OECD AGR/CA/T(2000)35 Narrow tractor definition

At the 2002 OECD Annual Meeting an Italian proposal was put forward for solving the applicability of Code 6 when narrow tractors exceed the minimum track width of 1150 mm. The proposal was rejected because of opposition by the French Delegation. In the Engineer's Conference in Madrid we would like to submit a new proposal, directly derived from the previous one, clearer in some points and still responding to the aim of extending the field of application of OECD Codes 6 and 7 to tyre types widely used on narrow-track tractors and manufactured for matching the tractors to normal operating conditions for these tractors. Narrow-track tractors The narrow-track agricultural tractor has been defined in the field of application of OECD Codes 6 and 7. The field of application of these Standards does not allow narrow-track tractors to be fitted with tyres set at a minimum track width wider than 1150 mm, enabling, however, tyres to be fitted with adjustable track width which, sti11 having a minimum track width of not more than 1150 mm, can be set at higher track widths during normal operation of the tractor. There is an apparent inconsistency in the field of application. In fact the Standard allows the tractor track width to be adjusted, because in field use of the tractor there must be the need to exceed the width of 1150 mm. The only compulsory point is that the minimum track width has to be less than 1150 mm. The type of protective structure allowed for the narrow-track tractor, when it is mounted in front of the driver's seat and is the dual-pillar type to be folded down if necessary, has been studied working in field conditions where space around the tractor is often limited. This is necessary for working requirements but is also recognised as being less effective than the other types of protective structure (frame, cab, rear non-folding roll-bar). It is thus necessary to verify not just the strength of the structure itsel f but also the tractor behaviour in the most severe preparation for lateral stability and, because the dual-pillar structure is considered unable to protect the driver during a continuous roll-over of the tractor if it overturns laterally on a slope, in the same tractor preparation, it must also be tested if the protective structure is designed to prevent continuous rolling over. Tests carried out at the Department of Agricultural Economics and Engineering of the University of Bologna showed that tyres, known as terra-tyre, which can be fitted on a narrow­ track tractor and always determine a tractor track width wider than 1150 mm have the same behaviour as the tyre types currently allowed in the field of application of OECD Code 6, when set at the allowed maximum track widths. The two preliminary tests, on lateral stability and non-continuous behaviour, foreseen by Code 6 are normally evaluated separately during the OECD tractor tests but they are part of a single test procedure. These two tests are two well-defined stages that must be satisfactorily completed in the preparation foreseen by the Standard. The static lateral stability of the tractor must first be verified, in a tractor configuration which, in the trial conducted in Bologna, was shown to be the most stringent for the group of tractors analysed; then the non-continuous rolling test must be performed. In the trial this test did not give positive results in the tractor preparations that represented the best conditions in terms of lateral stability. These results, apparently contradictory, appear logical if the two tests are considered strictly linked together. First of all the tractor lateral stability is verified in the worst tractor preparation for this aspect, and then, only if the angle of inclination is at least 3