With fuel prices rising to record levels, farmers are looking at ways to ensure they get the most bang for their fuel buck. One excellent way of reducing fuel expenditure while also improving productivity is to ensure that tractor tyres are inflated to the optimum pressure, says Stephan van Staden, National Agricultural Specialist at Bridgestone, manufacturer of Firestone’s portfolio of specialised agricultural tyres.
“Tyre management can yield huge benefits for farmers both in fuel efficiency and the performance of the tractor itself. Tyres account for between 20-40% of horsepower loss, and a huge factor is the pressure to which the tyres are inflated in relation to the load carried by the tractor,” Mr Van Staden says. “Getting this right requires some work, but it is well worth doing.”
The key principle is the importance of ensuring that the right amount of tyre surface engages with the working surface (the footprint). Aside from the load carried by the tyres, a key factor affecting the footprint is the tyre size. If a tyre is overinflated, it will have too small a footprint: there will be excessive wheel slippage, and the fuel consumption will be higher than necessary. In addition, the tyre will wear down quicker, and so will need to be replaced sooner.
Underinflated tyres will have too large a footprint, and there will be too little slippage. The result will be damaged sidewalls, atypical wear patterns and even the possibility of drivetrain breakdowns.
Farmers need to master the technique for calculating the correct tyre pressure for the job at hand. The easiest method is to use the static load radius (SLR) as the basis. The SLR is the distance between the centre point of the axle hub on the rear wheel and the ground. This measurement is provided in the tyre’s data book. By measuring the SLR with the tractor fully loaded, it is simple to see whether the tyre is over- or underinflated.
If the SLR is between 50mm and 100mm shorter than advised by the manufacturer, then the tyre is underinflated or the load is too heavy. To rectify, the tyre can be inflated (though never more than 160 kpa). If the SLR is still not ideal, the load is too heavy for the tyres.
On the other hand, if the SLR is too long, the tyre is overinflated and can be deflated until the correct SLR measurement is reached.
The closer the SLR is to the value in the tyre’s data book, the better the tractor will perform, and the longer the tyre will last.
Front tyres should be inflated to the same pressure as the rear ones, plus 20kpa.
Once this exercise has been done for a particular implement, a record should be kept so it does not have to be repeated.
“If the tractor has to spend less time in the field to get the job done, consumes less fuel and its tyres last longer, considerable savings can be achieved over a season,” concludes Mr Van Staden. “This is an often-neglected area—farmers can contact their Bridgestone supplier for more assistance in ensuring their tractor tyres are optimally inflated, and put themselves on track to realise all the benefits that follow.”
