This article was published in the September 2013 edition of NTEA
News
Question: We’re a truck equipment distributor and
have noticed that on medium- and heavy-duty trucks, the gross vehicle weight
rating (GVWR) is normally equal to the sum of the axle ratings. However, for
lighter duty trucks, the GVWR is less than the sum of the gross axle weight
ratings (GAWRs). Can you explain why?
Answer: For light-duty trucks, the GVWR is
pre-determined from the specific selected axle/suspension, wheel/tire
combination, wheelbase, frame, frame reinforcements, etc. Light-duty frames are
complex designs that maximize the strength and rigidity of the vehicle while
minimizing the weight of the complete frame assembly. Frames are formed to
achieve a lower vehicle profile, and some frame assemblies incorporate
multi-piece designs, with variable depth sections that allow the manufacturer to
provide additional strength, where required. The light-duty chassis may have to
comply with up to 17 additional Federal Motor Vehicle Safety Standard
(FMVSS)/Canadian Motor Vehicle Safety Standard (CMVSS) 571 requirements that can
complicate the determination of the chassis GVWR.
Light- and
Medium-Duty Trucks
Light- and medium-duty trucks
(Classes 1–5, 19,500 lbs. GVWR and below) are similar to medium- and heavy-duty
trucks in so much as the manufacturers determine the front GAWR and rear GAWR
using the lowest rated components, like tires, suspensions, axles, etc. With
most light-duty chassis configurations, the GVWR is less than the sum of the
front and rear axle ratings. For many light-duty truck chassis manufacturers,
testing to the various FMVSS/CMVSS, ride and handling, and other vehicle
dynamics will help determine the proper GVWR to assign the chassis. Available
larger front and rear GAWRs provide the upfitter with the latitude in
accommodating the installation of various body styles and equipment, like
snowplows, aerial devices, liftgates, etc., and satisfying load requirements,
while staying below the manufacturer’s stated GVWR.
Manufacturers of light-duty trucks with GVWRs of 10,000 lbs. or less
must also comply with additional FMVSSs. Light truck manufacturers test
and validate the total vehicle as a complete system as well as provide
model-specific restrictions with which the upfitter must comply for braking,
fuel system integrity, lateral stability, occupant safety protection, and
vehicle dynamics, ride and handling.
Following are additional FMVSS/CMVSS requirements (depending on GVWR)
which lighter duty vehicles must meet:
- Vehicles 7,716 lbs. (3,500 kg.)
GVWR or less — 135: Light Vehicle Brake Systems
- Vehicles greater than 7,716
lbs. (3,500 kg.) GVWR — 105: Hydraulic and Electric Brake
Systems
- Vehicles 8,500 lbs. (3,855 kg.)
GVWR or less — 225: Child Restraint Anchorage Systems
- Vehicles 10,000 lbs. (4,536
kg.) GVWR or less — 110: Tire Selection and Rims; 114: Theft
Protection and Rollaway Prevention; 118: Power Operated Window Systems; 126:
Electronic Stability Control Systems; 138: Tire Pressure Monitoring System; 201:
Occupant Protection in Interior Impact; 202: Head Restraints; 203: Impact
Protection for the Driver from the Steering Control System; 204: Steering
Control Rearward Displacement; 213: Child Restraint Systems; 214: Side Impact
Protection; 216: Roof
Crush Resistance; 219: Windshield Zone Intrusion;
and 301: Fuel System Integrity.
Medium- and
Heavy-Duty Trucks
Determining the GVWR for medium-
and heavy-duty trucks (Classes 6–8, GVWR 19,501 lbs. and greater) is a rather
simple and straightforward process. The truck manufacturers provide a wide range
of GAWR and GVWR offerings to satisfy a specific customer’s vocation,
applications and duty cycle requirements. Manufacturers and their truck
component suppliers design, assign and provide capacity ratings for each of
their respective components. From these component ratings, the truck
manufacturers determine and report both the front and rear GAWRs. The GAWR
defaults to the lowest rated components used in the combination for the complete
front and rear axle. The sum of the front and rear GAWRs determines the
truck’s GVWR.
Medium- and heavy-duty truck manufacturers provide a variety of models
that can be tailored to meet a customer’s needs. Each model will
have a wide range of axles, suspensions, brakes and tire/wheel capacities to
match required GAWRs and GVWR. In addition to those offerings, the customer can
select from numerous available wheelbases that include choices of frame material
and frame reinforcements. The truck can be customized to meet the customer’s
application, vocational need and payload requirements, while still complying
with federal, state and local weight and size regulations.
Again, there are always exceptions. Some truck chassis
manufacturers allow the dealer and customer to order front and rear
axle systems where the combined sum exceeds the GVWR. This allows for specifying
heavier rated capacity axle system components that will have the higher GAWRs
for durability and commonality for service parts, while the truck has a lower
rated GVWR. (Example: front GAWR = 9,000 lbs., rear GAWR = 21,000 lbs., GVWR =
25,999 lbs.).
If you have any questions about this article or any other
technical or engineering-related topic, call the NTEA
Technical Services Department at 1-800-441-6832 from
8:00am–5:00pm (EST), Monday-Friday. We’ll
be happy to help!
DEFINITIONS
GVWR (Gross Vehicle Weight Rating)
The truck possesses components that are adequate to safely carry the
maximum total weight, measured at the tire-ground interfaces. This is a
manufacturer’s rating for the vehicle, the maximum amount that a loaded truck
should weigh, including the weights of the truck chassis, body, occupants and
cargo. The GVWR is controlled by the component sizes and ratings. Included in
these component factors are frame strength, axle, suspension, brakes, wheel
capacities and tire capacities. It’s common for trucks of the same model or
series to have a range of GVWRs. The capacities of suspension components account
for such differences. The manufacturer’s GVWR may be equal to or less than, but
cannot exceed, the total of the front and rear gross axle weight
ratings.
GAWR (Gross Axle Weight Rating)
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
GAWR is determined by the weakest component, such as suspension, axle, tire,
wheel and brakes.
The following are generally accepted truck classifications by the work
truck industry for classes and GVWRs. Class is determined by the vehicle’s
GVWR.
Light-Duty Trucks (Classes 1, 2 and
3)
- Class 1 — This class of truck
has a GVWR of 0–6,000 lbs. (0–2,722 kg.)
- Class 2 — This class of truck
has a GVWR of 6,001–10,000 lbs. (2,722–4,536 kg.)
- Class 3 — This class of truck
has a GVWR of 10,001–14,000 lbs. (4,536–6,350 kg.)
Medium-Duty Trucks (Classes 4, 5 and 6)
- Class 4 — This class of truck
has a GVWR of 14,001–16,000 lbs. (6,351–7,257 kg.)
- Class 5 — This class of truck
has a GVWR of 16,001–19,500 lbs. (7,258–8,845 kg.)
- Class 6 — This class of truck
has a GVWR of 19,501–26,000 lbs. (8,846–11,793 kg.)
Heavy-Duty Trucks (Classes 7 and
8)
A Class B commercial driver’s license is required to operate these
vehicles.
- Class 7 — This class of truck
has a GVWR of 26,001–33,000 lbs. (11,794–14,969 kg.)
- Class 8 — This class of truck
has a GVWR of greater than 33,001 lbs. (14,969 kg.), and includes all
tractor-trailers
EXAMPLE
Medium-Duty Single Axle Truck
Tires: 265/75R22.5G
Single rated capacity — 5,205 lbs. each x 2 = 10,410 lbs.
Dual rated capacity — 4,805 lbs. each x 4 = 19,220 lbs.
Wheels: 22.5 x 7.50, 10-hole disc wheel
Rated capacity — 6,610 lbs. cap. at 120 lbs.
maximum inflation pressure
Service Brakes: Air drum
Front — 15 x 4 with 20” chambers, 11,000 lb.
maximum rated capacity
Rear — 16.5 x 7 with 30” chambers, 26,440 maximum rated capacity
Axles:
Front — 11,000 lbs.
Rear — 17, 850 lbs.
Suspensions:
Front — 12,000-lb. capacity taper leaf
springs
Rear — 19,000-lb. capacity air ride
Frames and Frame Reinforcements: 175” WB with 80,000 PSI with inverted
“L” reinforcement
Front — 10,000 lbs. capacity without
reinforcement/13,220 lbs. capacity with
reinforcement
Front GAWR Components: The frame is the lowest rated component at
10,000 lbs.
Tires — 10,410 lbs.
Wheels — 6,610 lbs. x 2 = 13,320 lbs.
Brakes — 11,000 lbs.
Suspension — 12,000 lbs.
Frame — 10,000 lbs.
Rear GAWR Components: The axle and suspension are the lowest rated
components at 19,000 lbs.
Tires — 19,220 lbs.
Wheels — 26,440 lbs.
Brakes — 26,440 lbs.
Axle — 19,000 lbs.
Suspension — 19,000 lbs.
Front GAWR 10,000 lbs. + Rear GAWR 19,000 lbs. = 29,000 lbs.
GVWR