How OEMs determine gross vehicle weight rating

From an NTEA member 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? 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 pounds 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 pounds 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 pounds (3,500 kg.) GVWR or less — 135: Light Vehicle Brake Systems Vehicles greater than 7,716 pounds (3,500 kg.) GVWR — 105: Hydraulic and Electric Brake Systems Vehicles 8,500 pounds (3,855 kg.) GVWR or less — 225: Child Restraint Anchorage Systems Vehicles 10,000 pounds (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 pounds 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 pounds, rear GAWR = 21,000 pounds, GVWR = 25,999 pounds). 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 pounds (0–2,722 kg.) Class 2 — This class of truck has a GVWR of 6,001–10,000 pounds (2,722–4,536 kg.) Class 3 — This class of truck has a GVWR of 10,001–14,000 pounds (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 pounds (6,351–7,257 kg.) Class 5 — This class of truck has a GVWR of 16,001–19,500 pounds (7,258–8,845 kg.) Class 6 — This class of truck has a GVWR of 19,501–26,000 pounds (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 pounds (11,794–14,969 kg.) Class 8 — This class of truck has a GVWR of greater than 33,001 pounds (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

How OEMs determine gross vehicle weight rating

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