Tractor Tyres - How to Choose the Right Pressure

If you have a tractor then its maintenance would be your first priority- isn’t it?

Apart from checking the fuel tank, inspecting battery condition, sharpening blade attachment, and checking belts for cracking, what you need to keep an eye on during every maintenance period are the tractor tyres. Weight being hauled by the tractor, and the inflation pressure are the two most important factors that can cause deformation in tractor tyres.

Tyre pressure is vital to making the tractor work at its best. It's not as simple as it sounds, because it's really tough to adjust the accurate pressure to maintain their longevity.

Here’s why it's a significant factor in tractor maintenance!

What is tyre pressure important for a tractor?

The biggest challenge faced by the agro-industry is probably balancing out the pressure when varied loads are placed on the tyres of the tractors while driving them on different surfaces. The right adjustment can help reduce wear, thereby allowing them to last longer.

Moreover, rolling your tractor on the road at the wrong pressure affects its performance, which may in turn lead to severe financial impact. Inaccurate tyre pressure can even reduce power efficiency up to 20%-30% through tyre slip and rolling resistance.

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How to figure out that your tractor tyre pressure isn’t correct?

There are a few basic points that can act as an indicator of tyre pressure.

• Tyre footprint is one of them- it is the area of the tyre in contact with the ground. This depends upon the air pressure within the tyre. Tyre inflation pressure is pretty similar to ground pressure exerted by the tyre, though not identical.

Tyre pressure ∝ 1/ Tyre footprint

This means the more the tyre pressure the smaller the footprint.

So, when you see a larger tyre footprint it indicates greater traction, less wheel slip, less fuel use, longer tyre life, greater output, and less soil compaction. And, the scenario is just the opposite when you see smaller footprints. Hence, we may assume that keeping tyre pressure low is the main target.

As per the recent trends, large tyres are capable of running at low ground pressure for cultivation and drilling work. Hence, the pressure of the tractor tyre should be kept at 0.8 bars or below for efficient productivity. Whereas, the optimum tyre pressure for trucks is between 8 bar and 9 bar.

• Tyre Size is another factor that helps to strive for optimum tyre pressure. To understand the tyre size theory it's vital to understand the terminologies related to it.

Take an example of a John Deere tractor tyre- 520/85R42 158 A8 R1

• Load is also a major indicator of whether your tractor is running at the correct tyre pressure. Let’s discuss how!

Let’s assume, for a particular pressure at a certain rate of speed the load is 3150kg. If the pressure gets doubled at the same rate of speed, the load will be around 4400kg. While with the increased pressure if speed is increased 4-times the load becomes 3400kg. Therefore, the pressure change influences the load capacity more than what speed change does. Hence, if the pressure goes up or down the recommended level though there won’t be any visible consequences, there would be a 15% reduction in the life expectancy of the tyre.

• Over-inflation of tyres results in an increased knock-on effect, poor operator comfort, reduced tyre life and increased fuel consumption. However, under-inflated tyres or low tyre pressure may cause more severe damage than over-inflation. Under-inflation causes unbalanced wear, sidewall damage, bead slip and increased fuel use.

A standard tyre has a proper balance between load per tyre in kg, speed in km/h and air pressure, which is also known as three-way relationship.

Finding the right pressure is difficult in some situations. Here’s how you can deal with the right tyre pressure!

1. Parameters that control tyre pressure: Tyre technology, tyre design and components define how much weight your tyre can carry. Several parameters that help improve the efficiency of your vehicle by adjusting the tyre pressure are:
   • Pressure based on load and speed
   • Optimal slip ration
   • Weight on each of your machine’s axles
   • Forward speed
2. The volume of air: No matter what, the air contained in the tyre is proportional to the load carried. Without the correct quantity of air in each tyre, they cannot properly carry the weight on each tractor axle. Even when you ballast your tyres with water, it causes a nearly 25% drop in air volume in the tyres, thereby resulting in major variation in inflation pressure. Therefore, do keep a check on the air volume in each of your tractor tyres to maintain the right tyre pressure.
3. Steps to increase the load that your tractor tyre can carry:
   • Increase pressure by introducing more compressible air to support a heavier load.
   • A greater volume of air in the tyre helps in increasing the machine's load capacity.
   • Tyre size equivalent to SRI can also help in increasing load capacity.
   • Another option is choosing a new VF tyre generation with NRO option that allows higher load benefit without hanging the rim.
4. Ways to calculate tyre pressure:
   • Manual calculation: The main logic is to find the load on each axle, both on the front and rear.

     Front Load=(M1×(d1+E))/E+Front axle weight

     Rear Load= (M2×(d2+E))/E+Rear axle weight

     Read manufacturer details to get the front axle and rear axle weight.
     M1- front ballast weight
     M2-weight of the rear-mounted tool
     d1- distance between the center-point of the front ballast weight and center of the front axle.
     d2- distance between the center of the rear axle and the center-point of the rear-mounted tool.
     E- distance between the center of the front axle and the center of the rear axle.

   • Use weighing equipment for correct weight distribution: To find the actual weight supported by each axle keep weighing equipment. Then distribute the weight on each axle to get the exact load on each tyre. Optimizing the pressure yields less wear on the powertrain components & tyres, less soil compaction, more productivity and better fuel consumption.
     Note: The right way to distribute weight is 60% rear and 40% front with or without implementation.
5. Ways to enhance the tyre pressure control: Exact tyre pressure optimizes comfort and limits soil compaction, which makes it easy to work on fields. Low pressure for the field is suitable while higher pressure is needed for tractors to roll on the road. This is so because it increases the tractor's stability by reducing the rolling resistance, fuel consumption and wear to the tyres. But what’s ideal for mixed use, both on road and field. There are two ways to comply recommended pressure value:
   • CTIS: Central Tyre Inflation System, which is meant to control and adjust in real time. This is the most effective solution for mixed use.
   • TMPS: Tyre Monitoring Pressure System helps in controlling the pressure in real time and alerts you when you are far from recommended pressure value.

Conclusion

Tyre pressure is an inevitable part in enhancing the longevity of tractor tyres. Proper adjustment can ensure longer life with improved productivity. This two word terminology is self-explanatory but comes with a lot of technicalities. Keep a check on it for the smooth operation of your tractors and balance out other parameters related to it for better efficiency.