CDL Practice Tests: Weight & Balance

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Question #628 (1 of 10)

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Adding or burning off fuel will mainly change the amount of weight on which axles?

  • Drive axles and somewhat on your trailer tandems
  • Trailer tandems only
  • Drive axles only
  • Steer axle and somewhat on your drive axles
Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles
Most of the weight of the fuel will go on your steer axle. The percentage of weight distributed between your steer and drive axles with regard to fuel will depend on the placement of your fuel tanks.
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Question #669 (2 of 10)

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Based on the following figures, how much fuel can you legally add while remaining legal on the drive axles?

Percentage of fuel weight to drive axles: 30%
Weight Before Fueling: Steer: 11,275, drives: 33,750, gross: 77,220

  • 88.5 gallons of fuel
  • 110 gallons of fuel
  • 104.13 gallons of fuel
  • 112.75 gallons of fuel
Once you know your current axle weights and the percentage of fuel weight that goes on the drive axles, you can use this formula to calculate the amount of fuel you can take on:

We know that 30% of the weight of fuel will go to the drive axles and you have 250 pounds you can add to the weight of the drive axles and remain legal. So plugging these numbers into the formula, you get:

250/30 = 8.33
8.33x100 = 833
833/8 = 104.13 gallons of fuel you can add
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Question #652 (3 of 10)

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What is the cargo's center of gravity?

  • The center point of the cargo's weight.
  • The average height of the cargo above the trailer floor.
  • The overall length of the cargo after being loaded into the trailer.
  • The distance from the front of the trailer to the center point of the cargo.
The center of gravity location of the cargo is the center point of the cargo's weight. In other words, if all of the cargo in your trailer was one solid block, the center of gravity would be the point that the entire block would balance upon like a teeter totter.
Sometimes you will load 22 pallets that all weigh the same. That makes it simple to determine the center of gravity. But often times you'll have a mixed product and you'll have to look over what's being put on the truck so you can get the weight of the cargo roughly centered between the drive axles and trailer tandems.
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Question #677 (4 of 10)

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Using the following numbers, what would be the final result if you moved the 5th wheel back one hole?

steer axle: 12,300 pounds
drive axles: 33,100 pounds
Weight transfer: 500 pounds per hole

  • steer axle: 12,050 pounds
    drive axles: 33,350 pounds
  • steer axle: 11,300 pounds
    drive axles: 34,100 pounds
  • steer axle: 11,800 pounds
    drive axles: 33,600 pounds
  • steer axle: 12,800 pounds
    drive axles: 32,600 pounds
If you move the 5th wheel toward the rear of the tractor, you will increase the weight on the drive axles and decrease the weight on the steer axle.
If you move it back 1 hole, then:

1 holes x 500 pounds per hole = 500 pounds of weight transfer from the steer axle to the drive axles.

12,300 - 500 = 11,800 pounds on the steer axle after transfer

33,100 + 500 = 33,600 pounds on the drive axles after transfer
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Question #626 (5 of 10)

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Sliding your trailer tandems forward or backward will redistribute the weight mainly between which two sets of axles?

  • None of these answers are correct
  • Steer axle and trailer tandems
  • Steer axle and drive axles
  • Drive axles and trailer tandems
Sliding your trailer tandems forward or backward will redistribute the weight mainly between your drive axles and trailer tandems
You may find a slight change in the weight of your steer axle after sliding your tandems, but it won't be very much and it's rarely much of a concern.
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Question #659 (6 of 10)

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What is the safe number to use in calculations for the weight of fuel?

  • 10 pounds per gallon
  • 8 pounds per gallon
  • 6 pounds per gallon
  • 7.25 pounds per gallon
The precise weight of diesel fuel will vary based on temperature and humidity, but is generally around 7.25-7.5 pounds per gallon. So the safest bet is to use 8 pounds per gallon as the number you'll plug into your calculations, and that's what we're going to use here.
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Question #649 (7 of 10)

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You receive a scale ticket and your drive axles are 35,400 and your trailer tandems are 31,100. Based upon the two most common tandem slider rail hole spacings, what is the minimum number of holes you would have to slide the tandems to get the weight legal, and in which direction?

  • 6 inch spacing - slide tandems back 5 holes
    4 inch spacing - slide tandems back 7 holes
  • 6 inch spacing - slide tandems forward 4 holes
    4 inch spacing - slide tandems forward 6 holes
  • 6 inch spacing - slide tandems back 4 holes
    4 inch spacing - slide tandems back 6 holes
  • 6 inch spacing - slide tandems forward 5 holes
    4 inch spacing - slide tandems forward 7 holes
The two main hole spacings you'll find are 4 inches and 6 inches. You can estimate that you will move 250 pounds per hole for 4 inch spacing, and 400 pounds per hole for 6 inch spacing.
With 35,400 pounds on the drive axles you must move a minimum of 1,400 pounds off the drive axles. To shift weight off the drive axles and onto the trailer tandems, you slide the trailer tandems forward toward the front of the truck.

With 6 inch spacing you're moving 400 pounds per hole so you need to move 4 holes to shift a minimum of 1,400 pounds (400 x 4 = 1,600).

With 4 inch spacing you're moving 250 pounds per hole so you need to move 6 holes to shift a minimum of 1,400 pounds (250 x 6 = 1,500).
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Question #660 (8 of 10)

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What is the best way to determine what percentage of the weight of fuel will go to each set of axles?

  • Ask another driver what their numbers are
  • Simply go by the number of gallons of fuel each tank holds
  • The percentage is standardized amongst manufacturers and is the same for every truck
  • Weigh the truck immediately before and after fueling, and do a simple calculation
The best way to determine what percentage of your fuel will go to each set of axles is to weigh the truck immediately before and after fueling, and do a simple calculation
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Question #651 (9 of 10)

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You receive a scale ticket and your drive axles are 35,700 and your trailer tandems are 30,600. Based upon a trailer with 4 inch slider rail hole spacings, what is the minimum number of holes you would have to slide the tandems to get the weight legal, and what would the final weights be?

  • Slide tandems forward 6 holes - 33,750 drive axles - 32,550 trailer tandems
  • Slide tandems back 7 holes - 33,750 drive axles - 32,550 trailer tandems
  • Slide tandems back 6 holes - 33,950 drive axles - 32,350 trailer tandems
  • Slide tandems forward 7 holes - 33,950 drive axles - 32,350 trailer tandems
The two main hole spacings you'll find are 4 inches and 6 inches. You can estimate that you will move 250 pounds per hole for 4 inch spacing, and 400 pounds per hole for 6 inch spacing.
With 35,700 pounds on the drive axles you must move a minimum of 1,700 pounds off the drive axles. To shift weight off the drive axles and onto the trailer tandems, you slide the trailer tandems forward toward the front of the truck.

With 4 inch spacing you're moving 250 pounds per hole so you need to move 7 holes to shift a minimum of 1,700 pounds (250 x 7 = 1,750).

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Question #678 (10 of 10)

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You're loaded heavy with 1/2 tank of fuel onboard. Using the following numbers, where should you move the 5th wheel to get it setup properly?

steer axle: 10,800 pounds
drive axles: 34,700 pounds
Weight transfer: 500 pounds per hole

  • Move the 5th wheel forward 2 holes
  • Move the 5th wheel forward 1 hole
  • Move the 5th wheel back 1 hole
  • Move the 5th wheel back 2 holes
The best way to make sure the 5th wheel is set properly is to scale the truck with a minimum of 1/2 tank of fuel and a very heavy load. Under those circumstances, you will want the 5th wheel positioned so that the steer tires are as close to 12,000 pounds as possible without going over, and the trailer tandems as close to 34,000 as possible without going over.
Moving the 5th wheel forward takes weight off the drive axles and puts it onto the steer axle. If we move it forward 2 holes and it transfers 500 pounds per hole, then we wind up moving 1000 pounds from the drive axles to the steer axle:

steer axle: 11,800 pounds
drive axles: 33,700 pounds
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About The Weight And Balance Section

This section was created by Trucking Truth to help people understand how to load cargo, scale the truck, and understand the laws about truck weight limits. These materials will not be on your written CDL exams but it is critical that every truck driver knows these materials.

Types Of Weight Limits

There are four basic weight limits: single axle, tandem axle, bridge formula, and gross vehicle. The Federal Standards are as follows:

  • 20,000 pounds single axle weight
  • 34,000 pounds tandem axle weight
  • 80,000 pounds gross vehicle weight
  • Bridge Formula Calculations

Why Do These Different Weight Limits Exist?

There are a long list of critical safety issues which require putting limitations on the gross weight, axle weights, the weight distribution across the length of a vehicle, and the weight distribution across a minimum number of axles.

  • Putting too much weight on a small area of the road surface can cause ruts, cracks, and potholes
  • Putting too much weight on a small area of a bridge surface can cause structural damage to the bridge
  • Too much weight on your steer axle can lead to a "heavy steering" feel and may cause the truck to react improperly to steering inputs
  • Not enough weight on your steer axle can lead to a loss of traction for your steer tires
  • Improper weight balance between your tractor drive tires and trailer tandems can lead to poor traction and an increased risk of jackknifing
  • Too much weight toward the back of the trailer can lead to a "pendulum effect", causing the rear of the trailer to sway back and forth while driving down the highway or jackknife going around a curve
  • Overloading a tire beyond it's maximum tire load capacity can cause tire damage and blowouts
  • Overloading the suspension system of the truck can cause damage to the suspension system which could easily lead to loss of control of the vehicle

So as you can see, it's critical in so many ways to make sure that we follow the weight limits in strict accordance with the law. It is incredibly dangerous to overload a vehicle or to have the weight improperly distributed across the axles.

Methods Of Weight Transfer

There are several ways to distribute the overall weight of the vehicle across the different sets of axles. You will affect weight distribution by:

  • Changing the weight distribution of the cargo along the length of the trailer, or moving the cargo around after loading the truth. This will distribute the weight mainly between your drive axles and trailer tandems
  • Sliding your trailer tandems forward or backward will redistribute the weight mainly between your drive axles and trailer tandems
  • Sliding your 5th wheel will redistribute the weight mainly between your steer axle and your drive axles
  • Adding or burning off fuel will mainly change the amount of weight on your steer axle and somewhat on your drive axles also, depending upon the placement of your fuel tanks.

Limitations On Weight Transfer

There are several factors that will reduce the amount of weight we can transfer between the different sets of axles on the truck:

  • Federal laws limit the maximum weight on any set of axles and the gross vehicle weight - 20,000 pounds single axle, 34,000 pound tandem axles, 80,000 pounds GVW
  • The bridge law formula limits the maximum amount of weight you can carry across any set of axles based upon the number of axles and the spacing between them (we'll discuss this formula soon).
  • The maximum legal length allowed between your trailer kingpin and your trailer tandems will limit how far back you can slide your tandems
  • The load rating of the tires you have will determine the maximum amount of weight allowed on any particular tire
  • The load rating of the suspension system will limit the amount of weight you can have on any axle

The Bridge Formula

bridge law formula and regulations for trucks

Congress enacted the Bridge Formula in 1975 to limit the weight-to-length ratio of a vehicle crossing a bridge. They accomplished this either by spreading weight over additional axles or by increasing the distance between axles.

The idea here was to prevent putting too much weight on a relatively small area, causing damage to the road surface and bridge structure. By requiring trucks to spread the weight across a longer distance and distributing the weight across more axles, you help prevent damage to the bridges and roadways.

Compliance with Bridge Formula weight limits is determined by using the following formula:

W = the overall gross weight on any group of two or more consecutive axles to the nearest 500 pounds.

L = the distance in feet between the outer axles of any group of two or more consecutive axles.

N = the number of axles in the group under consideration.

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.

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