Adjusting Tire Pressure to Prevent Soil Compaction
The weight of a tractor acts on the soil through the tires. There are two ways to reduce its impact: increase the wheel diameter to fit wide, high-volume tires to distribute the weight, or decrease the tire pressure. The real challenge is to find the right balance between the pressure needed for transport and work. Tire pressure is a crucial factor for productivity, yield, soil health, tire longevity, and fuel consumption.
Soil compaction
Compaction, or soil compaction, results from natural phenomena (heavy rains) and passes of agricultural machinery. It is one of the primary factors limiting yield by affecting the overall functioning of the soil: it reduces soil aeration, water infiltration, soil exploitation by the root system, penalizes earthworm fauna…
This compaction can occur at three levels: surface, in the first ten centimeters, deep, from 20 cm down, and between the two, the plow pan.
Surface compaction
Surface compaction is less damaging than deep compaction. It is caused by underinflated tires, overly worked soil, and too many machinery passes.
Plow pan
The plow pan is generally present in clay soils. It is caused by the frequent passage of the plow at the same depth, poor maintenance of the plow, especially the sharpening of the shares.
Deep compaction
Deep compaction is the most damaging, especially on yield, and it can last about ten years. It is primarily caused by the weight of tools on wet soil.
Underinflation
Reducing tire pressure preserves the soil and increases productivity. However, excessive underinflation can prematurely wear tires if they are not designed to operate at low pressure.
Tire structure wear
Excessive underinflation can prematurely damage the tire structure, causing:
- Abnormal wear of the lugs (tire treads) and shoulders (transition between the tread and the tire sidewall).
- Heating of the tire structure materials.
- Separation of the rubber and carcass components.
Solutions to avoid wear due to underinflation
- Road : Slightly increase pressure above normal, especially under load, to reduce ground resistance and heating.
- Fields : Use tires at optimal pressure (refer to manufacturer data).
Overinflation
An overinflated tire, regardless of load, compacts the soil. Slippage, often due to overinflation, increases fuel consumption by more than 20%. Excessive slippage (over 15%) causes horizontal sliding of the top soil layers, risking soil structure degradation.
Solutions for overinflation
Low-pressure tires can be used. Agricultural low-pressure tires (VF, Very high Flexion) are an effective solution to reduce soil compaction. This technology increases resistance, flexibility, load capacity and traction. Their reinforced structure allows them to support heavy loads, up to 40% more than standard tires, without damaging the soil, while maintaining a lower pressure, generally around 0.8 bar, whereas standard agricultural tires cannot go below 1.2 bar.
Calculating the weight on each axle
Weighing tool
To calculate the weight supported by each axle, a weighing device can be used. Simply divide the obtained weight by two and define the optimal pressure for each axle group. For weighing the front axle, the rear tool must be placed on the ground. For weighing the rear axle, the rear tool must be lifted (to account for road linkages). Without weighing equipment, a manual calculation can be done.
Manual calculation
Data
It is possible, without weighing equipment, to manually calculate the load on each axle with:
- The empty weight of the agricultural machine: from manufacturer information (front axle weight, rear axle weight).
- The weight of front ballast: M1
- The weight of the rear mounted tool: M2
- The distance between the center of the front axle and the middle of the front ballast weight: D1
- The distance between the middle of the rear mounted tool and the rear axle tool: D2
- The distance between the middle of the rear axle and the front axle: E
Formulas
- Front load : [ M1 x (D1+E) ] / E + front axle weight
- Rear load : [ M2 x (D2+E) ] / E + rear axle weight
Applications
Several applications allow determining the ideal pressure. The main tire manufacturers (Bridgestone, Continental, Michelin, Nokian tyres, Trelleborg, and Vredestein) have joined forces to offer a common solution to farmers: the app Agro Tyre Pressure. This app compiles the databases of all manufacturers (pressure, load, and speed charts) and allows, after entering load, speed, brand, and tire size, quick and easy access to the correct inflation pressures. Other manufacturers have also created their tools such as: Michelin, Bridgestone, Firestone…
Recommendations
Recommended pressures depending on the type of work[1]:
- Road : Increase pressure to reduce rolling resistance. On the road, pressure is higher for safety, improving stability and braking.
- Fields : Decrease pressure to increase traction and reduce slippage. Low pressure increases vibration damping, reducing fatigue and lower back pain.
- Plowing and heavy work : Decrease pressure to increase traction, reduce slippage, save fuel, reduce tire and equipment wear, and decrease work effort.
It is recommended to inflate/deflate according to loads and type of work. There are tire inflation systems that continuously adjust tire pressure.
Pressure according to use
It is important to adapt tire pressure according to use: on road or in fields.
- On road : Underinflation accelerates premature tread wear. Overinflation can cause accidents at high speed. For road use, add an extra 0.4 bar to limit premature tread wear on asphalt, which is more abrasive than soil.
- In fields : Overinflation promotes rut formation, soil compaction, and reduced root development of crops.
Pressure according to the tool
It is important to know the load per axle and consult manufacturer charts to determine the appropriate pressure.
It is necessary to measure the actual weight supported by each axle, as information on the distance between the tractor axle and the tool can be approximate.
Constantly adapt pressure
Tire pressure must vary according to load, outside temperature, wear, and type of use. It is important to check it regularly.
Adjusting pressure daily allows to reduce wear and extend tire life by more than one year, reduce fuel consumption by 20% per year, and avoid soil compaction.
- TPMS : The Tire Pressure Measurement System is an electronic monitoring device for tire pressure. This system consists of sensors on the tires and a control monitor integrated into the cabin to inform the driver in real time when the pressure of one or more tires is inappropriate.
- Complete tire inflation system : This device is installed directly on agricultural tires. It adjusts pressure during use, directly from the cabin. There are several scenarios for installing a tire inflation system.
- The tractor is pre-equipped to receive this device: it already has pneumatic braking, so the installation will be simpler and cheaper. In this case, the original air compressor may be underpowered to simultaneously inflate all 4 wheels within a limited time, so inflation will just take a bit longer.
- The tractor is not pre-equipped: A complete installation including a compressor and rotary joints must be planned, which ensure air passage between the fixed axle and the rotating wheel.
- Without device, it is necessary to check pressure regularly to inflate or deflate tires manually.
- Software TASC (Tool to calibrate tires, developed by Agroscope, Swiss agronomic research institute): The tool calculates the optimal inflation pressure based on soil and machine data to limit soil compaction and rut formation. TASC takes into account texture (tactile examination), surface bearing capacity (screwdriver test), maximum loosening depth, tire width and diameter, wheel load, and inflation pressure. The tool has a database of over 1,000 agricultural and forestry tires and allows comparing their soil impact, rim compatibility, and maximum authorized load.
Observing the impact on soil
Terranimo is a OAD, developed by Danish (Aarhus University) and Swiss (Agroscope) research teams, which evaluates the impact of work on soil compaction considering wheel load, inflation pressure, clay content, and suction force.
The output provides the stress exerted on the soil, soil resistance, and risk of compaction in the top 35 cm of soil.
Investments and costs
TPMS
The average cost is €400 including 4 sensors (which fit directly in place of the valve in the tires), a 12V-24V display, a 12V-24V cable with power plug, a mount, and installation manual.
Tire inflation system
This device consists of an electronic control module (OCP), a compressor (present on tractors with pneumatic braking), rotary joints (ensure air passage between the rotating wheel and fixed axle), and a monitor for display.
- Upfront consideration : The installation time and price depend on the number of axles to equip and, in the case of a trailer, whether the axles are pre-drilled or not. It is therefore preferable to plan tire inflation when choosing the trailer: pre-drilling axles and choosing tires! The benefit of tire inflation is lost if the trailer wheels are too small and cannot lower pressure.
- Cost : The price of a tire inflation system starts at €3,800 for equipping a tractor with a braking compressor. Prices go up to €20,000 for a tractor/trailer set (including installation).
- Benefit : This system offers time savings, fuel savings, increased yield by reducing compaction, reduced maintenance (less wear), and improved comfort.
Alternative to reduce ground pressure
Besides pressure, it is also possible to act on the force application surface. Tracks or dual wheels, due to their large contact area with the soil, reduce the stress exerted on the soil.
Sources
12 simple tips to better manage agricultural tire pressure, tractor tire expert, 2020, Bridgestone
11 keys to know everything about agricultural tire pressure, 2023, Bridgestone
7 essential points to manage my tractor tire pressure, 2021, Firestone
Tools to help pressure adjustment, 2018, Reussir
A tool to calibrate tires, 2014, Perspectives agricoles
