MANAGEMENT OF TRACTOR TIRE AND BALLAST

In tractor operation, tractive efficiency measures how well a tractor can use the power available at the axle to pull any implement attached to it through the soil. Improving of the tractive efficiency reduces the costs through improved fuel efficiency and increases the productivity of the used tractor. To enhance and improving tractive efficiency does not necessarily require a purchase in new equipment. The time spent in improving tractive efficiency provides immediate fuel savings and improved performance of the machine.

In tractor operation, the best approach to maximizing the tractor performance and minimizing compaction is to first select an equipment set that is best suited to the tractor that will pull it. Each piece of equipment should be sized so that the tractor can delivers maximum power to the soil at speeds of four to five miles per hour. If a tractor is used for either primary and secondary tillage or light-duty work such like planting, the primary tillage implements should then be relatively narrow and the light-duty implements should be wider so that each implement requires similar total draft forces when pulled at appropriate speeds during operation.

Operational tractive efficiency

The tractive efficiency is the fraction of power available at the axle that is actually delivered to an implement through the aid of the drawbar. Power is transmitted most efficiently to surfaces that do not deform under pressure and where the traction is great enough to prevent the wheels from slipping during operation. The tractive efficiency on soils is limited both by the rolling resistance and by the wheel slip. Maximum power is available at the peak of each of the curves in where the tractor parameters are commonly optimized to allow 8-15 percent slip. The power is then limited by excessive rolling resistance on the left side of the curves and by the excessive wheel slip on the right side of the curves. Maximum tractive efficiency of the tractor results from a compromise between minimizing rolling resistance and minimizing the slippery nature of wheel.

The modern day tractors are designed in such a way to transmit large amounts of power to the soil. Transmitting that power of the tractor requires a very large frictional forces, or traction, at the soil surface. Traction can be increased by the increasing of either weight or contact area. Weight added to it creates greater force at the soil surface, which also cause greater soil compaction and increased soil strength. The increased soil strength resists the forces applied by a tire as it transmits power to the implements in contact with the soil, but the additional weight cause a deeper track, which increases the rolling resistance.

Compaction of soil

Compaction of soil is an increase in bulk density which is also a decrease in pore space of the soil that is often caused by applying pressure to the soil with tractors and other heavy equipment such as trucks, combines and grain carts. Compaction of the soil can lead to a physical barrier to normal healthy root growth, causing the symptoms of water stress as well as nutrient stress. The effects of reduced pore space are reduced water infiltration, soil water holding capacity, and exchange of air.

In the period when moisture is either in short supply or excessive, the pore space in a well-structured soil then acts as a reservoir and conduit system for the water, then buffering the effects of moisture extremes. An ideal soil consists of about 50 percent pore space which is allocated equally to air and water. Pore space in the soil also allows for the roots to displace soil as they grow. But heavy wheel traffic, especially under wet soil conditions, damages soil structure and packs soil particles closely together, then reducing the soil pore spaces. A tightly packed soil is a serious condition for plants. 

Plant roots encounter physical barrier to growth due to the fact that there is nowhere to move the soil, and the reservoir and conduit system for air and water is shut down. Any practice that minimizes soil pressure also minimizes the soil compaction. Maximizing tractive efficiency and minimizing compaction are often compatible results and both increase profitability in the operation.

Management of power

Tractor drive trains are not designed in a way that they can provide maximum power in lower gears. Maximum power which is delivered at low speeds requires large forces that can cause premature wear on drive trains. Maximum power which is delivered at a higher speed requires smaller soil forces as well as smaller traction requirements. Implements with large draft requirements, such as primary tillage tools, should be sized so that they can be operated at minimum speeds of at least four or five miles per hour. Pulling an implement at higher speeds reduces both drive train wear and soil compaction when the tractor is ballasted properly. The combination of smaller implements pulled at higher speeds reduces the weight needed to achieve maximum tractive efficiency and this also minimizes the pressure which is applied to the soil surface and reduces compaction of the soil.

Management of ballast

The management of ballast should be to achieve just enough traction to transmit power to the ground without slippery of excessive wheel. Most of the power is always lost to wheel slip. Excess ballast causes a deeper track that increases rolling resistance. Power is lost from an over-ballasted tractor because the wheel must climb out of the deeper track that it creates. Optimum ballast is a compromise between wheel slip and rolling resistance.

Tilled or soft soils require more ballast for traction. Tillage reduces the strength of the soil, which then increases the depth of tracks and reduces traction. More power is lost to both rolling resistance and wheel slip on tilled or soft soils than on no-till or firm soils. Ballast should be distributed between the front and rear of the tractor in the correct proportions to then achieve maximum tractive efficiency as well as stability. The location of the drawbar on a tractor causes weight transfer from the front axle to the rear axle when the tractor is pulling an implement. Weight transfer is especially evident on a two-wheel-drive tractor when the front end and due to this reason, the steering becomes so light difficult.