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Steering towards safety

Search ‘truck tyre blowout’ on YouTube and you’ll find a number of confronting clips. Most show what happens when a truck steer tyre suddenly ruptures or deflates, the consequences being catastrophic.

While tyre failure isn’t the most common cause of heavy vehicle accidents, it is a factor that stands out as being on the rise according to NTI’s latest research.

The 2019 NTARC Major Accident Report revealed an 80% increase in claims and incidents resulting from mechanical failure losses, with steer tyre failure being the predominant underlying cause.

It’s a concerning trend, says the report’s author Adam Gibson, and worth examining closely.

“It's worrying because until now, we have seen a downward trend in the proportion of mechanical failure losses,” Adam says. “Although at 6.5% of NTI’s large losses, mechanical failure only represents a small proportion of claims. What stood out is that of all of the tens of thousands of components that can go wrong with a truck and trailer as they travel down the road, over half of that 6.5% was linked to steer tyre failures.” 

Adam is quick to point out that the issue is not related to the tyres themselves or tyre manufacturers. The problem, he says, is largely due to tyres that are insufficiently inflated for the weight they are carrying. This is made worse by regulations which discourage the use of twin-steer prime movers, having only two steer tyres rather than four increases the risk of an accident should a single tyre fail.

 “When a tyre is underinflated, driving down the road and keeping multiple tons off the ground it generates a lot of heat,” Adam explains. “With less air pressure the tyre flexes more, so the rubber heats up in the carcass of the tyre to the point where the tyre loses its structural integrity and literally explodes.

“Based on the incidents we're seeing it appears to happen often in the corner, when the load increases as the truck turns,” he says. “All of a sudden rather than continuing on a curve, the vehicle shoots off in a straight line and leaves the roadway.

“In other words, when steer tyres fail, they tend to fail catastrophically,” Adam says. 

So, what can be done to help prevent steer tyre failure and the potential for a major accident? According to Adam, underinflated steer tyres is a risk that drivers, transport companies or operators and mechanics should all be aware of. Ultimately, he says, responsibility lies with the company to implement systems, processes and tools that ensure steer tyre pressure is regularly checked.

“Companies should have clarity around who is responsible for steer tyre pressure,” Adam suggests. “NTI strongly encourages operators to have a pre-start check that includes steer tyre pressure and include this in weekly workshop inspections.”

General tyre checks and maintenance are an important part of heavy vehicle safety yet can sometimes be overlooked. Adam says it’s vital that operators and drivers understand the distinct risk that steer tyres present, from a safety and financial perspective.

“If a tyre somewhere on a trailer lets go it might put the vehicle out of service and cost you $2,500 in lost productivity and a roadside tyre service,” Adam says.

“If a steer tyre lets go on a truck, it might result a prime mover and b-double trailer set that’s up to half a million dollars and weighing 60 tonnes leaving the road at high speed, posing a serious threat to the driver and other road users.”


Steer tyre tips

  • Most tyre manufacturers provide specific guidance and data on inflation of their tyres. 120 psi is a common measure but it’s worth checking with the manufacturer. As a general rule, the tyre pressure will be largely proportional to the weight. If a tyre is loaded to its maximum carrying capacity then tyre pressure should also be at the maximum inflation pressure. 80% load capacity means 80% tyre pressure and so forth.
  • It’s not a set and forget process. Steer tyres should be visually checked once a day and once a week with a high-pressure gauge.
  • Treat steer tyres as a special case, if they fail the results are far more likely to be catastrophic then if a one of twelve tyres in a triaxle group on a trailer lets go.
  • There should be clarity on what the expectations of the driver are. If he/she is expected to do nothing at all, just arrive and hop in the cab, then the responsibility shifts to whichever party is responsible for the maintenance of the vehicle.  This needs to be clearly communicated to all parties, if it isn’t documented that someone else is responsible for checking, then it’s safer to check it yourself.