Tires: technicality and innovation at the service of agriculture

Suitable criteria for choice and optimum management of inflation pressure not only ensure a better performance of tires from the point of view of techniques, mechanics and economy but also substantially reduce their impact from the agricultural point of view. The industry puts on the market an extremely wide range of tires for all work requirements

According to statistics made public by ETRMA, the European Tyre and Rubber Manufacturers' Association, more than seven million tires for use in agriculture were sold in Europe in 2013 alone. In Italy in this year the market was estimated to 400,000 tires with only one-quarter of this number from the European Union countries and the majority imported from such countries as India, China and Turkey. The remarkable growth of these products of Eastern origins is due mainly to increasing competition in this market but the improvement in their quality reported in recent years is not to be underestimated.

Statistics show that there is still confidence in tires manufactured within the European Union, especially when the search is for high performance.

As it is, the tire is a very important and sensitive component for tractors and other agricultural machinery and must guarantee ideal performance from various points of view along with great load and traction capabilities, low resistance in transit, low levels of slippage and compaction of the ground during driving in various operational conditions and, last but not least, long life.

 

Criteria for choice of tire

 

There are two basic categories of tires: conventional and radial. Conventional tires are made with nylon threads layered at a biased angle which, while the tire rotates, are subjected to great tension which can result in energy losses. Radials, now strongly preferred for agricultural use, have a carcass of cords of polyester, steel or other  materials inlaid radially with several layers of rubber to confer a greater deflection angle under load resulting in less sensibility to shocks on the sidewall and greater stability on steep road gradients. Moreover, size being equal, radials feature better ground contact which corresponds to lower tire pressure and thus less soil compaction.

Other than structure, the profile of the tire is highly important for its performance. There are five main tire profiles on the market: three types for agriculture, R1, R1W, R2; two for grass cover, R3, and transport, R4.

R1 type treads are the most suitable for ordinary use on various types of terrain and in various conditions of humidity. The R1Ws are similar to the R1 but with a profile height generally 20% greater designed for tractors working in conditions which are especially humid but also for ensuring good performance in transport.

The R2 type profile has a high central groove or rib, the areas between the treads, even doubled, and more inclined that that of the R1 to guarantee good traction and continuous cleaning of the tread during operations in muddy conditions, as in rice paddies. This profile is not suitable for conventional full-field operations because of the lack of traction provided and the risk of breaking the central groove if the tire is subjected to high torsion. On the R3 profile, the grooves account for 70% of the tire's external surface to provide ideal distribution of the load on the ground. The R3 type is suitable for use on trailers as well as machinery for groundskeeping. The grooves on the R4 profile are generally 30% lower compared to the R1 and take up 50% of the external surface. These tires are largely used on industrial machinery for earthmoving thanks to their excellent traction on paving and adequate performance on unpaved ground.

 

What the market is offering

 

There is actually an extremely wide variety of tires on the market. An example is that the Terlleborg catalogue alone offers 140 models of tires for drive wheels for agricultural tractors. An analysis of the solutions proposed on the market by the leading manufacturers – Alliance, Avon, Bridgestone, Bandenmarkt, Bkt, Continental, Dunlop, De Molen, Firestone, Fulda, Good year, Kleber, BKT, Michelin, Mitas, Nokian, Pirelli, Trelleborg, Taurus and Vredestein – shows that 75% of their tires have rim diameters of 20 to 38 inches and widths which vary from 260 to 710 mm.

The width plays a fundamental role in many operational features. Other than reducing soil compaction, greater width means not only a high load capacity (see the graph below) but also positive interaction on the tractor's traction performance.

 

Greater agronomic safeguarding

 

Increasing traction, reducing fuel consumption and improving comfort in driving have been only a few of the main objectives in the evolution of tires.

Coming to the fore in recent years, however, has been reducing the effects of soil compaction becoming much more a reality compared to the recent past. The reason for this interest can be easily explained by the increase in machinery mass in relation to work capacity which uniformly cuts across all agricultural machinery capabilities, from medium-high power tractor categories to harvesting machinery. 

This means that working directly on the reducing mass, the most feasible solution, is limited, at least from the technical point of view, so there is the possibility of increasing the surface of the driving components coming into contact with the ground and working on the properties of the tires and the management of inflation pressure.

Thus the direction in the evolution of tires is towards solutions for a low relationship of shape and highly flexible shoulders making it possible to increase the contact surface over that of conventional tires to work to the advantage of traction and reduced compaction.

Other than the technical-construction properties, an important role is taken on by pressure; high pressure can, in fact, sharply reduce the tread area in contact with the ground. The reduction of pressure, a feature of radial tires, makes it possible to optimize traction abilities by reducing slippage while reducing compaction through the greater distribution of weight on the surface coming into the contact with the terrain. But it must also be considered that reducing tire pressure can carry the negative effect of higher fuel consumption and greater wear due to elevated resistance in transit encountered especially in road transport.

Allowing greater inflation pressure for transport and reducing pressure for work operations has become possible through the application of automatic tire pressure control operated directly from the driver's seat. These systems bring together a compressor, a series of valves and an integrated rotating distributor at the heart of systems becoming increasingly widespread on tractors, trailers and harvesting machinery, systems providing optimum management of tire parameters according to the conditions in which they are operating (Tab. 1). 

 

 

Within reach of an APP

Within the past few years the number of apps for use in farming has multiplied, applications which work on tablets or smartphones for facilitating the collection and transmission of data.

There is no shortage of apps of interest also for tires. There were already three apps in operation in 2011 –  the Trelleborg Loan Calculator, the Firestone Tire Pressure Calculator and the more recent Goodyear Tire Manager – which, according to the app, make it possible to estimate optimum pressure for tire inflation for configuration of the machine for the distribution of the load. Testifying to the usefulness of two of the apps are the thousands of people who have already downloaded them to their smartphones. 

Also of interest is the possibility of monitoring pressure in real time by linking the smartphone of a tire pressuring monitoring sensor (TPMS) mounted on the tire valve. With an app such as the Steelmate TPMS, the GoSafe TPMS or iTPMS, anomalies in tire pressure variations caused by a puncture or a shift in the load, for example, are recognized and signaled by the sensor.

Among the many apps developed for the automotive sector are those, for example, for recognition and conversion of tire codes, the Tire Calculator, Tire Facts, or Car Tires PRO for calculating replacement tire size and apps adapted for agriculture use are certain to come along in the near future. And finally there are many measuring instruments to be used for the efficient management of tires such as the Partometer camera measurement of area, the Angle Meter to determine inclination and the Vibration Meter and Sound Meter Pro for gauging vibrations and sound level.

This is a strongly evolving field, one which is certain to facilitate the gathering of information for optimizing the performance of these crucial components of agricultural tractors.