A tractor unit can tow trailers thanks to a converter dolly.

Learn about the many components and styles available for converter dollies.

A Converter Dolly Is What?

An unpowered commercial vehicle called a converter dolly is used to attach to tractor units so they can haul trailers.

It consists of a fifth wheel (coupling mechanism), a drawbar, and a chassis with one or more axles.

When hauling a second or third trailer, converter dollies support the front end of the semi-trailer.

Because they link trailers like railroad carriages, trailer converter dollies are sometimes known as road train dollies.

(In the trucking business in Australia, the phrase “road trains” is more often used.) A “doubles” combination is when a tractor pulls two trailers, while a “triples” combination is when it pulls three trailers.

A Converter Dolly’s Components

A converter dolly’s essential parts are as follows:

  • Axles: There are one to three axles on converter dollies. One axle and one pair of wheels are included in single axle dollies. Two sets of axles, one directly behind the other, make up a tandem axle dolly.
  • Fifth-wheel coupler: A semi-trailer kingpin and the dolly are connected by a sliding fifth wheel coupler.
  • Drawbar: Dollies may be equipped with a single or double tow drawbar for connecting to the trailer being towed. (See below for kinds of dollies.) Both types of towbars have a towing eye at the end.
  • Pintle hitch: The drawbar eye is engaged and supported by a hook on the hitch, which also has a locking mechanism to keep the eye in place.
  • Brakes: Antilock brakes are required on converter dollies constructed on or after March 1, 1998. On the left side of these dollies will be a yellow light.
  • Lighting: Dollys must have two reflectors, one stop light, and one tail lamp. Rear turn signals and danger warning flashers should be installed on every converter dolly.
  • Suspension: Dollies will either have a mechanical spring suspension or an air ride suspension.

Conversion Dollies’ Several Types

Converter dollies come in two different varieties.

Their drawbars set them apart.


A single drawbar with a single, centralized hitching point is featured on the A-dolly.

The most popular kind of converter dollies used in the United States are single axle dollies.


Two distinct connections are side by side on the C-dolly.

This dolly, which is Canadian in origin, enhances the stability of various trailer combinations.

Why Use A Converter Dolly?

Converter dollies are helpful for swiftly shifting a lot of different loads.

Heavy-duty vehicles can carry higher weights, but there are rules that must be followed while transporting this much more cargo.

Trucks may only tow two trailers on public roadways in the United States.

Triples are only permitted in less populous states, even if several states permit them.

Triples are sometimes employed in less-than-truckload (LTL) freight transportation.

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Written by Bob Matsuoka
Bob Matsuoka is a blogger and founder of RVing Beginner blog. He has been blogging for over five years, writing about his own family’s RV adventures, tips for people who are interested in buying an RV or taking their family on an adventure by RV.