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Scaling The Truck

Although the trucks we're referring to have five axles, when weighing the truck at a truck stop they will give you three sets of weights - the steer axle, the drive axles as a set, and the trailer tandems as a set. You are not weighing the drive axles or trailer tandem axles individually. They are scaled as a set and the weight limits you'll be shooting for are as shown in figure 3 to the left.

The legal weight limits for each set of axles is:

• Steer axle varies by state
• 34,000 for the drive axles
• 34,000 for the trailer tandems

The first image is a readout from an actual scale ticket at a truck stop (click to enlarge). As you can see, they'll list the steer axle, the drive axle(s), the trailer axle(s), and your gross weight.

The Steer Axle

There are various rules and regulations regarding the legal weight limit of your steer axle from state to state. Many states limit it to either 12,000 pounds or 20,000 pounds, but there are others that set a different limit or use a calculation based on tire tread width. For example, Kentucky has a limit of 700 pounds per inch of tread width. So if you have a 10-inch wide tire tread, you are allowed a maximum of 7,000 pounds per tire (700 pounds per inch x 10 inches wide) or 14,000 pounds total for the steer axle.

Keep in mind though - even if they allow 14,000 pounds on the steer axle, you have to have tires that are rated to carry that much weight. If your steer tires have a tire load limit of 6,000 pounds each, you can only carry 12,000 pounds on your steer axle, regardless of state laws.

You can look up the legal limits for each state in the Rand McNally Motor Carrier's Road Atlas.

Altering The Weight Distribution

The primary factors which will affect the weight distribution across a truck's axles are:

• The position of the trailer's tandems
• The position of the tractor's 5th wheel
• The overall weight of the cargo in the trailer and the horizontal (front-to-back) position of its center of gravity
• The amount of fuel onboard and the placement of the fuel tanks

In the coming pages, we'll go through these one at a time and learn to apply each one individually. Later we'll put them all together and show you how to get your truck's weight distribution legal out on the highways, coast to coast, under any circumstances.

Gross Weight Remains Unaffected By Weight Transfer

The final key point to understand for weight transfer is that none of the methods of redistributing weight between the different sets of axles, including sliding your 5th wheel, sliding your tandems, or moving the cargo around will have any effect on your gross weight. The gross weight will remain the same, while the amount of weight on each set of axles will change as you make these adjustments. This is an important point to keep in mind.

The only way to affect the gross vehicle weight would be to add or remove weight from the vehicle. Adding or burning off fuel, or adding or removing cargo would be two examples of ways to alter the gross vehicle weight.