Tyres have become some of the most expensive and sophisticated pieces of equipment on a farm. Yet people are still quite uninformed about how tyre pressure has an effect on the bottom line of the business.
You know how it goes: that ripper should have been running yesterday. When you take it out, you see that the tyres look somewhat flat. You grab the pump and pump them up until they look right. Now you are ready to plough.
This can, however, be very costly. You could waste up 40% of your tractor’s power if the tyres slip on the rims and there’s rolling resistance. On top of that is soil compaction and shortened tyre life.
TYRE PRESSURE MAKES THE DIFFERENCE
It’s a well-known fact that a tyre’s footprint, or rather ground contact surface area, is proportional to its pressure. In other words, the pressure in the tyre is almost equal to the pressure it exerts on the ground.
Pressure represents force per surface area. So, as the pressure in the tyre increases, the contact surface area decreases and the pressure on the ground increases.
The difference between the pressure in the tyre and the pressure on the ground is the result of tyre design – these two factors will converge as the flexibility of the tyre increases.
The logical conclusion to draw from this is that one’s tyres must always be at the lowest possible pressure, but with the proviso that tyres must do their work without being destroyed in the process.
A while ago we put a double wheel tractor with a heavy three-point ripper on the lands without checking the tyre pressure because they looked okay without a load.
Fortunately, the mechanic noticed that all was not well and did a spot-check of the sidewalls of the tyres. They were boiling hot due to fibres and wires rubbing against each other inside the tyre because the tyre was pushed beyond its design tolerance levels.
INCORRECT TYRE PRESSURE IS EXPENSIVE
Incorrect tyre pressure can be catastrophic. According to Firestone, tyre pressure that is a mere 10% below specification can shorten the lifespan of a tyre by 15%.
A tyre that gets as hot as described above, is likely to be more than 10% too flat, and the damage at say 20% below specification will be more than 30%. This doesn’t even take into account the possible damage to tyres which slip on the rim. This can destroy a tyre in no time at all.
On the other hand, pressure above specification has its own disadvantages: reduced operator comfort, increased wear and tear on hard surfaces because of the reduced contact area, increased fuel consumption and soil compaction.
HOW TO DETERMINE TYRE PRESSURE
The optimum pressure for your tyres is determined by the tyre design, the load on the tyre and the speed at which you work. As far as the design is concerned, it is essential that you research the tyre brand properly.
Michelin’s latest ultra-flexible tyres can, for example, operate on the land at a pressure as low as 80 kPa (0.8 bar) to increase their footprint by up to 37%.
If you have the right model, as well as the height and profile, you can check the optimum pressure on the manufacturer’s tables according to the tractor’s weight per axle as well as the desired working speed. Nowadays you can simply install an app on your phone that does it for you.
For example, with the Michelin Pressure Calculator app you specify the weight and quantity of tyres per axle and the details of the various tyres. The app can also do it for you if you scan the QR code on the tyres with your phone.
You must also specify the type of implement being used. Then you take a photo of the tractor in the app on which you must indicate the different axles, the tractor’s front end and implement’s centre point.
Using this information, the app calculates the optimal tyre pressure given your work speed. This takes away all the guessing.
WHAT ARE YOUR NEEDS?
What the tractor is used for will determine the tyre pressure.
“You cannot use the same pressure for planting, ploughing and roadwork,” says Mr Jakkie van Heerden from tyre manufacturer Trelleborg.
Trelleborg has developed a series of phone apps to help farmers to determine the correct pressure for tractors and implements.
The Trellerborg Tyre Efficiency app requires certain information: the tractor’s weight, the type of tyre, the type of implement that will be towed and the work that will be carried out.
The app then calculates the ideal tyre pressure.
Jakkie says the season will also influence the kind of tyre pressure needed. “At the beginning of the planting season, the farmer can check each tractor individually and adjust the tyre pressure. This may take a day, but the benefits for the farmer are worth it. The tractor’s optimal force can be placed on the soil, improving flotation and traction.”
TYRE PRESSURE FACTS FOR TRACTORS
* Uneven wear and tear, shortened tyre life, damage to the sidewalls and tyres that slip on the rim.
* 20% under pressure = 26% loss of performance.
* Increased soil compaction, increased wear and tear, reduced operator comfort, shortened tyre life and increased fuel consumption.