Interpretation ID: 77-1.33

TYPE: INTERPRETATION-NHTSA

DATE: 02/25/77

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: Harley Murray, Inc.

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 25, 1977, question whether a row of eight wheels arranged in a line that is perpendicular to the longitudinal axis of a vehicle constitute an "axle" as that word is used in S3(b) of Standard No. 121, Air Brake Systems. You note that the wheels are not mounted on a single solid axle but rather are mounted on two walking beam assemblies that also constitute the suspensions for a separate set of eight wheels across the vehicle.

The answer to your question is yes. When asked for a definition of "axle system" in connection with Standard No. 121, the National Highway Traffic Safety Administration stated:

In answer to Wagner's request for a definition of "axle system," the term is used in the same sense as it is used in the definition of GAWR found at 49 CFR 571.3. "Axle system" is used instead of "axle" to avoid confusion in situations where a suspension system does not employ an axle. The term has not created difficulty in the GAWR definition (39 FR 17553, May 17, 1974).

The agency's use of "axle" in S3 is intended to be identical to its use of the phrase "axle system." Thus, "axle" means the arrangement of wheels that lie across the vehicle in a line that is perpendicular to the longitudinal centerline of the vehicle. This understanding of "axle" and "axle system" is used regularly in the assignment of gross axle weight ratings (GAWR) on vehicles that employ independent suspensions in place of solid axles.

From your description, it appears that each row of eight wheels on your trailer constitutes an "axle" or "axle system" that could be rated at a GAWR in excess of 29,000 pounds, qualifying the vehicle for exclusion from Standard No. 121.

SINCERELY,

HARLEY MURRAY, INC.

January 25, 1977

Duane A. Perrin, P.P. Handling & Stability Division

SUBJECT: Application of exemption 121 S3 (b) to Murray 16 tire trailer

Thanks for the copy of "Standard 121" which we discussed over the phone on December 29th.

I am requesting your confirmation that our 16 tire expandable trailer comes under the exemption provided for any vehicle with "(b) An axle that has a gross axle weight rating (GAWR) of 29,000 pounds or more."

Our 16 tire trailer has two rows of eight wheels each. For purposes of permit loading these rows of wheels are designated as axle number 4 and 5 on the State of California Department of Transportation permit form (copy enclosed). My question is this: Do the rows of eight wheels constitute an "axle", as provided for in exemption (b) quoted above? They are not mounted on one solid axle, but are mounted in a walking beam assembly (see picture marked exhibit B).

In California, the allowable permit load on this trailer axle grouping is 58,400 pounds when the trailer is expanded to 10 feet. That is a maximum of 29,200 pounds for axle number 4 and 29,200 for axle 5 using the California permit definition of axle.

We are using Rockwell-Standard axles with a capacity rating of 20,000 pounds for four wheels or 40,000 pounds for each row (axle?) of eight wheels. That's a total rated capacity of 20,000 pounds for the 16 wheel axle grouping.(two rows).

I hope you will agree that the exemption (b) does indeed apply to our 16 tire trailer and that each row of eight wheels constitutes an axle in the federal law 121, as it does in the State of California permit form. If this is the case, we do not need to persue a petition for exemption. If, on the otherhand, wording of the Standard 121 does not exempt our 16 tire trailer we will petition for a modification due to the very tight fit of the brake/ axle/ walking beam assembly on this trailer, which is required to meet height limitations when loaded with heavy oversized equipment as shown in some of the enclosed photos.

Thank you for your attention to this matter. If I can clarify this situation or answer any questions please give me a call at (209) 466-6639.

Dave Murray