Interpretation ID: nht89-1.44

TYPE: INTERPRETATION-NHTSA

DATE: 03/20/89

FROM: ERIKA Z. JONES -- CHIEF COUNSEL NHTSA

TO: CONRAD S. BROOKS -- ENGINEERING MANAGER FISHER ENGINEERING

TITLE: NONE

ATTACHMT: LETTER DATED 12/01/88 FROM CONRAD S. BROOKS TO ERIKA Z. JONES -- NHTSA, OCC 2859

TEXT: Dear Mr. Brooks:

This responds to your December 1, 1988, letter concerning the applicability of Federal regulations to motor vehicles to which a detachable snowplow is attached. I will respond to each one of your specific questions below.

Question One: "Please confirm in writing that the substructure for a snowplow mounting that is permanently attached to a four wheel drive vehicle may be attached to and be forward of the front bumper without violating any existing or proposed vehicle saf ety standard."

Response: We cannot make such a blanket statement. The weight and the location of the substructure might affect the vehicle's compliance with Standard No. 105, Hydraulic Brake Systems (49 CFR @ 571.105) and Standard No. 120, Tire Selection and Rims for Motor Vehicles Other Than Passenger Cars (49 CFR @ 571.120). Any person attaching such a substructure before the first retail sale of the vehicle would have to certify that the vehicle with the substructure attached complied with all applicable safety s tandards. Any commercial business attaching such a substructure after the first retail sale of the vehicle must ensure that the addition of the substructure does not "render inoperative" the vehicle's compliance with any safety standard. Commercial bus inesses are prohibited from "rendering inoperative" a vehicle's compliance with any safety standard by section 108(a)(2)(A) of the National Traffic and Motor Vehicle Safety Act (15 U.S.C. 1397(a)(2)(A)).

Question Two: "Is the snowplow blade, being detachable and used only a few hours each year, considered as part of the vehicle payload when it is attached?"

Response: None of our regulations define or otherwise mention the term "vehicle payload." We assume that you are referring to calculation of the vehicle's weight when you speak of its "payload." If this is the case, we have definitions of many different weight calculations set forth

in 49 CFR @ 571.3 and in our individual safety standards. Some of these weight calculations would exclude a detachable snowplow blade. For instance, "unloaded vehicle weight" is defined in 49 CFR @ 571.3 as:

the weight of a vehicle with maximum capacity for all fluids necessary for operation of the vehicle, but without cargo, occupants, or accessories that are ordinarily removed from the vehicle when they are not in use. (emphasis added).

In a January 18, 1977, letter to Mr. D. J. Henry, the agency stated that portions of a snowplow that would ordinarily be removed from the vehicle when they are not in use (such as a snowplow blade) would not be included in calculating the "unloaded vehic le weight."

If you would identify the particular weight calculation in which you are interested, we would be pleased to tell you whether the weight of a detachable snowplow blade should be included in that particular weight calculation.

Question Three: "Does this exempt a vehicle, with the blade attached and raised, from having to meet the Front Gross Axle Weight Rating restrictions?"

Response: No. There are no exemptions from the gross axle weight ratings. 49 CFR @ 571.3 defines gross axle weight rating as "the value specified by the vehicle manufacturer as the load carrying capacity of a single axle system, as measured at the tire -ground interfaces." The vehicle manufacturer or any vehicle alterer must base its certification of the vehicle's compliance with all applicable safety standards on the assigned gross axle weight ratings.

NHTSA answered the specific question of how detachable snowplow blades are considered in determining whether a vehicle is within its assigned gross axle weight ratings in a March 8, 1976, letter to Mr. Edward Green. In that letter, we stated that any de termination of whether a vehicle was within its assigned gross axle weight rating would include the weight imposed on that axle system by a snowplow with the blade attached and raised.

Question Four: Is there a specific limitation of what percent of the vehicle curb weight can be supported by the front axle? The Ford Truck and Body Builders Layout book specifies a maximum of 63 percent for the front axle.

Response: None of our regulations, including the definitions of "gross axle weight rating" and "gross vehicle weight rating," specify any weight distribution limitations or proportions for the front axle of a vehicle. The only issue for the purposes of our safety standards is whether the vehicle complies with all applicable standards when it is loaded to its assigned gross axle weight ratings. As long as the vehicle complies with our standards under those loading conditions, it makes no difference wha t proportion of the curb weight is assigned to each axle.

We assume the reason that Ford's guidebook specifies a maximum of 63 percent of the vehicle's curb weight to be supported by the front axle is to ensure that the proportional load stopped by the vehicle's front and rear brakes will be such that the vehic le can be certified as complying with our braking standard. Any commercial entity that modified a Ford vehicle in such a way that more than 63 percent of the curb weight were supported by the front axle would have to certify that the modified vehicle com plied with our braking standard, if the modification were made before the first retail sale of the vehicle, or make an initial finding that the modifications did not result in "rendering inoperative" the vehicle's compliance with our braking standard, if the modifications were made after the first retail sale of the vehicle.

Question Five: If the portion of curb weight on the front axle is only dictated by vehicle performance, can NHTSA suggest a source for some general guidelines to avoid performance testing?

Response: As noted in response to Question Four, vehicle performance is the only limitation on the proportion of curb weight that can be assigned to the front axle. For vehicles that are modified before the first retail purchase, the entity making the m odifications can consult the instructions provided by the incomplete vehicle manufacturer. An example of these instructions is the Ford Truck and Body Builders Layout book to which you referred in your letter. Those instructions generally establish som e limits on the parameters of the completed vehicle, such as its weight, height of center of gravity, and so forth. When the entity modifying the vehicle completes the vehicle within the limits established by the incomplete vehicle manufacturer, the mod ifier is not required to conduct its own testing or engineering analyses.

When a vehicle is modified after its first retail purchase, the modifier could remain within the gross axle weight ratings and gross vehicle weight ratings labeled on the vehicle. If the modifier does so, it would not need to conduct any testing or engi neering analyses.

If you have any further questions or need more information on this subject, please feel free to contact Marvin Shaw of my staff at this address or by telephone at (202) 366-2992.

Sincerely,