Specifies the requirements for the location of fifth wheels and kingpins on vehicles used in dedicated combinations operating normally on both sealed and unsealed roads.

This Standard specifies requirements for the location of fifth wheels and kingpins on vehicles used in dedicated combinations operating normally on both sealed and unsealed roads. These requirements are applicable to prime movers, semitrailers, and multi-trailer combinations.The individual vehicles which make up a dedicated combination are only intended to be used within that dedicated combination or within a family of identical dedicated combinations. Therefore, many of the interchangeability requirements are expressed in relative terms, rather than absolute terms.For example, the height of the fifth wheel on the prime mover would be required to be within a certain tolerance of the height of fifth wheels on other prime movers within the same family. If semitrailers in a multi-trailer combination are to be interchanged the heights of the fifth wheels on the prime mover and on the leading semitrailer would also be required to be within a certain tolerance of each other. What the actual height is does not matter, it is the relative heights which determine interchangeability.By contrast, the absolute requirements for non-dedicated combinations require the height of all fifth wheels to lie within a certain dimensioned range.This Standard gives guidelines on interchangeability for coupling of the prime mover and semitrailers to provide compatibility and adequate clearance. However, this will not guarantee that any particular vehicle combination will satisfy legal requirements such as load distribution or overall length. Other aspects such as dynamic stability are not addressed.NOTES:1 Specific dimensional recommendations are given where applicable in this Standard to minimize interchangeability problems between conventional prime movers and semitrailers of a dedicated combinations. Such wider interchangeability is recommended wherever possible and may be of vital importance in an emergency.2 This Standard makes provision for coupling of any semitrailer of a multi-trailer combination to the prime mover.

First published as part of AS D17-1970.Revised and redesignated AS 2174-1978.Revised and redesignated in part as AS 2174.2-1994.Second edition 2006.Reconfirmed 2016. Originated as part of AS D17-1970. Previous edition AS 2174.2-1994. Second edition 2006.