Driver Knowledge Tests

Pig trailer vs dog trailer vs jinker trailer vs dolly

A dog trailer has an axle set at both the front and back, plus a drawbar to connect the trailer to a towing vehicle. The front axle of the dog trailer has a drawbar connection and this axle steers. This means that a dog trailer can stand alone without legs, as would be required for a semitrailer. Only the drawbar has a leg or wheel for support.

5-axle dog trailer

A pig trailer has one axle set that is placed near the middle of the trailer. Most of the trailer’s weight is supported on this axle set as opposed to a semitrailer where some of the weight is supported on the fifth wheel. At the front, there is a drawbar which connects to the towing vehicle. The drawbar has a leg or wheel for support.

These boat trailers are effectively pig trailers as there’s only one axle set
This tandem axle trailer is a pig trailer. The majority of the weight is carried over the tandem axle, not the drawbar

Pig trailers are easier to reverse than dog trailers as there’s only one articulation point (the towing connection) as opposed to a towing connection plus a fifth wheel.

A jinker trailer is designed to carry longer loads. It consists of an axle set and platform or support with a connection to attach it to a prime mover. This connection can be anything from a short drawbar to a long pole, depending on the application. Longer jinker trailers are used to transport very long loads like wind turbine blades.

American logging truck carrying a jinker trailer, courtesy of Crispin Semmens

A dolly provides an interface between a semitrailer behind and a drawbar connection in front. As you can see with the logging trailer below, the rear trailer requires a fifth wheel, but the towing vehicle only has a drawbar connection. The dolly has the drawbar, while the rear trailer’s fifth wheel sits on top of it.

The dolly sits on the right of this picture, connected to the towing vehicle. The fifth wheel at the top is supporting the logging semitrailer.

Dollies are often used for shorter semitrailers that add capacity to a rigid heavy vehicle as required.

Darren is an expert on driving and transport, and is a member of the Institute of Advanced Motorists

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