Research fully supports adoption of wide single tyres
In a milestone media release, the Truck Industry Council (TIC) and National Heavy Vehicle Regulator (NHVR) have stated “there is no justification in limiting axle masses when using appropriate wide single tyres given the improved vehicle stability and efficiency they bring. They should be permitted to operate at the same mass as equivalent dual tyred axles”.
While wide single tyres (also knowns as super singles) have been around for decades internationally, adoption locally has been hindered by fears around the wear impacts they may have on Australian roads, particularly sprayed sealed pavements.
Due to these concerns, the Heavy Vehicle National Law (HVNL) stipulates that most axle groups fitted with wide single tyres cannot carry the same load as their dual-tyred counterparts. Furthermore, wide single tyres are not eligible for selection on Higher Mass Limits (HML) nor Quad-axle Mass Limits (QML) because they are not deemed ‘road-friendly’, a designation held only by dual tyres. A qualification to this, as of May 2023, is that PBS quad-axle semi-trailers fitted with wide single tyres can now operate at up to 24 tonnes at HML in Queensland. While positive news for industry, there is still a 3-tonne payload deficit to quad-axles fitted with dual tyres. The net result of these restrictions is that existing regulations discourage the adoption of wide singles tyres into the national fleet.
To better understand the impact of wide single tyres on Australian roads, a testing program was conducted using the National Transport Research Organisation’s (NTRO) Accelerated Loading Facility. In collaboration Michelin and Goodyear, nine identical pavements were constructed with each repeatedly loaded to determine the relative pavement wear for various tyres.
The results revealed that the pavement deformation rates for both dual and single tyres were within a similar range. Furthermore, it was found that pavement wear caused by wide single tyres was less sensitive to inflation pressures than duals.
“Taking a real-world perspective on the comparatively small differences in pavement wear found, the pavement damage exhibited by the commonly used 11R22.5 dual tyre configuration was notably influenced by inflation pressure, with the highest damage observed when these tyres were over-inflated – a common occurrence in practice” explained TIC Technical Officer Paul Caus.
“In addition to the finding, day-to-day use of single tyres make it easier for drivers to check tyre conditions, monitor inflation pressures, and inspect brake components reducing the risk of overheating brakes and wheel end fires.”
“TIC’s view is that there is no justification in limiting axle masses when using appropriate wide single tyres given the improved vehicle stability and efficiency they bring. They should be permitted to operate at the same mass as equivalent dual tyred axles.”
Advantia has been engaged in multiple projects studying wide single tyres and fully supports TIC’s conclusions. Solely from a vehicle dynamics perspective, wide single tyres can enhance stability, and therefore safety, through wider track widths. Wider tracks also allow for suspension to be constructed with wider lateral spring spacings, which increases the roll stiffness of the suspension. This means that handling performance is improved, while rollover risk is reduced.
The NHVR’s chief safety and productivity officer David Hourigan welcomed the report’s conclusions, remarking “the findings of this report will be of great importance to equip road managers and the NHVR with the knowledge needed during consideration of vehicle load limits and the benefits provided by super single tyres”.
With the benefits widely recognised, and the pavement wear impacts revealed to be minimal, it should only a matter of time before suspension using wide single tyres is recognised as ‘road-friendly’. For more information, contact Advantia today.