Interpretation ID: nht72-2.39

DATE: 06/13/72

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

TO: Lox Equipment Company

TITLE: FMVSS INTERPRETATION

TEXT: This is in reply to your letter of May 17, 1972, concerning problems you are having establishing gross axle weight ratings on vehicles you manufacture. You indicate that the problem occurs because brake drums which you use do not come with manufacturer's ratings, but are merely recommended for use with certain axles. You also ask whether a motor vehicle safety standard will require a 40-foot stopping distance from 20 mph.

Your understanding that brake drum capability does not have to be considered in determining gross axle weight rating is not entirely correct. The gross axle weight rating, which is the load carrying capacity of a single axle system (49 CFR 571.3), is a measure of the safe load-carrying capacity of the entire axle system. Manufacturers should include components in their vehicles that are designed to handle loads up to these ratings. Normally an assembler can rely on the specifications or the advice of a reputable supplier as to the capacity of the supplier's components. We expect manufacturers to exercise due care in ensuring that purchased components are adequate and safe for the vehicles they are used on, in accordance with careful business practices. These do not necessarily have to take the form of formal "ratings."

With reference to your question regarding stopping distance, Standard No. 121, Air Brake Systems, effective September 1, 1974 (not July 1, 1972) will, among other things, require a vehicle to stop from 20 mph in 33 and 54 feet on surfaces with skid numbers of 75 and 30 respectively.