Kiyoshi Narabu, General Manager
Technical Department
Ichikoh Industries, Ltd.
80 Itado, Isehara
Kanagawa, 259-11
Japan

Dear Mr. Narabu:

This is in reply to your letter of August 19, 1997, asking for an interpretation of Federal Motor Vehicle Safety Standard No. 108, specifically, S7.8.3 and S7.8.4.

The first sentence of S7.8.3 states that "When a headlamp system is tested in a laboratory, the range of its vertical aim shall not be less than +/-4 degrees from the nominal correct aim position for the intended vehicle application." To the same effect is the first sentence of S7.8.4 which prescribes a horizonal aim tolerance of +/-2.5 degrees. You state that "there are no provisions that prescribe the aim range formed out of [the] vertical and horizontal axis," and submit four Figures of various aim range possibilities and ask whether they conform to Standard No. 108.

Your Figure 1 represents a literal interpretation of S7.8.3 and S7.8.4, depicting vertical and horizontal aim tolerances. However, these are not meant to be mutually exclusive. At any point within the +/- 4degree vertical aim the horizontal aim must be adjustable +/- 2.5 degrees and vice versa, in order to ensure that headlamp aim is correct over the broadest possible range within both the vertical and horizontal directions. This means that Figure 1, as we interpret it, does not represent the correct interpretation of S7.8.3 and S7.8.4 when these paragraphs are read together.

Figure 4 represents our interpretation of Standard No. 108 describing the full rectangle of aiming possibilities created by the plus and minus aspects of the vertical and horizontal aim tolerances. Because Figures 2 and 3 with their "lozenge" and "ellipse" aiming areas respectively do not cover the full range of horizontal aim over the full vertical range of +/- 4 degrees they do not represent a correct interpretation of Standard No. 108.

I hope that this answers your questions.

Sincerely,
John Womack
Acting Chief Counsel

ref:108

d.9/11/97