apart are checked with the bridge formula.
Last reviewed September 23, 2026 · Facts checked October 21, 2026
Key Points
- Tandem axle weight is the total weight on two or more consecutive axles whose centers are more than 40 inches and not more than 96 inches apart (23 CFR 658.5)
- The federal tandem axle limit on the Interstate is 34,000 pounds (23 CFR 658.17(d))
- A single axle weight counts axles not more than 40 inches apart, with a limit of 20,000 pounds (23 CFR 658.5 and 658.17(c))
- Gross vehicle weight is limited to 80,000 pounds, unless the bridge formula allows less (23 CFR 658.17(b))
- A State may not enforce a tandem limit under 34,000 pounds on the Interstate, including enforcement tolerances (658.17(f))
- Axles more than 96 inches apart are checked with the bridge formula. At 97 inches apart, FHWA says two axles may carry 38,000 pounds and three axles 42,000 pounds
- A common five-axle tractor-trailer is a steer axle plus two tandems. FHWA's example is 12,000 pounds on the steer axle and 17,000 pounds on each of the other four axles, for 80,000 pounds
What is a tandem axle on a truck?
A tandem axle is a pair, or a group, of axles that sit close together and share the load. The federal definition is two or more consecutive axles whose centers are more than 40 inches and not more than 96 inches apart. On a tractor-trailer, the two drive axles are one tandem, and the two trailer axles are another.
What is the weight limit on a tandem axle?
On the Interstate, the federal limit is 34,000 pounds on a tandem axle (23 CFR 658.17(d)). A single axle may carry 20,000 pounds, and the whole vehicle 80,000 pounds. The weights include all tolerances, except a scale allowance for portable scales that may not be more than 5 percent (658.17(g)). A State may not enforce a lower tandem limit on the Interstate (658.17(f)).
How is a tandem axle different from a single axle?
It comes down to spacing. Axles whose centers are not more than 40 inches apart count as one single axle weight. Axles more than 40 and not more than 96 inches apart count as a tandem. Farther apart, the bridge formula sets the limit. At 97 inches apart, FHWA says two axles may carry 38,000 pounds, which is more than the tandem limit.
Can a tandem axle carry more than 34,000 pounds?
In some cases. States may issue special permits for loads that cannot be divided, without regard to the federal axle limits (23 CFR 658.17(h)). Higher limits that were legal under State law on certain older dates are grandfathered (658.17(i)). A vehicle with an auxiliary power unit that cuts idling may carry up to 400 more pounds in a tandem weight if the unit's weight is certified and it works (658.17(n)). Check your State's rules and permits before you rely on any of these.
Why does tandem spacing matter?
Spacing changes how weight is shared. Two consecutive sets of tandems may each carry 34,000 pounds if the distance from the first axle to the last is 36 feet or more (23 CFR 658.17(e)). If the spacing is shorter, the bridge formula may allow less. Weigh each axle group, not only the whole truck.
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Frequently Asked Questions
What is a tandem axle?+
Two or more consecutive axles whose centers are more than 40 inches and not more than 96 inches apart (23 CFR 658.5). Most drive tandems and trailer tandems fit this.
What is the legal weight for tandem axles?+
34,000 pounds on the Interstate (23 CFR 658.17(d)). The limit includes all enforcement tolerances, except a scale allowance for portable scales.
How many axles does a tandem have?+
The federal definition says two or more consecutive axles in the 40 to 96 inch range. A tandem on a tractor or trailer is usually two axles.
What is the difference between a single axle and a tandem?+
A single axle weight counts axles not more than 40 inches apart, with a 20,000 pound limit. A tandem counts axles more than 40 and not more than 96 inches apart, with a 34,000 pound limit.
Can a State set a lower tandem axle limit?+
Not on the Interstate. A State may not enforce a tandem limit under 34,000 pounds there (23 CFR 658.17(f)). Other roads follow State law.
Do I need a permit to carry more than 34,000 pounds on a tandem?+
A State permit is how loads that cannot be divided may go over the federal axle limits (23 CFR 658.17(h)). Ask the State you will drive in, because permits are issued by States.
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This is industry terminology and typical practice. It is not legal or tax advice. Rates, fees, and rules mentioned are general ranges. Confirm the details on your rate confirmation, carrier agreement, or a current official source.