How to choose the ideal tire

Agricultural mechanization in Brazil experienced great growth after the Second World War, due to some government incentives in relation to the country's industrialization and mainly due to the purchase of machinery from American and European markets. We must also add the competence of our rural producers. However, all these imported technological innovations were not adapted to the Brazilian reality. According to Mundo Agrícola magazine in 1965, the implementation of the national tractor industry only began in the same year as the creation of the Working Group on Mechanization in Agriculture, through which studies began to adapt these imports to our needs.

During this period of adaptation, Brazil suffered a great shortage of basic food products and this fact was the result of the high demand for food in large urban centers, linked to low production in the countryside, which was caused by the lack of good technological resources. and little technical support for increasing yields in agricultural crops. From then on, the need to expand the agricultural sector in the country arose, and then it was during the military regime that advances in agricultural frontiers began, mainly towards the Brazilian Cerrado, together with the expansion of the number of crops cultivated internally, which throughout the time were improved and adapted to the reality of the tropical climate and soil.

Over the last 20 years, the panorama of the Brazilian agricultural market (agronomic, forestry and livestock sectors) has been shaped in accordance with globalization and, in opposition to the former strong participation of the state in the market, companies have been strengthening themselves and providing the coordinates in agribusiness current. With these countless innovations and solutions, producers need knowledge to decide what is best for their needs, always taking into account the cost-benefit ratio, of course.

As agricultural frontiers develop and expand, there has been an increasing movement of machines and equipment for soil management and planting/sowing crops, as well as an increase in the power and weight of the tractors used. This increasing traffic of machines in cultivated areas has caused significant changes in the soil, mainly with regard to compaction, resulting in difficulties for root growth, decreased porosity, permeability and availability of water and nutrients for plants. It also results in an increase in nitrogen losses, increased costs for soil preparation and increased erosion due to reduced water infiltration.

Among the specifications of the tractor to be used, the farmer must also pay attention to the type of tire, as this is the element responsible for contact with the soil and for traction between the tractor and equipment. Traditionally, since the post-war period, with imports and government incentives for industrial development, so-called conventional or diagonal tires have been used on Brazilian agricultural machines, which are characterized mainly by having a carcass made up of plies that overlap one another. others, forming an angle of 45^o relative to the axis of rotation of the wheel. However, the opening of the economy to a greater volume of imports, starting in 1994, allowed the entry of the radial agricultural tire, which has stood out to this day. The radial tire is already known in the market, both agricultural and forestry, and differs from the diagonal tire by having a 90° ply angle.^o relative to the axis of rotation. Due to the recent arrival of this type of tire on the domestic market, we demand more studies on its functioning and performance compared to conventional tires.

A study carried out by the Agroforestry Machines and Tires Testing Center (Nempa), located at the Faculty of Agricultural Sciences of the Universidade Estadual Paulista (FCA/Unesp), in Botucatu (SP), evaluated the contact area between the tire and a support surface standard, comparing a conventional (diagonal) tire with a radial tire. The contact area was evaluated as a function of the vertical load (represents the weight of the tractor and implement applied to the tire) and the pressure used to inflate it.

Two agricultural tires with similar dimensions and equivalent uses were used in the work, one with a diagonal construction, model 23.1-30, tread width of 540mm and the other with a radial casing, model 620/75 R30 and tread width 547mm. To simulate the application of load on the tires, a vertical hydraulic press was used, driven by a hydraulic system and electronically controlled via computer. Both tires were tested with internal pressures of: 110,3; 124,1 and 137,9kPa (16, 18, and 20psi), at six different vertical loads, being: 20,2; 21,6; 22,6; 23,8; 25,1 and 26,5kN, loads predetermined depending on the application of tires on agricultural tractors.

The tires were fixed to the axis of the hydraulic press and, using a load cell to measure the vertical force, the loads were applied to the tires on a flat metal surface. Cardboard paper was used between the tire and the metal surface, on which the tire claws were “printed” and thus allowed the determination of the contact area. The entire system was controlled by a computer using a program for control and automation of electromechanical equipment. At the lateral ends (edges) of the claws printed on the cardboard, parallel straight lines were drawn forming a rectangle, making it possible to delimit the area hit by the tire. Photos were then taken with a digital camera, which were used in the image processing program “ImageJ”, which is an easy-to-use software designed to measure areas of digitized figures.

Based on the dimensions of the rectangle used as a reference, the program calculated the tire's contact area using the shape of a digital ellipse, which represents the shape of the tire resting on the surface. It should be noted that only the tire claws were marked on the cardboards, however, considering the application on agricultural soils (mainly tilled soils), the representation of the total contact area can be considered as the area of ​​the claw and between the claws ( Ellipse). The data obtained from the measurements carried out were organized in an electronic spreadsheet and the observations of the contact areas were compared between the different treatments.

In the graphs, it can be seen that the radial tire presented curves with higher contact area values, therefore, it generates a better distribution of the load (or mass) over a given surface, including agricultural soils. With this behavior, the radial tire can be more efficient in the field, both in reducing soil compaction, traction efficiency and saving in fuel consumption. Although the radial construction tire presents some benefits that have been proven, it has a higher acquisition cost and, therefore, its advancement in the field does not reach greater proportions. It is important to take the necessary precautions recommended by the manufacturer, such as inflation pressure according to the load and application of the tires, maximum tolerable ballast, mounting the wheel in a clean and safe place, among other precautions specific to each manufacturer.

This article was published in issue 141 of Cultivar Máquinas magazine. Click here to read the edition.