The effect of tyre size on the non-continuous rolling test for narrow tractors

In both the OECD Code and the EC Directive for testing dual-pillar front-mounted roll-over protection structures for narrow track width tractors, a non-continuous rolling preliminary test in case of lateral overturning is provided. This test can be simulated with a computer programme. The role of the tyres (and also of the rims) in the lateral overturning of narrow tractors is very important. Frequently the same tractor can be alternatively equipped with four, five, or more different tyre combinations, which can vary its total mass, width, centre of gravity position and moment of inertia about its longitudinal axis. According to the Standards the preliminary test must be carried out with the tractor fitted with tyres having the greatest diameter. Tests carried out on 17 tractors and 50 tyre combinations show that in eight of the 17 cases examined, the tyres providing the most restrictive conditions were not the highest ones. Therefore, the Standards do not provide the most restrictive conditions for the preliminary test of non-continuous rolling. This paper supports the selection of the tyres giving the highest moment of inertia of the left (or right) wheels about the tractor longitudinal axis for the non-continuous rolling test. Using this parameter in 14 of the 17 cases, the most restrictive conditions are met. (C) 2001 Silsoe Research Institute.