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Chain of Responsibility

Adam Gosling - Thursday, November 02, 2017

How tyres form a safety critical link in the Chain of Responsibility for not only personnel in the supply chain but also the actual vehicle safety systems.


The Chain or Responsibility (CoR) is the overarching legal requirement that all parties in the supply chain from the consignor to the consignee have to ensure their legal responsibilities have been met.


There are accreditation systems that cover heavy vehicles, the WAHVAS, NHVR, Trucksafe come to mind. There are many compliance systems that cover driver accreditation and matters like fatigue, journey planning, load restraint, fault registers and mechanical maintenance.


All vehicles on our roads today have a common factor, all vehicles, heavy, light, electric, diesel and even autonomous vehicles, they all ride on pneumatic tyres.


How is tyre maintenance evidenced within the CoR? Already I hear many groans but consider that a vehicle can be overloaded yet under mass. So even if all the matters above receive a tick the vehicle can be deemed unroadworthy. How is this so?


Tyres 101 tells us a tyres prime function is to contain the air within the tyre's structure. We all know that a flat (no or low air) tyre supports no load. Let’s look at an 11R22.5 16pr tyre for instance, at 120 psi this tyre in a dual configuration will support 2,725kgs, that’s 10,900kg for an axle (4 tyres). At 100 psi the same tyre supports only 2,470kgs, that’s 9,800kgs axle load. That’s a 10% reduction in load capacity. A 295/80R22.5 goes from 3,150kgs @ 120 psi to 2,770kgs @ 100 psi, that’s a 12% reduction in load capacity. How many tyres are operating at the level they are actually required to be at?


So if the tyres are not appropriately inflated for the load (and speed) on the vehicle then the vehicle will be overloaded, yes even if it is under the rated GVM.


There are weigh in motion devices on trucks, engine control modules that regulate the amount of power a driver can apply, GPS and speed tracking devices and even cameras to see when the driver is getting droopy eyes. When I ask a driver to stop his truck, open the engine cover, remove the radiator cap and dip a thermometer into the coolant to check the engine temperature they usually break out into laughter, until I ask them how they check their tyres. Putting a manual gauge onto a tyre is akin to the process I’ve just outlined, last used in the 1930’s.


Tyres support the vehicle in more than just a load carrying capacity. Drive, steering and braking efforts are all applied through the tyres. If the tyre is underinflated the tyre will not perform as the designer intended, will the vehicle perform as the designer intended?


When we consider the chain of responsibility we generally only think of the people involved but let’s apply it to the vehicle for a minute. The steering wheel is connected to the steering shaft and steering box, which is connected to the linkages that rotate the wheels around an axis. The wheels have tyres. The engine produces the power that is transferred through the clutch into the transmission that reduces the speed and increases the torque that is transmitted to the differentials and axles to drive the wheels. The wheels have tyres. The trailer axles have brakes on the wheel end, which are applied by the driver as required, the brake shoes or pads engage with the drum or disc and convert the kinetic energy into heat energy reducing the speed of the wheel. The wheel has a tyre mounted. The tyre connects the brake to the pavement. The tyre is like the consignee; it is the last point of contact. It has the responsibility to transfer the steering, drive and braking forces from the vehicle to the pavement. Why is this not important? Tyres are absolutely critical in vehicle safety. ABS, ESC, all sorts of electronic wizardry all depend upon the tyre to transfer the forces without diminishment.


Tyres provide not only safety but great economics as well. Tyres are one of the largest operating expenses for a heavy vehicle. They are one of the most uncontrollable expenses as well. If a tyre fails catastrophically then the damage can be considerable, busted guards and lights, lost time in awaiting a tyre service even the total loss of the vehicle. How? Just think of a truck driver’s worst nightmare, a steer tyre failing whilst at top speed. How many single vehicle accidents are the result of a steer tyre failure?


The upside of maintaining tyres is manifold in that not just do the tyres themselves last longer but the wheel ends and bearings, the transmission and driveline last longer, fuel burn is reduced by a couple of percentage points at least. Even driver fatigue is reduced! WHAT? I hear screamed! Think of a tandem drive, 8 tyres all driving. If the tyres are at different pressures, then they’ll all be driving at a different rate. Imagine thjis tandem drive set-up wearing a running shoe, teamed with a work boot, a golf shoe, a football boot, a slipper, another different running shoe and a dress boot. How are these all going to work at the same rate? If the tyres don’t work as a team then the driver will be constantly redirecting the vehicle as each shoe, sorry tyre, imparts its own effort in driving forward or around a corner. After hours of constantly providing subtle inputs to the steering why would a driver not be tired and fatigued? The driver may well be fatigued before the driving hours are up, just as the vehicle can be overloaded but under mass.


Aah yes, the perennial statement of “our tyre service has set the tyres during the last service”. So what have the tyres experienced since? Even if the tyres were all set to the same cold pressure before the vehicle departed in operation the tyres would not be at the same pressure during operations. Inside tyres are deprived of the same cooling as outside tyres are, steer tyres experience higher loads on downhill sections and at higher speeds, drive tyres experience more load on uphill sections. Inside tyres experience the waste heat from the engine and exhaust emission systems, high horsepower trucks are even worse, add long range fuel tanks and the ventilation goes to nada, zip, zilch, and the tyres? They just keep working but they are getting hotter, increasing in pressure and size resulting in the outside tyres scuffing every revolution.


BPW Axles report that a 5 psi difference between a pair of dual tyres is worth a 10% reduction in bearing life, a 10 psi difference is worth a 20% reduction. Transfer this wear back up the driveline exacerbating wear along the way until the engine is working harder wearing parts out, burning more fuel.


Maintaining tyres in real time is a no‚Äźbrainer, just as modern trucks have electronic gauges to monitor pressures and temperatures to alert to engines or transmissions overheating so they can be fitted with real time tyre pressure monitors to display tyre pressures without leaving the driver’s seat, they can be connected to data loggers or telematics to provide historical evidence but more importantly data to drive positive economic outcomes.


Just as a fatigue log book can evidence a driver’s work, an ECU can be downloaded to reveal the speed and driver attributes so tyres can be monitored and evidenced. The chain of responsibility does not stop with humans, it extends all the way through the vehicle, from the consigner the engine, to the consignee the tyres.


How do you evidence your chain of responsibilities? How do you keep your safety record in tact?  How do you maximise your bottom line?




If your tyres aren’t turning, they’re not earning©. We aim to keep them turning for longer.