This article was published in the August 2013 edition of NTEA
News
Question: We are a truck equipment distributor, and
we have noticed the term “unloaded vehicle weight” mentioned a number of times
in body builder books and, especially, in the incomplete vehicle documents. What
is so important about this weight?
Answer: Unloaded vehicle weight is a key
characteristic of a vehicle’s compliance to the Federal Motor Vehicle Safety
Standards (FMVSSs). It is utilized in a couple of different ways, as related to
these requirements, which is why it appears so many times in an incomplete
vehicle document (IVD). Unloaded vehicle weight is used by the National Highway
Traffic Safety Administration (NHTSA) as a threshold for the application of some
FMVSSs, and it is also used by chassis manufacturers as a limit for compliance
with a particular FMVSS.
NHTSA defines unloaded vehicle weight in Code of Federal Regulations
(CFR) 49 Part 571.3 as “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.”
This may sound like an elaborate definition of what the industry would
call “curb weight”. However, NHTSA actually defines curb weight in the same
section as unloaded vehicle weight. According to NHTSA, 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.”
For the most part, both terms are synonymous as they are used
throughout the FMVSS regulations in some of the test procedures. But unloaded
vehicle weight is additionally used as part of the application of different
FMVSS requirements, such as in FMVSS 208, which states in S4.2.6.2, “Trucks,
buses, and multipurpose passenger vehicles with a GVWR of 8,500 pounds or less
and an unloaded vehicle weight of 5,500 pounds or less
manufactured on or after September 1, 1998….”[emphasis added],
where vehicles with an unloaded vehicle weight above 5,500 lbs. would be
excluded from this particular requirement.
You may also recognize the term as one of the ingredients in the value
for which manufacturers must account in their assignment of the gross vehicle
weight rating for a new motor vehicle on the certification label from CFR 49
Part 567.5(d)(2)(iii):
“'Gross Vehicle Weight Rating' or 'GVWR' followed by the appropriate
value in kilograms and (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."
Since weight so heavily influences the outcome of dynamic testing,
unloaded vehicle weight is referenced greatly in the FMVSSs that involve such
tests applicable primarily to vehicles with a GVWR of 10,000 lbs. or less. From
the chassis OEM perspective, unloaded vehicle weight is one of the
characteristics of a vehicle as it goes through its FMVSS compliance testing and
development. Since more mass means more crash energy that has to be managed for
something like a frontal barrier test, the heaviest unloaded vehicle weight a
manufacturer uses to successfully pass these tests becomes the “maximum unloaded
vehicle weight” that the OEM will represent as one of the means for achieving
pass-through compliance. By keeping the curb weight of the vehicles you complete
at or under the maximum, you preserve traceability back to the successful test
results of the OEM. Building vehicles heavier than this value goes outside of
what the OEM is representing based on its testing, so you would need to rely on
some other method of compliance besides the conformity statements in
the
IVD.
Conversely, you may see a reference to a “minimum unloaded vehicle
weight” in an IVD. These would typically apply to compliance with brake system
requirements, where a vehicle that was completed with a weight below the minimum
specified in the IVD potentially could have issues meeting requirements
involving
anti-lock brake system functions for a particular
chassis.
Notes referencing the importance of meeting these weight limitations
can be found in the IVDs (see examples in the sidebar at
right). Building vehicles within the limits, minimum or maximum, for
unloaded vehicle weight is probably the most important element of complying with
the FMVSS that apply to vehicles with a GVWR of 10,000 lbs. or less.
If you have any questions on lighting or other vehicle compliance
questions, contact the NTEA Technical Services Department at 1-800-441-6832,
Monday–Friday from 8:00am–5:00pm. We’ll be happy
to help!