A load of difference

Making the right capacity calculations critical during installation

Article April 15, 2003
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The National Truck Equipment Association's Technical
Services Department regularly receives questions from members who have been
asked by their customers to install a body and/or equipment on a chassis, that
once installed, leaves the user insufficient payload capacity for the
anticipated function of the completed vehicle. The following discussion covers
how to calculate a vehicle's net payload, the first step in determining if a
chassis has adequate payload capacity for its intended function.

A truck must not only carry a payload, but also must
carry its own empty weight, passengers and the weight of the body and/or
equipment installed on it. Each truck has a gross vehicle weight rating (GVWR)
and a separate front and rear gross axle weight rating (GAWR). When fully
loaded the weight of the completed vehicle must not exceed the GVWR, and the
weight must be distributed so that the GAWR of each axle is not exceeded.

Be sure to check federal, state and local weight laws to
ensure that neither the government weight restrictions nor the GVWR and GAWRs
are exceeded for your application. The GAWR is determined by the lowest rated
capacity of the tires, brakes, wheels, suspension and axle assembly. The GVWR
is determined by the chassis and axle ratings.

In order to determine the maximum payload of a completed
vehicle, it is first necessary to know the GVWR. The GVWR may be determined by
using the GVWR Selector Chart in the model section of the truck data book. The
ratings also are contained in the incomplete vehicle document and on the
certification label.

Next determine the curb weight of the model and add to it
the weight of passengers, driver, body and/or equipment (Note: allow 150 lb per
occupant seating position with seat belt). Subtract this Total Vehicle Weight
from the GVWR to obtain the maximum allowable payload. The example below will
help illustrate.

Once the maximum net payload is determined, a weight
distribution calculation must be performed to ensure that the individual axle
loads do not exceed the GAWRs and governmental weight laws and restrictions.

To further assist you in calculating net payloads, the
NTEA has developed a Payload Analysis Worksheet. To order or if you have
questions, contact NTEA Business Development Director Doyle Sumrall at
330/283-2176; e-mail [email protected].

Calculation of Maximum Net Payload

Chassis-Cab GVWR
( 10,000 lb

Chassis Curb weight with
all options ( + 4,126 lb

8-ft utility body with rear bumper and front-mounted
winch ( + 1,200 lb

Completed Vehicle

Curb Weight = 5,326 lb

Driver and passengers - + 450 lb

Total Vehicle Weight

Including passengers - 5,776 lb

Maximum Net Payload

10,000 lb ( 5,776 lb = 4,224 lb

Payload Analysis Worksheets and FMVSS Compliance
Worksheets are available in pads of 100 ($4 for members, $8 for nonmembers). To
order, call 800/441-NTEA.

About the author: 
Kleinstiver is director of Technical Services for the National Truck Equipment Association, Farmington Hills, Mich.
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