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Federal Register / Vol. 86, No. 169 / Friday, September 3, 2021 / Proposed Rules
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the tire manufacturers recommended cold inflation pressure.
The static loaded radius arc is easy to measure, but the imaginary line tangent to the static loaded radius arc is difficult to ascertain in the field. The approach and departure angles are the angles between the line tangent to the static loaded radius arc and the level ground on which the test vehicle rests. For the compliance test procedure, a substitute measurement will be used. A
measurement that provides a good approximation of the approach and departure angles involve using a line tangent to the outside diameter or perimeter of the tire and extends to the lowest contact point on the front or rear of the vehicle. This approach provides an angle slightly greater than the angle derived from the true static loaded radius arc. The approach also has the advantage to allow measurements to be made quickly for measuring angles in the field to verify data submitted by the manufacturers used to determine light truck classification decisions. In order to comply, the vehicle measurement must be equal to or greater than the required measurements to be considered as compliant and if not, the reported value will require an investigation which could lead to the manufacturers vehicle becoming reclassified as a passenger car.
3 Running Clearance NHTSA regulations define running clearance as the distance from the surface on which an automobile is standing to the lowest point on the automobile, excluding unsprung weight. Unsprung weight includes the components e.g., suspension, wheels, axles, and other components directly connected to the wheels and axles that are connected and translate with the wheels. Sprung weight, on the other hand, includes all components fixed underneath the vehicle that translate with the vehicle body e.g., mufflers and subframes. To clarify these requirements, NHTSA previously issued a letter of interpretation stating that certain parts of a vehiclesuch as tire aero deflectors that are made of flexible plastic, bend without breaking, and return to their original positionwould not count against the 20-centimeter running clearance requirement. The agency explained that this does not mean a vehicle with less than 20
centimeters running clearance could be elevated by an upward force that bends the deflectors and still be considered compliant with the running clearance criterion, as it would be inconsistent with the conditions listed in the introductory paragraph of 49 CFR

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523.5b2. Further, NHTSA explained that without a flexible component installed, the vehicle must meet the 20centimeter running clearance requirement along its entire underside.
This 20-centimeter clearance is required for all sprung weight components. For its compliance test procedure, NHTSA
will include a list of the all the components under the vehicle considered as unsprung components.
NHTSA will update the list of unsprung components as the need arises.
4 Front and Rear Axle Clearance NHTSA regulations state that front and rear axle clearances of not less than 18 centimeters are another criterion that can be used for designating a vehicle as off-highway capable.496 The agency defines axle clearance as the vertical distance from the level surface on which an automobile is standing to the lowest point on the axle differential of the automobile.
The agency believes this definition may be outdated because of vehicle design changes, including axle system components and independent front and rear suspension components. In the past, traditional light trucks with and without 4WD systems had solid rear axles with center-mounted differential on the axle. For these trucks, the rear axle differential was closer to the ground than any other axle or suspension system component. This traditional axle design still exists today for some trucks with a solid chassis also known as body-on-frame configuration. Today, however, many SUVs and CUVs that qualify as light trucks are constructed with a unibody frame and have unsprung e.g., control arms, tie rods, ball joints, struts, shocks, etc. and sprung components e.g., the axle subframes connected together as a part of the axle assembly. These unsprung and sprung components are located under the axles, making them lower to the ground than the axles and the differential, and were not contemplated when NHTSA established the definition and the allowable clearance for axles. The definition also did not originally account for 2WD
vehicles with GVWRs greater than 6,000
pounds that had one axle without a differential, such as the model year 2018
Ford Expedition. Vehicles with axle components that are low enough to interfere with the vehicles ability to perform off-road would seem inconsistent with the regulations intent of ensuring off-highway capability.
In light of these issues, for the compliance test procedure, NHTSA will 496 49

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ask manufacturers to identify those axle components that are sprung or unsprung and provide sufficient justification as a part of the testing setup request forms sent to manufacturers before testing. In addition, for vehicles without a differential, NHTSA will request the location each manufacturer used to establish its axle clearance qualification.
NHTSA will validate the location specified by the manufacturer but will challenge any location on the vehicles axle found to be located at a lower elevation to the ground than the designed location of its axle clearance measurement.
5 49 CFR 571.3 MPV Definition The definition for multipurpose passenger vehicle MPV is defined as a a motor vehicle with motive power, except a low-speed vehicle or trailer, designed to carry 10 persons or less which is constructed either on a truck chassis or with special features for occasional off-road operation. 497 The regulation is silent, however, in defining special features for occasional off-road operation are qualified. In a letter of interpretation dated May 31, 1979, the agency responded to a question from Subaru requesting the agencys opinion whether a four-wheel drive hatchback sedan could be classified as an MPV.
NHTSA responded stating that the agency interprets the definition as requiring that the vehicle contain more than a single feature designed for offroad use and that four-wheel drive would be useful in snow on public streets, roads and highways, so this feature cannot be determinative of the vehicles classification if there are no features for off-road use. The interpretation also stated that Subaru needed to provide additional information including, but not limited to, pictures or drawings of the vehicle concerning other special features of the vehicle that would make it suitable for off-road operation. Finally, the interpretation referenced 49 CFR
523.5b2 for a description of some of the characteristics that would be considered special features for offroad operation although that section relates primarily related to fuel economy. Considering that the definition for MPVs does not list the special features, NHTSA is seeking comment on whether manufacturers use special features other than those in 49
CFR 523.5b2 to qualify vehicles as MPVs. Should NHTSA link the definition of MPV in 49 CFR 571.3 as it relates to special features for occasional off-road operation to 49 CFR
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