Making Tyres Last The Distance
Taking steps to protect and preserve off-road tyres will help improve safety and can increase productivity, explains Jack Dutcher, manager of off-road training and development with Bridgestone North America
Anyone using off-road tyres in their operation will be well aware that there is a gap between the demand for tyres and available supply. Two questions usually arise when that statement is posed to aggregate producers: Why?; and: How long will the shortage last?
The simple answer to the first question is that recent high demand for basic commodities, such as oil, gold, copper and iron ore, led mining companies to push for record levels of production, which, in turn, resulted in increased consumption of off-road tyres.
While the worst shortage has been in large off-road tyres, this situation has put pressure on all sizes of off-road tyres because of the associated support equipment demand. As a result, aggregate operations may also have had difficulty finding smaller off-road tyre sizes.
Additional off-road tyres are becoming available as new production commences and ramps up to full capacity, but supply may not meet demand for several years. So, what can aggregate operators do in the meantime?
The best thing anyone who uses off-road-tyres can do is maintain the tyres they already have and determine how to make those tyres last. This requires proper maintenance and a reassessment of operating conditions to better use those tyres. By following this strategy, operators will not only make their tyres last longer and reduce tyre costs, but will also see an improvement in overall productivity.
An effective off-road-tyre maintenance programme must include the following: an in-service inspection programme, an out-of-service inspection programme, a repair/retread programme and a continuous review of operating conditions.
Air pressure
Maintaining an off-road tyre starts with an effective air-pressure maintenance programme. Just as running an engine low on oil can damage the engine, running an off-road tyre with inadequate air pressure can damage the tyre.
It is the air within the air chamber of a tyre that actually supports the load of the vehicle and its payload. When a tyre does not have enough air pressure, it does not attain the correct shape in which the tyre was designed to operate. When ‘out of shape’, the tyre does not provide maximum traction, braking and cornering ability, nor does it flex where it was designed to flex, which causes heat and fatigue.
To make a tyre last as long as possible (and achieve the maximum production possible from the machine it carries), operators need to ensure the tyre is being used at its designed shape.
How can the exact configuration of a tyre’s designed shape be determined? First, determine the maximum load on the tyre (using the heaviest material, maximum load and maximum vehicle speed) and consult the tyre manufacturer’s load and inflation table. This table will indicate how much air pressure is needed to support that specific tyre load. While consulting this chart, it is worth noting how much carrying capacity is lost with a reduction in pressure of just 4–5 lb/in2. This range, which may seem minimal, is very significant to a tyre’s performance.
Once the amount of air pressure the tyre needs to provide maximum traction and cornering has been determined, it is necessary to take into account the fact that this air pressure is based on a ‘cold’ tyre.
To compensate for those occasions when someone has to check ‘hot’ tyre pressures, add 10–15% to the cold pressure and make this the expected hot pressure. If more or less pressure normally builds up during the work day, this should be made the target hot pressure.
Once the amount of air pressure actually needed has been determined, operators should stencil both cold and hot pressure levels on the hub or near each wheel position. This way, each operator will know what the target pressures should be and can adjust the air pressures accordingly.
However, the tyre should not be deflated too much until all possible causes of extra pressure have been eliminated (for example, heat from a dragging brake drum, excessive loads on one side of the vehicle or an air chuck left on too long).
Weekly checks
Once cold and hot pressure targets have been set, how often should air pressures be checked? It is important to understand that every tyre will lose some air pressure simply because manufacturers cannot make the inner liner of the tyre totally impervious to air migration.
To ensure that off-road tyres operate at the designed shape, air pressure should be checked and corrected at least once a week. By checking air pressure less often, such as every few weeks, operators run the risk of substantially reducing a tyre’s life, while also hindering the performance of the machine it supports.
It is also important to ensure that air-pressure checks result in air-pressure corrections. It does no good to check air pressures with merely the intent of correcting them later, since the correction may not happen.
Also, make sure that the tyre manager gets a copy of the inspection report, which shows what the air pressure was and what it was corrected to. The manger should compare the current week’s air pressures to those recorded the previous week, thereby identifying tyres that are constantly losing pressure and allowing corrective action to be taken.
Get everyone involved
Tyre management is critical to an operation’s success. Operators must know the condition of all off-road tyres and do something about the tyres that need attention. The first step in this process is to get all operators, mechanics and supervisors actively looking at the tyres used in the operation. If anyone finds any new damage/injury that is growing, it must be reported to the tyre manager to determine a course of action. The decision may be to leave the tyre alone or remove it for repair, or perhaps move it to another position.
Every damage/injury to a tyre must be considered for repair. Remember, tyres and rims are pressure vessels. Any weakness in either component can cause that assembly to come apart, often explosively. Just like the untreated human body, a tyre does not heal, it only gets worse over time.
Repairing off-road tyres is something that should be considered in every case, even if (at first glance) spending the money does not appear to be economical. If the tyre can be repaired and still provide a safe pressure vessel, operators should consider spending the money for the repair and keeping the tyre to one side for emergency use only. Then, in future, if a replacement tyre cannot be obtained, an emergency spare is always available to keep operations moving until a replacement can be found. This way, the investment in the repair will be repaid many times over.
Establish a committee
It is a good idea to establish a tyre committee – made up of production supervisors, maintenance supervisors and operators – for each quarry site. The group should meet regularly to spot-check tyres in service in the fleet. The committee should also inspect all out-of-service tyres (looking for things that can be corrected) to prevent losing another tyre to the same circumstances. Meeting with the local supplier and factory representative, when available, can go a long way toward bolstering tyre performance.
It is also important to review past decisions and how they have influenced the aggregate operation. On a regular basis, the tyre committee should tour the operation, looking at haul road curves and grades, and loading and dumping areas to determine what variables are putting undue stress on the tyres. Remember, variables that affect a tyre also affect machine durability and production. Key areas to watch out for are road crown in corners that produce a negative super-elevation, and excessive water on the road caused by water trucks.
An effective system of record-keeping is also important. The biggest challenge is forecasting off-road-tyre needs. Without accurate records detailing what kind of performance has been achieved in the past and what state current tyres are in, it is difficult to manage this asset. Bridgestone, as well as several other tyre manufacturers, offer tyre record-keeping software but whatever system is used, it is vital to keep detailed records.
Finally, before purchasing an off-road tyre that is different to the tyre normally used, seek advice on how this new tyre may affect the operation. It may be that the new tyre has a pattern with a higher likelihood of tread cut, or that the bias tyre being installed in place of a radial will slow down the vehicle. Understanding the potential ramifications of a purchasing decision is crucial, and this is where the local supplier or factory representative can help. Pick up the phone and ask questions. Operators are not alone in their quest to get the most out of their off-road tyres.
This paper is based on an article which first appeared in Quarry magazine and is reproduced here by kind permission.
