Australia's very long drawbars

A Mack truck pulling a dog trailer in Australia. Photo: Grays Auctioneers

A common sight in Australia is a three-axle truck with a very long drawbar pulling what Aussie truckers call a Dog Trailer.

Overseas drivers always ask why waste all that space between the truck and trailer using a drawbar that is up to 4.5 metres long? 

The answer is that the long drawbar is specifically designed to allow jackknifing the trailer at the dump site, as show below in a drone video by Brisbane-based Tactical Aerial Solutions: 

After dumping the trailer load, the driver continues to reverse the trailer with quarter turns on the steering wheel until the trailer is parallel to the truck, which can then dump its load neatly next to the trailer's load.

While the long drawbar allows for neat dumping, it can quickly suffer metal fatique along the welds and bolts. This damage appears as very fine cracks which are difficult to spot, but drivers look for fine lines of red rust that will only show on critical points after a washing the drawbar.  

The length of the dog and trailer is limited to 19 metres (compared to South Africa's 22 metres) and while the long drawbar does limit payload space, it makes for a very stable trailer. 

The long drawbar also allows Australians to build trucks that look like nothing else on earth, with the sleeper cab often as big as the load bin!

Only in Australia: A 2014 Freightliner Argosy 6x4 Sleeper dump truck configuration. (Photo: Ritchie Bros Auctioneers)

The maximum combined mass of these combinations is 43.5 tonnes, although quarry and mines operators often get a permit to exceed this, national limit, loading "Quad Dog" trailers (with five axles), or "Quin Dogs" (with six axles) with many tonnes more. 

A 2017 Kenworth K200 Big Cab Aerodyne dump truck configuration. (Photo: Ritchie Bros Auctioneers)

(Written for SATrucker's weekly World Trucks series.)