PowerTorque Technical Guru, Bob Woodward, looks back to some important changes and the effect of design changes around the converter dolly conundrum.

Rewind to 1994, my first experience with air suspension converter dollies! Tri axles? It wasn’t good with pitching and diving, but after many alterations it performed okay.

Then in 1996 a client wanted air suspension on everything that transported their product, hence a new design phase – rigid drawbar air suspension converter dollies. Although this design was an operational success, operators did not embrace the concept; old habits are difficult to change.

Fast forward to 2018, where members of the Industry Technical Council (ITC) were discussing issues with tandem air suspension converter dollies, poor tyre wear and somewhat unpredictable dynamic handling.

Sometimes one needs to help oneself, in this example there was a safety and maintenance issue. From those discussions a project was born to develop an industry prototype.

With the support of ITC supplier members, the project progressed and the industry prototype rigid drawbar converter dolly was displayed by MaxiTRANS at the 2019 Brisbane Truck Show. This dolly was available to ITC members and the supplier clients for trialing. Its first trip in May 2019 was to Darwin where the first user report was, “this is fantastic”.

The rigid drawbar was a collaborative response to a problem for the betterment of all. Operators and manufacturers have been able to access the project experience outcomes with minimal operational risk.

Following are operator comments:

Tony McGrath – McGrath Newcastle:

“The decision to go with a rigid drawbar with the PBS A-double was significantly influenced by the ITC converter dolly on display at the Brisbane Truck Show in 2019. Discussions with the engineering team at MaxiTRANS convinced me this was the best option for the future A-double container skeletal operation.

“The tyre wear has been fantastic. I’m embarrassed to tell people that the first dolly is still on original tyres at more than 407,000 kilometres.

“When asked if there were any negatives, the only issues are the potential for increased wear in the coupling when operating on steep driveways and across kerbside gutters where one axle may clear the pavement at low speed – a similar situation occurs with all multi-axle groups.

“Our drivers appreciate the dynamic tracking performance, braking and handling is excellent.

“The A-double and rigid drawbar converter dolly has been a great addition to the McGrath Newcastle operations.”

Image: Bob Woodward

Kel Baxter – Kelvin Baxter Transport:

“I was ITC chairman when the group embarked on this project and also had the privilege of trialing the prototype dolly. In my operation it was a game changer, to the extent that I have not purchased a hinged drawbar tandem converter dolly since. However, all the new dollies are PBS only to meet the axle spacing requirements of Victoria.

“The rigid drawbar dolly tyre wear is even across both axles, as it should be. PBS mandates airbag suspension and we found the supposed load sharing with a hinged drawbar resulted in issues with pitching under braking, resulting in excessive and uneven tyre wear on the lead axle.

“Perceptions of weight transfer and wear to the pin coupling are unfounded. The elimination of drawbar bushes is a maintenance plus.

“The excellent handling characteristics of the rigid drawbar dolly make for a much safer multi combination configuration. Drivers are rapt, saying that these 30 metre A-doubles handle and manoeuvre at least as well as a B-double. The combination of a fixed drawbar dolly and EBS brakes makes for a safer High Productivity Freight Vehicle to handle the task.

“Often tri axle dollys are used for their better handling characteristics and in many instances not carrying tri axle weights. A fixed drawbar dolly is a great alternative.”

Laurie Brothers – Ron Finemore Transport:

“My first experience with rigid drawbar converter dollies was in car carrying road train operations (doubles and triples) in 1996. The immediate benefits were tyre wear and dynamic handling, especially when braking.

“These were also then introduced to other operations. In car carrying, where the coupling height needed to be much lower than standard, this proved to be a dynamic benefit as the resulting coupling height was close to the trailer suspension roll height, limiting input into the dolly due to trailer roll.

“Some 20 plus years later other operators recognised the benefits of the lower coupling height. The drivers appreciated the improved performance, especially on narrow road sections with sharp shoulders.

“Now RFT has rigid drawbar tandem converter dollies on fuel haul operations 30 metre PBS A-doubles. Operating both standard height couplings and low height couplings, drivers report a preference for the lower height coupling.

“Suspension, axles, brakes and fifth wheel maintenance is similar to that of a B-double tandem lead trailer.”