The importance of maximum unloaded vehicle weight in certification

In the commercial vehicle industry, gross vehicle weight rating (GVWR) is a well-known term. In vehicle application and operation, GVWR is widely understood as a value representing the maximum overall weight of a vehicle, including cargo, occupants, fuel(s), and fluids. Often less familiar but no less critical is the term unloaded vehicle weight (UVW), which describes the weight of the completed vehicle when empty. More formally, the National Highway Traffic Safety Administration (NHTSA) defines it in Title 49 Part 571.3 of the Code of Federal Regulations (CFR) as: “Unloaded vehicle weight means the weight of a vehicle with maximum capacity of 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.”Some may think that this simply describes a vehicle’s curb weight. While similar, NHTSA has a distinct definition for curb weight, also in Part 571.3 Definitions: “Curb weight means the weight of a motor vehicle with standard equipment; maximum capacity of engine fuel, oil, and coolant; and, if so equipped, air conditioning and additional weight optional engine.” In the case of a chassis completed with a rear body, as installed by a second stage upfitter, the weight of the body is included in curb weight.Why UVW is importantThough defined separately by NHTSA, UVW and curb weight are in fact not just similar, but functionally the same. However, UVW becomes important to upfitters when specified as a maximum (or minimum) value for a completed vehicle by an OEM. An OEM’s described maximum UVW is used to define the heaviest vehicle curb weight when completed for compliance with several Federal and Canadian Motor Vehicle Safety Standards (F/CMVSS) that can be affected by weight. When considering a chassis for upfit, it’s critical to first confirm that the comprehensive weight of the upfit items, when added to the chassis’ designated curb weight, will not exceed the maximum specified UVW. In the case of an OEM factory-completed pickup eligible for box removal, the weight of the original pickup box is subtracted from the curb weight, then the weight of the installed rear body is added, again, with any added equipment, to calculate a new curb weight.Since weight so significantly influences the outcome of dynamic testing, unloaded vehicle weight is referenced greatly in the F/CMVSS that involve tests primarily applicable to vehicles with a GVWR of 10,000 pounds or less.As such, and in order for an upfitter to utilize and benefit from pass-through compliance through an OEM’s dynamic testing, the maximum UVW is perhaps the most important element of complying with these safety standards. For upfitters, this might include standards like FMVSS 571.301: Fuel System Integrity, which applies to “passenger cars, and to multipurpose passenger vehicles, trucks and buses that have a GVWR of 10,000 pounds or less and use fuel with a boiling point above 32°F.”UVW is referenced in this standard as follows, with weight conversions added: “S7.1.6 The vehicle, including test devices and instrumentation, is loaded as follows: …(b) Except as specified in S7.1.1, a multipurpose passenger vehicle, truck, or bus with a GVWR of 4,536 kg (10,000 pounds) or less is loaded to its unloaded vehicle weight, plus the necessary test dummies as specified in S6, plus 136 kg (300 pounds) or its rated cargo and luggage capacity weight, whichever is less, secured in the load carrying area and distributed as nearly as possible in proportion to its GAWR. For the purpose of this standard, unloaded vehicle weight does not include the weight of work-performing accessories.”FMVSS 571.108: Lamps, Reflective Devices, and Associated Equipment, also utilizes UVW, describing the weight of a vehicle in a range from a UVW minimum up to the GVWR maximum for headlight aiming adjustment. Also note that while an FMVSS may not explicitly mention UVW in its regulatory language, it may still be used by a manufacturer to describe conditions for conformance. For example, in order to comply with FMVSS 126 - Electronic stability control systems for light vehicles, an OEM could specify a maximum UVW for a completed vehicle. This is why it’s important to consult IVDs and body builder information.UVW is also referenced in federal regulations outside of FMVSS, such as Title 49 of the Code of Federal Regulations Part 535: Medium- and Heavy-Duty Vehicle Fuel Efficiency Program. More broadly, UVW appears in Part 567: Certification, which affects all manufacturers of multi-stage vehicles. In this last case, CFR 567.4 Requirements for Manufacturers of Motor Vehicles, describes how GVWR is based upon UVW with added cargo and passenger loads, specifically stating: “‘Gross Vehicle Weight Rating’ or ‘GVWR’ followed by the appropriate value in pounds, which shall not be less than the sum of the unloaded vehicle weight, rated cargo load, and 150 pounds times the number of the vehicle’s designated seating positions. However, for school buses the minimum occupant weight allowance shall be 120 pounds per passenger and 150 pounds for the driver.”How to find a vehicle’s max UVWChassis OEMs publish their maximum UVW values in their incomplete vehicle documents (usually shipped with a chassis-cab/incomplete vehicle) or in their body builder book or upfitter guide (usually available online at the OEM technical support site). OEM body builder books and/or specification materials may include additional weight information necessary to perform weight analyses. Find body builder resources using the NTEA Chassis Manufacturer Directory at ntea.com/oemdirectory.Visit ntea.com/technicalresources for details on NTEA’s technical and engineering offerings.

The importance of maximum unloaded vehicle weight in certification

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