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Why Gross Vehicle Ratings Matter

Or, How Much Truck Do I Really Need?

When President Dwight D. Eisenhower signed the Federal Highway Act of 1956, he authorized building the Interstate Highway and Defense System, and initiated regulations for state and federal truck classes. Gross vehicle weight rating (GVWR) is the maximum weight of the vehicle, including body, occupants, fuel and cargo.

The standards are as follows:
• Class 1 (up to 6,000 lbs.)
• Class 2 (6,001 – 10,000 lbs.)
• Class 3 (10,001 – 14,000 lbs.)
• Class 4 (14,001 – 16,000 lbs.)
• Class 5 (16,001 – 19,500 lbs.)
• Class 6 (19,501 – 26,000 lbs.)
• Class 7 (26,001 to 33,000 lbs.)
• Class 8 (33,001 lbs. and above).

The classifications, originally aimed at governing size/weight limits and designating access of trucks and buses on the interstate system, are used by state and federal departments and regulators.

What Affects GVWR?

Components such as the frame system, transmission, drivetrain, suspension, brake system and tire load rating all have dramatic effects on GVWR. For example, an automatic transmission equipped with a park pawl (the park position on the gear indicator) can limit the GVWR. You alter the GVWR if you delete a cross member, change the load range of your tires or change springs.

While they may not affect the GVWR, other factors such as transmission and rear axle gearing can affect gradeability and driveability. Brakes are matched to the unit’s GVWR, but using inferior replacement brake pads or shoes can have a dangerous effect on stopping ability. Selection of replacement parts matters more than you think, but that’s another article.

Purchasing the Right Truck

What's important is selecting the right truck for the job. Some buyers go for lower GVWR trucks because they want to “save money.”

That usually doesn’t work out. There may be good reasons to buy Class 4 or Class 5 trucks – the fastest growing truck segment. In the correct application they can do a great job. But you need to understand the mission and expectations of the vehicle before buying the truck. Once you define the application, calculate what you want your vehicle to do and how it affects your choice of GVWR.

Here some questions: What’s your chassis weight? (Sometimes referred to as tare weight or GVW, which is the unladen weight of the vehicle.) What type of body? What’s the weight of the body? Will you also be towing a vehicle? What’s the weight of the vehicle or payload you’re towing? Your salesperson needs to make sure they understand your needs.

Weight Distribution

Here’s a weight distribution simulation using average weight from a Class 5, F-550 Ford regular cab with a 205-inch wheel- base. The cab and chassis tare weight is 7,800 lbs. and the truck has a 19,500-lb. GVWR. I added a 225-lb. driver, 200 lbs. of gear and a 19-foot, 6-inch steel carrier with an estimated weight of 5,900 lbs. Note that these are average estimates for demonstration. Your vehicle is likely to be different.

Our sample truck performed pretty well. If you place a standard car on the carrier – 3,500 lbs. or about the weight of a Ford Fusion – the truck is about 2,000 lbs. under the vehicle’s GVWR and, as important, about 2,000 lbs. under the rear axle capacity of 14,700 lbs. However, a 5,800-lb. Expedition means you’re at or slightly over maximum GVWR and rear axle capacity.

Weight distribution calculations are complex and depend on many variables including the truck wheelbase, center of gravity of the payload, weight of the payload and other factors. If the center of gravity of the payload is centered toward the rear of the truck, the bulk of the weight will transfer to the rear axle. Position a heavy object near the front of the bed and it may overload the front axle. Be mindful of the many variations and the effects they can have on your truck.

Towing Capacity

Towing capacity is referred to as the gross combined vehicle weight rating (GCVWR). There isn’t a common method by which all manufacturers calculate towing capacity. SAE is looking to establish a method, but today it’s up to the manufacturer.

Check with your vehicle’s manufacturer to determine your equipment’s towing capacity.

Towing a vehicle or load can push you into another GCVW class. Depending on the state, you can suddenly find yourself needing a CDL or a different license for the vehicle. Get caught and the fines can be painful.

In a Class 4 or 5 truck with a carrier bed, be careful towing a second vehicle on the wheel-lift with a load on the bed because the rear axle capacity can quickly be exceeded. The shift of weight to the rear can make steering control more difficult and upset the balance of the unit, and braking can also be difficult. Understand payload weights and how they affect the driveability of your truck.

Consequences of Overloading

Safety is the main reason not to overload. Over-loaded trucks can be difficult to control, difficult to stop and create a danger to the operator and potentially the public. Another reason not to overload is money – your money. Overloading can cause premature wear to numerous parts, costing money in repairs and downtime.

If you’re involved in an accident while overloaded, that’s a potential liability.

My suggestion – when looking for your next truck, carefully consider what you intend to do with the vehicle and consult a commercial truck salesperson to help you understand the equipment’s limits and guide you toward the chassis and body designed to meet your needs. Make the right choice and you’ll be happy for many years.

Dayton Shepard

is Executive Vice President at Lee-Smith, Inc. We offer commercial truck sales, parts service, motor coach repair, and we are the Southeast’s largest locally owned commercial truck dealer for International, Ford, and Isuzu Trucks.