Pup trailer

Why it matters

A pup adds axles and length, and under the federal Bridge Formula more axles spread farther apart mean more legal weight. That's the whole point of a dump truck with a pup trailer: a tandem that's capped at about 51,000 lb on the Interstate can run a combination up to the 80,000 lb federal limit with enough spacing.

Tandem dump, 20 ft first to last axle

51,000 lb gross

Truck + 2-axle pup, 51 ft

80,000 lb gross

EXAMPLE empty weight, truck and pup

40,000 lb

Legal payload with the pup

20 tons

License

Class A CDL

Bridge Formula, 23 CFR 658.17, Interstate. States set other roads. Weigh your own rig.

The trade-offs: a Class A CDL for every driver (a towed unit over 10,000 lb in a combination over 26,000 lb), a second body and hoist to maintain, and more time backing and dumping at tight sites.

The 28 foot pup trailer

In freight hauling, pups run in pairs as doubles, common in less-than-truckload work. Federal rules protect their length on the National Network: under 23 CFR 658.13(b)(2), no state may limit a semitrailer or trailer in a tractor-semitrailer-trailer combination to less than 28 feet, and 28.5-foot trailers in lawful use on December 1, 1982 are grandfathered under (b)(5).

Source: 23 CFR 658.13, Length (eCFR) · checked 2026-10

Pup trailer hauling in practice

• Dump pups dump on their own, so the driver dumps the truck, then backs or pulls to dump the pup. A transfer trailer works differently: its box rolls into the truck body. Both are covered in super 10 dump trucks.
• Check the spacing before you buy: a pup that's too short won't reach the gross you're paying for. Run it in the Bridge Formula calculator.
• Lift axles on the truck still count only when they're down; see lift axle.

Related: CDL classes, LTL freight, types of dump trucks.

TruckSprint no longer dispatches dump trucks. For road freight, our desk dispatches equipment like the 26 ft box truck.