Is It Time to Mandate CTI for PBS Vehicles?

Weighing the Pros and Cons for Braking and Stability Compliance

As Australia’s Performance-Based Standards (PBS) scheme matures, the spotlight has intensified on the systems and technologies that enable heavy vehicle combinations to meet its stringent performance thresholds – particularly in the domains of braking efficiency and dynamic stability. Among these, Directional Stability Under Braking (DSUB) and Static Rollover Threshold (SRT) remain two of the most critical and technically demanding standards, often pushing vehicle design and configuration to the limits of conventional engineering.

Within this high-performance context, Central Tyre Inflation (CTI) has emerged as a potentially transformative technology. By allowing real-time adjustment of tyre pressures based on load state and road conditions, CTI offers a pathway to maintaining optimal tyre contact, consistent brake balance, and improved lateral stability across variable operating scenarios. The potential of CTI to significantly enhance braking and stability in PBS vehicles is a reason for optimism in the industry, promising a future of improved vehicle safety and performance.

But despite its benefits, CTI remains an optional fitment – not a mandated feature – within the PBS framework. This raises a critical engineering question: Should CTI become a compliance requirement for certain PBS vehicle classes or operating conditions, particularly where load variability and braking stability margins are tight? Or is its complexity and cost better reserved for niche or high-risk applications?

This article examines the technical merits and operational constraints of CTI through the lens of PBS braking and stability compliance – weighing whether it should evolve from a performance enhancer to a formal regulatory requirement.

There is no question that Australia’s Performance-Based Standards (PBS) scheme has revolutionised the heavy vehicle landscape, allowing innovative vehicle designs that deliver greater productivity and safety through performance-based rather than prescriptive criteria.

Before diving into the role of CTI, it’s essential to understand what PBS requires. Braking and stability performance for PBS vehicles is assessed through criteria such as:

• Directional Stability Under Braking (DSUB): The vehicle must decelerate rapidly from 60 km/h without deviating from its lane or experiencing gross wheel lock-up.
• Static Rollover Threshold (SRT): Vehicles must have a minimum lateral acceleration threshold before rollover (typically ≥0.35 g).
• Yaw Damping and Rearward Amplification: These ensure the vehicle doesn’t exhibit excessive sway or trailer whip during high-speed manoeuvres.
• Brake Balance and Load Proportioning: Brake forces must be well distributed across all axles to avoid skidding or instability, especially in lightly loaded conditions.

These standards are assessed using dynamic simulations or physical testing and often rely on precise tyre modelling, axle load data, and friction assumptions – making tyres and their inflation pressures a paramount consideration.

Understanding the Role of Tyre Pressure in Vehicle Performance

Before we delve into the role of CTI, it’s important to recognise the direct impact of tyre inflation on vehicle performance.

Tyre inflation directly affects the contact patch, which determines the tyre’s ability to generate traction under braking or lateral loads. A properly inflated tyre maintains optimal stiffness, heat dissipation, and tread engagement with the road. However, tyre pressure requirements vary significantly between fully loaded and empty configurations.

• Overinflated tyres, when unladen, can result in a reduced contact area, increased stopping distances, and less steering and braking grip.
• Underinflated tyres, when fully loaded, may overheat, deform excessively, and exhibit unpredictable handling characteristics.

PBS vehicles, particularly multi-combination units such as A-doubles or B-triples, often operate at drastically different load states on their outbound and return legs. The ability to adjust tyre pressure to suit these conditions is where CTI offers its most compelling benefits.

CTI System Overview

A Central Tyre Inflation system typically includes:

• An onboard air compressor (from truck engine).
• Rotating air seals at the hubs
• A driver interface to select road or load condition presets
• Sensors and controllers to monitor and maintain pressure levels dynamically

CTI allows drivers to reduce pressure on the fly when operating on unladen or rough terrain, and then reinflate the tyres to highway pressures when required. It’s widely used in military, off-road, and logging applications, but its adoption in linehaul transport – particularly under the PBS framework – is still emerging.

Advantages of CTI for PBS Compliance

1. Improved Braking Performance when Unladen

Unladen vehicles are often the most challenging to control during heavy braking due to reduced axle loads and high tyre pressures. CTI enables the operator to lower tyre pressures when unladen, increasing the contact patch and friction, which reduces stopping distances and the likelihood of trailer lock-up. This supports compliance with DSUB criteria, particularly in single-trailer or A-double applications.

2. Consistent Tyre Pressure Across All Axles

CTI ensures uniform and optimal inflation across all tyres – reducing the risk of brake imbalance caused by under- or over-inflated tyres on individual trailers. This is especially relevant for PBS vehicles with multiple articulation points, where imbalance between trailer units could otherwise compromise directional control.

3. Enhanced Lateral Stability on Uneven or Unsealed Roads

On mixed-surface routes – such as first/last-mile access roads in agriculture or mining – lower tyre pressures provide improved footprint and damping. This can reduce lateral sway, enhancing the vehicle’s and SRT performance under real-world conditions.

4. Load-Sensitive Pressure Control

When integrated with load sensors or pre-programmed logic, CTI can dynamically adjust inflation to match the gross combination mass (GCM). This supports load-proportioning brake systems and contributes to brake balance – another vital aspect of PBS compliance.

5. Reduced Tyre Wear and Heat Generation

By avoiding overinflation on unladen trips or underinflation when loaded, CTI can extend tyre life, reduce rolling resistance, and prevent heat build-up that can degrade braking response.

Limitations and Challenges

Despite the above advantages, CTI is not without trade-offs.

1. High Installation and Maintenance Costs

A typical CTI retrofit can range from $10,000 to $25,000 per vehicle combination. Ongoing maintenance involves checking air lines, seals, and hub assemblies –adding complexity to workshop operations. While some operators may argue the initial cost may be difficult to justify unless operating in high-utilisation or off-road conditions. But seasoned CTI users are quick to quell that theory, with documented evidence overall cost of life reductions because CTI increased tyre life, reduced tyre failures, reduced overall vehicle combination maintenance and importantly, improved safety.

2. Limited Effect on Fully Loaded Braking

When PBS vehicles are fully laden, tyres are usually already inflated to optimal pressures. CTI provides no additional braking advantage in these cases and may be redundant from a performance perspective.

3. Integration Challenges with Existing ABS/EBS

CTI must be carefully integrated with ABS and EBS systems, which rely on tyre stiffness and pressure for calibration. Mismatches between expected and actual inflation can impact brake modulation and system responsiveness if not correctly mapped.

4. Lack of Regulatory Incentives

However, at present, CTI is not recognised as a formal compliance pathway within the PBS scheme. While some industry proposals have floated the idea of CTI as a “deemed to comply” method for tyre performance, this has not been adopted by the NHVR. As such, operators receive no regulatory benefit or shortcut for CTI investment.

5. Limited Operator Familiarity and Support

Training and familiarity with CTI systems remain low among many linehaul operators, and support infrastructure (such as workshop tools and spares) may not be readily available outside niche sectors like forestry. But CTI manufactures state training is readily available, and the systems are user friendly.

Conclusion: Is CTI Worth It for PBS Operators?

CTI presents a technically robust and operationally flexible solution to many of the tyre-related performance challenges faced by PBS vehicles, particularly those operating under variable loading conditions or on diverse road surfaces. It enhances braking effectiveness, supports stability metrics, and delivers broader benefits in tyre management and ride comfort.

However, the cost, integration complexity, and absence of formal PBS incentives remain significant barriers. For operators running high-utilisation PBS combinations – especially in industries like agriculture, logging, and regional freight – the return on investment may well justify the added complexity. But for metro-based fleets with consistent loads and high-speed sealed-road usage, the gains may be marginal.

As PBS standards continue to evolve – and as regulators begin exploring load-responsive technologies – CTI may well earn a more prominent role in the future. For now, it remains an innovative, optional technology that offers real benefits to operators willing to invest in precision, safety, and compliance beyond the minimum standard.

Case Study: Beating the Desert with CTI Smarts

With Fleet and Logistics Manager Brian “Spud” Murphy

In the unforgiving expanse of Australia’s Red Centre, where road trains pound across scorching gravel and tyre failures can spark disaster, the difference between success and catastrophe often comes down to the smallest detail – air pressure.

For Fleet and Logistics Manager Brian “Spud” Murphy, running fuel into the remote Tanami goldfields wasn’t just another transport job – it was a high-stakes logistical operation demanding precision, foresight, and bulletproof reliability. At the heart of his strategy was Central Tyre Inflation (CTI), a technology he credits with transforming both performance and safety for his triple road train combinations.

In this exclusive case study, Spud takes us inside the real-world challenges of hauling volatile fuel across 1,800 kilometres of some of the most hostile terrain on earth. From cutting tyre temperatures and reducing suspension stress to eliminating blowouts and improving driver safety, his firsthand account reveals why CTI became more than just a system – it became a mission-critical asset.

The Road Less Forgiving

The run from Darwin to the remote Tanami goldfields spans more than 1,800 kilometres. Fuel road trains rumble 1,400 kilometres down the Stuart Highway before swinging west onto the dusty, corrugated Tanami Track – a road that chews up tyres, pulverises suspensions, and leaves no room for mechanical error.

“Our fuel tanker road trains had CTI fitted throughout the entire combination,” Brian begins. “That includes the steer, drive, and trailer tyres. When we left Darwin fully loaded, the 385 steer tyres were at 105 PSI. We had nearly seven tonnes over the front axle. Drive and trailer tyres were set at 90 PSI.”

This isn’t just about air pressure – it’s about strategic survival.

As the road trains near the Tanami turnoff, the real magic begins. “We’d flick the CTI dash controller and start deflating tyres before we hit the dirt,” Brian explains. “Steers down to 85 PSI, and drives and trailers down to 50 PSI. We had the CTI integrated with MTData, and we’d geofenced the Tanami Road. If a driver went over 60kph on the dirt, we’d get an alert instantly.”

Performance Meets Protection

The CTI system enabled precise real-time tyre pressure adjustments, dramatically reducing harsh vibrations and protecting the chassis and suspension from excessive stress. Hendrickson engineers took a closer look when the team started experiencing premature suspension bush wear. “They mounted strain gauges on two trailers and tracked the loads. When we deflated the tyres from 90 to 50 PSI, the reduction in strain on the trailer chassis was immediate and measurable,” Brian says. “There was a huge difference!”

But it wasn’t just about chassis wear. The road was wreaking havoc on the suspension system, particularly the shock absorbers. “Standard shockers couldn’t handle the punishment – we were lucky to get two or three trips out of them,” Brian recalls.

Enter King Shocks. Their engineers were astonished at what they saw. Potentiometers and linear sensors revealed just how violent the inputs from airbag suspensions were under load. “We recorded shocker temperatures up to 160°C. The airbags were reacting so fast it shocked even the engineers,” he recalls.

CTI: A Safety Investment That Pays

Amid all the technical advantages, one benefit stood head and shoulders above the rest – safety.

“We didn’t have any tyre failures once CTI was installed,” Brian says firmly. “That dramatically reduced the risk of tyre fires – a critical concern when you’re hauling volatile fuel through the desert in 45-degree heat. With CTI, if a tyre loses pressure, the driver gets an instant alert in the cab. That’s not just protecting drivers and equipment – it’s safeguarding every other road user too.”

The system’s impact extended far beyond safety. Reduced heat buildup, lower carcass stress, and improved footprint traction meant tyres lasted longer and were less prone to catastrophic failure. “The increase in tyre life and reduction in equipment damage were welcome bonuses, but for us, it was the safety gains that justified the investment.”

Lessons from the Red Heart

Brian’s Tanami experience underscores the broader lesson for fleet operators running in extreme conditions: CTI isn’t a luxury – it’s a necessity.

Across the country, operators in remote mining, pastoral, and infrastructure sectors are quietly adopting the technology, recognising the gains in reliability, cost savings, and safety.

As compliance requirements around Chain of Responsibility tighten and equipment replacement costs skyrocket, systems like CTI aren’t just helping trucks survive the desert – they’re redefining what smart outback logistics looks like.

Brian’s experience underscores a clear case: if CTI delivers such proven safety and durability in the harshest conditions, should it now be mandated for high-risk PBS operations?

Special thanks to Brian “Spud” Murphy for his assistance compiling this article.

Author Note:

This article is based on NHVR guidelines, PBS technical assessment standards, and recent industry research into tyre pressure and braking dynamics. For further information on CTI integration or PBS performance modelling, consult an NHVR-approved PBS assessor or visit www.nhvr.gov.au.

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