The study to look into the viability of super single tyres is an important one when it comes to supporting the move to zero emission vehicles across the industry.
“Super Single wide tyres are an important topic because the next innovation or change coming to our industry is probably going to be in the form of zero emission vehicles, battery electric or hydrogen powered,” says Anthony Germanchev of the Australian Road Research Board.
“What’s the barrier to that coming to fruition? It is the pavement science.
“The fact is they need heavier steer axles and the methodology that we used in this project can be applied to that use case as well.
“The motivation for this project was the benefits that are available on the current vehicles, and to right some wrongs, as well. What did we actually test? We had two subject tyres, the Michelin 445 and 385.
“Then we had reference tyres, a dual set which is the 11R22.5, the most common tyre used. Then we picked the worst case as well, based on what we thought was the narrowest dual tyres you can put on a vehicle today, the 255.
“There is now a published report, and this is where the lobbying and the advocacy work begins. We are now working towards changing the regulations.”
The trailer used on the testing belongs to the NTRO. This is fitted with a rig which can apply a number of forces. It can apply any vertical force, horizontal force, turning angle, tractive force and camber angle needed to generate the kind of force that is going to be applied on our pavements by trucks and trailers.
The system produces a pressure map of the tyre’s footprint. The testing included tyres at varying pressures. The team were looking for the correct sized footprint, ideally with an even spread of pressure over the footprint. This ideal is the footprint of a tyre which does the least damage to the pavement.
When the team compared the images they took of the tyres’ footprint, over inflated tyres produced a small footprint with the pressure concentrated in the middle of the footprint. For correctly inflated tyres, the pressure was evenly spread over a wider area, reducing road damage.
The rig which runs the tyres over the road surface in the testing sees the tyre running up and down over a 12 metre section of pavement at about 20 km/h. With this system it is possible to replicate the loading on real pavements in a very short period of time.
The test team built the new pavement in their testing facility. On top of the stabilised clay there was 600mm of what is known as an unbound granular pavement.
“Granular means the road has no binder, it’s not glued together with bitumen,” explained Anthony.
“It is just crushed rock compacted and the aggregate size and shape is very important. Then it’s sealed with a thin seal over over the top. That’s what makes up 80 to 90 per cent of our roads in Australia.
“This test road represents the most common road and our weakest roads, the roads in local government, rural areas. Everything apart from major highways are built that way.
“We marked it up to replicate 12 pavement sections that were identical and then we could do reference tests between all of them.
“The machine itself has a lateral or dithering motion that it performs, replicating the fact that a vehicle is not going to just track down the same path every single time in real life. There’s a pattern that starts in the middle, then moves a little bit to the left and right.”
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