New artic code
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• The Institute of Road Transport Engineers has issued a new code on the coupling of articulated vehides. It goes further than either the British Standard or the International Standard but caters for interchange between all three.
The IRTE code states the dimensions and formulas needed to provide for an interchange between old and new trailers with front overhangs between one and 1.6m, and allows trailers to couple to both two and three-aided tractive units.
The range of coupling heights is restricted to 1,220 to 1,340mm, but with recommended target heights of 1,320 or 1,240mm.
For predictions of load distribution, maximum kingpin loads of 10 tonnes for two-axled tractive units and 14 tonnes for three-aided tractive units are recommended.
Many semi-trailers operating in the UK have shorter front overhangs and more length behind the coupling than their Continental counterparts so that there is a real risk of exceeding the 15.5m overall length limit.
British operation often encounters steeper dips and humps than is assumed in the ISO standard, so the IRTE code allows for nine degrees of vertical articulation fore and aft in the straight-ahead position and eight degrees where the tractive unit comes closest to the front-end swing of the trailer.
To keep coupling heights low, manufacturers are recommended to limit rear suspension bump clearance to 180nun. Graphs in the code allow compatibility of equipment to be assessed easily and the method of calculating weight distribution is explained to prevent axle overloading.
The code Coupling Artics is available from the IRTE at 1 Cromwell Place, London SW7 2JF at 25 per copy.