PBS Tyres – Have we thrown the baby out with the bathwater?

by admin

PBS Tyres – Have we thrown the baby out with the bathwater?


PBS Tyres - Have we thrown the baby out with the bathwater?

On the 2nd of August 2021 the NHVR announced that Australian Transport Ministers had accepted the NHVR proposal to move to a generic PBS tyre (NHVR announcement), the Transport Minister’s meeting was on the 28th of May 2021. PBS operators and suppliers rejoiced at the news that the pain associated with PBS tyres would soon be gone after more than a decade of failed stakeholder discussions and policy proposals.

The detail of how and when PBS tyres will be deleted from PBS approvals is still unclear. The NHVR has promised to consult with PBS users in September about implementation arrangements. Given that it took over 2 months to report on the outcome of the Transport Ministers meeting we could well be waiting a further 6-12 months until the PBS tyre change is fully implemented.

So, for now, operators are still required to fit specific tyres according to their vehicle approval.

Change was necessary because the NHVR failed to absorb the complexity associated with assigning specific tyres to vehicles. The confusion, cost and inconsistencies with the current system became impossible to justify.

Numerous options were put forward to try and resolve the issue, but it was impossible to find agreement within a diverse stakeholder group with competing interests and agenda. The NHVR waived the white flag and opted for a generic tyre approach which greatly simplifies PBS.

The NHVR argued that the specification of tyres on PBS vehicles was not a factor in the impressive PBS safety record of PBS vehicles.

Now, when completing computer simulations of PBS vehicles, we will no longer use the data obtained from recent testing. Instead, Assessors will use the test data from a discontinued 11R22.5 tyre which was published in a 1986 study. The rationale is that this was the tyre data used when the performance standards levels were set nearly 20 years ago in 2002. This means that tyre cornering performance testing will no longer be required, even though few tyres tested had performance comparable to the generic.

The NHVR plans to develop a method for adjusting the generic tyre data to accommodate different tyre sizes based on load rating. This will presumably mean that smaller tyres will be assumed to have less cornering stiffness. How much less stiffness, and what this sliding scale of adjustments will mean for vehicle design is unknown.

It may result in all PBS vehicles being incentivised to fit smaller tyres to lower centre of gravity height as they do in New Zealand. Smaller tyres can reduce tare weight, but they can also increase rolling resistance and tyre wear. As always, the devil is in the detail, and only time will tell what unintended consequences arise from the change to how PBS tyres are managed.

The current system had to be simplified so that operators didn’t have to deal with the complication and cost of managing PBS Approvals with specific tyres. However, requiring suppliers to test tyres mostly at independent test facilities provided useful insight into how tyres behaved and the characteristics of a quality tyre.

Test data showed that poor performing tyres were often comparable to better tyres up to their rated load, but cornering performance tapered off during high-speed manoeuvres where load transfer generates forces up to twice the tyre load rating. When armed with this information, many tyre suppliers (mainly new entrants from China) re-engineered their tyres to achieved superior cornering performance across the load range to sell more tyres under PBS.

Unfortunately, this type of innovation is likely to end with the proposed changes to PBS tyres.

Have you read our last article? Do operators need PBS if they have a Road Train Prime Mover?