ARTSA-I recently held a meeting about Tyre Monitoring Systems (TMS). I want to consider the international mandates, the state of this technology, and consider whether it should be adopted in Australia.
Tyres provide the interface between the heavy vehicle and the road. Tyre condition and characteristics are important factors for safe road handling, ride quality and fuel economy.
In-cabin monitoring of tyre pressure and temperature is now proven and should be considered as standard equipment on heavy vehicles.
The step up to autonomous central tyre inflation is viable and sensible considering the proven benefits to the operator of managing tyre air pressure to achieve optimum road handling, improved tyre life and to reduce rolling resistance.
The European requirements are based upon UN ECE Regulation 141 Uniform provisions concerning the approval or vehicles with regards to their Tyre Pressure Monitoring (TPMS).
The UN ECE regulations are not law. Countries that participate in the UN ECE project, such as Australia, can decide to adopt all or part of the model regulation into its law.
The European Union adopted this regulation for new model approvals of commercial motor vehicles and heavy trailers starting in July 2022 and for all new registrations from July 2024.
The requirement is that these heavy vehicles have a functioning Tyre Pressure Monitoring System.
That is, a system that alerts the driver via, at least, a warning lamp in the cabin when the air pressure in any tyre on the combination vehicle falls below a present level.
The alert, which could be a single warning light, can take up to eight minutes to be given. Higher level systems display and record individual tyre pressures and temperatures.
Regulation 141 also describes the technical requirements needed for a Tyre Pressure Refill System. The EU did not mandate this feature.
The TPRS system must be able to refill a tyre within 10 minutes of an alert occurring.
The air pressure for the tyre may be delivered to the wheel hub internally via the axle or externally. In both cases a pneumatic slip joint is required. The tyre receives the air pressure from the supply point via a short length of tube that is connected to the valve stem.
For dual tyres the pressure tube loops between each valve stem.
Several European and US axle suppliers can provide TPRS systems that deliver air pressure to the wheel end via a ‘tunnel’ along the centre line of the axle. If the motor vehicle has a TPMS function, it can collect data from the trailer tyres via either the brake CAN data bus or by wireless communication.
Tyre pressure monitoring can be an integrated feature of a trailer EBS brake system, in which case the EBS manages the tyre pressure measurement data and communicates it to the motor truck via the CAN data bus.
If an older trailer has no TPMS then no CAN data is generated from that trailer and the cabin TPMS controller will ignore that trailer. Australia has effectively mandated EBS on new trailers in 2019.
The United States has mandated a TPMS function on light motor vehicles (GVM less than 10,000lb) since 2007. It is known as the ‘Tread Act’ (FMVSS 138) because it was developed in response to a spate of crashes due to tyre tread delamination on a specific tyre model.
The US TPMS function requires that a visual alert be made to the driver when any single tyre on that vehicle has a pressure less than the present level by 25 per cent or more.
US systems exist for the heavy vehicles, but they are unlikely to communicate data via a CAN bus because US manufactured trucks seldom have a brake CAN data bus.
The USA systems usually have the form of a pressure sensor that is attached to the wheel valve stem. The pressure measurement is transmitted wirelessly to a collector that in turn communicates with a module in the truck cabin. Such systems can display the individual tyre pressures.
TPRS systems are also available from US axle manufacturers for use on heavy trailers.
The US mandate does not apply to heavy motor vehicles or to heavy trailers and is unlikely to in the current political climate. There is also no Japanese mandate for Japanese made trucks.
There is much Australian interest in both TPMS and TPRS. The HVIA has developed a discussion paper relevant to TPMS on heavy vehicles, and this was both educational and persuasive.
While Australia has a policy of ‘harmonising’ its vehicle regulations with the UN ECE Regulations, Australia is cautious about adopting a new UN regulation when major supplier countries have not mandated the relevant function.
But this should not be the situation for trailers. Considering that Australia has more tyres on an average truck than any other country on earth, the advantages of tyre monitoring and pressure management are amplified.
LSM Technologies has developed a direct pressure sensor installed at each tyre and it collects pressure (and temperature) values and can both display them to the driver and enter exception levels into a fleet monitoring system.
Air CTI, also an ARTSA-I affiliated supplier, offers custom installed TPRS systems that displays pressures to the driver and allows the pressure level to be specified in the cabin and automatically set.
The reasons for installing both TPMS and TPRS are clear. Tyre pressure determines the shape of the loaded tyre.
The road handling forces are generated by the tyre in response to the direction and speed of the wheel versus the direction and speed of the truck.
Remarkably, it is not air pressure that supports the weight of the truck, it is the tyre sidewalls which should be the appropriate shape. The size of the contact patch of the tyre on the road determines how much of the road ‘roughness’ can be used during braking and acceleration.
The ratio of laden/unladen mass on a tyre determines how much tyre pressure should be reduced when the vehicle is unloaded.
For the drive tyres on a prime mover that ratio is about 2 or 2.5:1. For a semi-trailer with a triaxle group, that ratio could be 4 or 5:1. If an 11R22.5 tyre is inflated to 552kPa (80psi) on a laden vehicle, and the load is then removed, the contact patch on the road will probably be reduced by 75 per cent.
Considering a 4:1 mass change, the available road friction will be 15 – 20 per cent less unless pressure is altered.
Hence the emergency stopping distance will be substantially increased and the risk of jackknife or trailer swing during braking will be increased. The sidewall will become taller with no loss of side force capability.
On the other hand, if the tyre pressure was at the correct value for the unladen tyre, which is about 207kPa (30psi), and the vehicle is loaded to four times the tare mass, the road contact patch will be twice the optimum area, and the sidewalls will be floppy.
The vehicle is in serious risk of poor road handling due to loss of lateral force capability, and a significant fire risk arises. Heating of the tyre sidewall and rubbing together of dual tyres is likely to occur.
The tyre energy loss will be triple in this case. A common Australian practice is to drive with over inflated tyres as the least-worst option.
So most Australian trucks experience a 15–20 per cent deficit in optimal braking and road handling performance because the tyres are over-inflated when the vehicle is unladen. It is time for the Federal regulator to issue a notice of intention to mandate TPMS as defined in UN ECE R141 on new heavy motor vehicles by July 2028.
The Regulator should also mandate TPRS on new trailers based upon UN ECE R141 technical requirements. Australia manufactures about 90 per cent of its heavy trailers.
PRS systems are available from European, USA and Australia suppliers. Road safety and fire safety would be improved. The majority of drag energy losses on multi-combination vehicles comes from the tyres and a trailer life span is measured in decades.
Substantial greenhouse gas reduction can be achieved directly and indirectly by improved tyre lifespan. TPRS seems very sensible with wide based super-single tyres that mainly could be used on trailers.
There are compelling reasons to mandate TPRS, at least on new trailers by July 2028.
Peter Hart
ARTSA-i Chair
