Interpretation ID: nht74-2.27

DATE: 06/12/74

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Truck Trailer Manufacturers Association

TITLE: FMVSS INTERPRETATION

TEXT: This is in response to your letter of May 29, 1974, concerning paragraph S5.3.2 of Federal Motor Vehicle Safety Standard No. 121, Air brake systems.

When a full trailer is tested for compliance with S5.3.2, the wheels on the steerable axle(s) cannot lock up at speeds above 10 mph except for controlled lockup of wheels allowed by an antilock system.

Yours truly,

ATTACH.

Truck Trailer Manufacturers Association

May 29, 1974

Larry Schneider -- Chief Counsel, National Highway Traffic Safety Administration

Subject: FMVSS-121 - Request for Interpretation

Dear Mr. Schneider:

A number of our members are currently involved in the redesign of braking systems in order to comply with the regulations specified by FMVSS.121. In this regard, we would appreciate your advice on the following:

Section S5.3.2 specifies antiwheel lockup control on all wheels except "lockup of wheels on non-steerable axles other than the two rearmost non-liftable, non-steerable axles on a trailer with more than two non-steerable axles."

Does this imply that all steerable axles must have antilock control?

Sincerely yours,

Burt Weller -- Engineering Manager