The scope of this SAE Recommended Practice, trailer axle alignment, is to identify the dimensional limits of, and a method to, establish a perpendicular relationship between the king pin centerline and the axle centerline at its midpoint. Various types of equipment are commercially available which can be used for this measurement which provides varying degrees of accuracy, but none can be endorsed by SAE.

The most fundamental methods of measurement will be described here, but other equipment is available if a greater degree of accuracy is desired.

This SAE Recommended Practice establishes the recommended locations for the air brake and electrical connections for towing multiple trailers. It applies to all commercial trailers except drop frame and car haul types.

This SAE Recommended Practice applies to highway trailer tow bar eye-type applications, including multiple trailers.

The information in this SAE Information Report is the result of studies by the Automobile Manufacturers Association, American Trucking Association, and Truck Trailer Manufacturers Association, to achieve interchangeability of equipment which will comply with the legal dimensional limitations for the majority of states and yet permit increased loading space within these dimensions. This in no way supersedes other information in the SAE Handbook on this subject.

Some cases will require more care in application allowing splash shield clearance at trailer support interference points and positioning fifth wheel to allow trailer swing clearance on an 11% grade. All dimensions are given in inches.

Table 1 and Figures 1 and 2 show basic requirements for interchangeability of truck tractor and semitrailer equipment. Figure 3 shows the interchangeability of the doubles converter dolly.

The formulas for determining LWC, OAL and CFW are:

where:

= fifth wheel advance

= Rear axle tire radius

= 90 in

= 64 in (short trailers specifically intended for use with two axle tractors)

= 96 in

= 102 in

= Clearance, 4 in

where:

= Distance from intersection at back of cab and trailer swing radius to top of fifth wheel with zero trailer clearance to first obstruction

= Top face of fifth wheel to centerline of pivot, 3.50 in

= Swing radius of trailer corner

This SAE Recommended Practice establishes the recommended locations for the air brake and electrical connections for the back of a truck-tractor and the front of a truck-trailer.

This SAE Standard applies to upper coupler kingpins for commercial trailers and semitrailers in the unladen condition. See Figure 1. A 90 degree ± 1 degree angle extends (in all directions) from the centerline of the kingpin to the upper coupler plate surface within a 48.26 cm (19 inch) radius. The upper coupler plate surface should not bow downward (convex) more than 0.635 cm (1/4 inch) within a 48.26 cm (19 inch) radius or more than 0.3175 cm (1/8 inch) at a radius of 25.4 cm (10 inches) from the kingpin. The upper coupler plate surface should not bow upward (concave) more than 0.15875 cm (1/16 inch) within a 48.26 cm (19 inch) radius. (See Figure 2.)

This SAE Recommended Practice covers the number, location, and method of attachment of safety chains for full trailers and/or converter dollies.

This SAE Recommended Practice applies to rigid bumper or rigid structure points and flexible components of passenger cars, multipurpose passenger vehicles, and light trucks. This document is intended as a guide toward standard practice and is subject to change to keep pace with experience and technical advances.